Mohamed Ben Rashed

MBBCh, DCH, DTCH, Msc, PhD

Clinical Parasitology and Medical Entomology Department Medical Faculty / Alfatah University Tripoli/Libya

First Edition Preface

I am presenting this book , to become as a reference for medical students of third class, the teaching members of this field and the busy physician, I have prepared this synopsis in the hope that it will convey the correct , and modern information of medical entomology . I exert my best efforts to collect and to add of the best benefit from various modern books and references, most of it from the internet, to present this book in a complete Image. Iam sorry for any incompletion or non clear of any part, but certainly I will correct that in the coming edition. In intended more explaining in some of the diseases such as Plaque, Scabies, Myiasis and others, because these are the most important and dangerous diseases transmitted or caused by arthropoda which can leads to high rate of morbidity and mortality in the community . I wrote this to be an easy scientific reference to the student, that because I found many of them suffering and asking of non availability of any specific comprehensive reference covering their needs, also due to the expensive price of the references. And the contradictions of the teaching members on the priority of teaching, this happened in the different medical faculties in the Jamahirya.

Mohamed Ben Rashed Acknowledgments

Acknowledgments to Centers for Disease Control and Prevention , Division of Parasitic Diseases , for prevention to copy photographs.

I also acknowledge with gratitude the assistance received from : Dr- Nabile Jabr, head of parasitology department / Medical faculty/ Banha university; Egypt, for his effort to revise the book.

The Auther Contents

Preface

Acknowledgments

Introduction Phylum Arthropoda

Features of Arthropods

General arthropods morphology

The arthropoda and its ways can affect our health Class Insecta

Order: Diptera (true flies)

Biting flies

Mosquitoes

Simulium:Black fly

Chrysops:Horse fly

Stomoxys calcitrans:Stable fly

Glossina: tsetse fly

Phlebotomus/Lutozomiay:Sand fly

Culicoides: Midges

Non-biting flies

Filth flies

Musca vetstissima:Bush fly

Musca domestica: House fly Myiasis

Order: Dictyoptera

Cockroaches

Order: Coleoptera

Beetles

Order: Hymenoptera

Ants, Bees, Wasps

Order: Siphonptera

Fleas

Plaque

Sandflea

Order: Anoplura

Lice

Order: Hemiptera

Cimicidae:Bed bugs

Triatominae:Assassin bugs Class:Arachnides

Order: Acarina or Acari

Ticks

Mites

Scabies

Order : Araneida

Spiders Order Scorpionida

Scorpions Class Myriapoda

Order:Diplopoda:Millipedes

Order: Chilopoda:Centipedes

Class Crustacea:Cyclopes

Phylum Pentastoma:Linguatula serrata Terms and words meanings References Introduction

The discipline of medical entomology, or public health entomology, is focused upon insects and arthropods that impact human health. It include the insects of medical importance. An arthropod phylum is an invertebrate animal having an exoskeleton (external skeleton), a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda (from Greek arthron, "joint", and podos "foot", which together mean "jointed feet". Arthropods are characterized by their jointed limbs and cuticles, which are mainly made of α-chitin. The rigid cuticle inhibits growth, so arthropods replace it periodically by molting. The arthropods constitute an extremely diverse numbers of species .Most species are ectoparasites. Some species are directly responsible for morbidity and mortality of their hosts. Many arthropods serve additionally as intermediate hosts for helminth parasites, or vectors for serious protozoan, bacterial, or viral diseases.

Note: The phylum Arthropoda are divided into five classes. The class Insecta and Arachnida include most of the parasitic species or vectors of disease. The class Myriapoda have only the poisonous millipedes and centipedes, the Crustacea class contain few species that serve as intermediate host for animal parasites. The Onychophora class are not injurious.

Features of Arthropods • Exoskeleton - a hard protective covering around the outside of the body (divided by sutures into plates called sclerites) • Segmented body - that allows movement • Jointed limbs and jointed mouthparts - that allow extensive specialisation • Bilateral symmetry - whereby a central line can divide the body into two identical halves, left and right • Ventral nerve chord - as opposed to a vertebrate nerve chord which is dorsal • Dorsal blood vessel.

General arthropods morphology

Insects such as flies, wasps and cockroaches all have

• 3 body segments • 6 legs • 1 pair antennae

Arachnids include spiders, scorpions, ticks and mites. They all have

• 2 body segments - cephalothorax and abdomen • 8 legs • no antennae Head

The insect head is a sclerotised capsule of mainly rigid sclerites. It houses the compound eyes, simple eyes (ocelli), antennae and mouthparts.

Compound eye.

In most insects there is one pair of large, prominent compound eyes. It is composed of several units called ommatidia. There may be up to 30,000 ommatidia in a compound eye. This type of eye gives less resolution than the vertebrate eye, but it gives acute perception of movement -important in flight.

Digestive system

The digestive system is complete. The mouth is surrounded with jointed mouthparts that gather (possibly through piercing or biting) and manipulate food. The gut is usually divided into a foregut, midgut, and hindgut.

Circulatory system

The circulatory system is open; blood is pumped by a heart and circulates through the body cavity.

Nervous system

The nervous system is well developed, usually including eyes, antennae and other sensory structures.

Reproductive system

The male reproductive system consists of paired testes, each connected by vas deferens to a seminal vesicle, and then uniting to form an ejaculatory duct that enters a penis, which may have complex supporting structures associated with it. The female system consists of paired ovaries, each of which is connected by an oviduct to a vagina. A spermatheca is present. Accessory glands are present in both male and female systems.

Life cycles

Developmentally, arthropods proceed from an egg, through larval and/or nymphal stages, to the adult.

Note: Arthropods are usually ectoparasites, and may require 1 or more hosts to complete their life cycle. Many species move freely from one host to another, but others become attached permanently. Some species complete the entire life cycle on the host, but others attach only to feed and mate. Diversity

There are over 1,000,000 described species of arthropod; of course only a fraction are parasites. Probably the greatest morphological diversity occurs among the crustaceans. Some species look nearly identical to their free-living relatives except for some minor adaptations for attachment; others are barely recognizable as arthropods.

The arthropoda and its ways can affect our health

Nuisance flies, ants etc

Phobia

Spiders, cockroaches etc

Biting, sucking

Ants, bed bugs, Horse flies, mosquitoes, sand flies, fleas

Venoms and allergies

Wasps, ants, bees, spiders, ticks, dust mites

Disease, infestation

Head, body and pubic lice, mites (scabies), Myiasis

Disease vectors

Two vector methods:

• Mechanical - myxomatosis, bacteria by cockroaches and flies • Biological - requiring hosts in which the disease proliferates e.g. Malaria (disease) in humans (host) carried by mosquito (vector)

Class Insecta

Order Diptera (true flies)

The true flies are one of the most important and popular insect orders comprising more than 100,000 described living species. Minute to medium size, rarely large insects, usually with good flight abilities. Antennae variable, formed by two basal segments and multi-segmented (usually up to 20 flagellomeres) to one-segmented flagellum bearing sensory style or arista in the latter case. Mouthparts licking or biting . Pro- and metathoraces small, immovably fused with large mesothorax.

A- Bitting flies Mosquitoes

Mosquito (from the Spanish or Portuguese meaning little fly) is a common insect. Mosquitoes have mouthparts that are adapted for piercing the skin of plants and animals. There are about 3,500 species of mosquitoes found throughout the world. In some species of mosquito, the females feed on humans, and are therefore vectors for a number of infectious diseases affecting millions of people per year. While males typically feed on nectar and plant juices, do not bite and therefore they do not transmit disease. the female needs to obtain nutrients from a "blood meal" before she can produce eggs.

Note: The mosquitoes of medical importance are divided into: A-Anopheline mosquitoes which contains the important genus Anopheles. B- Culicine mosquitoes which contain three important genera, Aedes, Culex, and Man- sonia.

Morphology

Identifying Features of the morphology

• Eggs of some mosquitoes float on the water in rafts. • Larvae, often called wigglers, have a soft body, a hard head and a breathing tube, or siphon, at the tip of the abdomen. • Pupae are shaped like a comma, and are commonly called tumblers. • Adults have delicate legs, a long proboscis and one pair of transparent wings.

The mosquitoes have two wings, but unlike other flies, their wings have scales. The mouthparts of female mosquitoes form a long piercing-sucking proboscis which can pierce skin and suck blood. Males differ from females by having feathery antennae and mouthparts not suitable for piercing skin. Female mosquitoes are usually larger than males. Females have fine thread like antennae with few hairs, whereas males have bushy antennae.

Adult - Length of the adult varies but is rarely greater than 16 mm (0.6 in) and weight up to 2.5 mg (0.04 grain). All mosquitoes have slender bodies with three sections: head, thorax and abdomen. Mosquitoes are long-legged insects with one pair of wings 3 to 4 mm long. The wings, legs, back (thorax), and abdomen are variously colored. Mosquitoes can be distinguished from all other two-winged insects by the long beak (proboscis), which is used in feeding, and the scales on their wings. Male mosquitoes have bushy antennae and do not bite.

The male on the left, females on the right. Note the bushy antennae .

Anopheles wing pattern showing pattern Aedes, showing distinctive white scales.

Egg - The small, white cylindrical eggs taper at one or both ends and darken with age.

Adult anophelus females lay 50-200 eggs per oviposition. The eggs are quite small (~0.5 x 0.2 mm).

Larva - Young larvae are difficult to see because they are light colored or nearly transparent and only about 3 mm long. Mature larvae, on the other hand, are usually greenish-brown or brown and up to 10 mm long. The head is distinct and usually dark on all four instars. Upon close inspection, most of these elongate larvae are quite hairy. Larvae breathe through spiracles located on the eighth abdominal segment, or through a siphon, and therefore must come to the surface frequently. The larvae spend most of their time feeding on algae, bacteria.

Pupa - Smaller than mature larvae, pupae are comma-shaped with a slender, curved abdomen. They move through the water in a tumbling motion; hence, they are commonly called "tumblers." The head and thorax ar e merged into a cephalothorax with the abdomen circling around underneath. As with the larvae, pupae must come to the surface frequently to breathe,

The main differences between Anopheline and Culicine mosquitoes are

Adult: Anopheles mosquitoes can be distinguished from other mosquitoes by the palps, which are as long as the proboscis, and by the presence of discrete blocks of black and white scales on the wings. Adult Anopheles can also be identified by their typical resting position: males and females rest with their abdomens sticking up in the air rather than parallel to the surface on which they are resting.

Eggs: Eggs of Anopheles and Aedes mosquitoes are laid singly, while those of Culex mosquitoes are deposited in raft-like masses.

Larvae: Anophelus mosquito larvae have a well-developed head with mouth brushes used for feeding, a large thorax and a nine segmented abdomen. They don't have legs. In contrast to other mosquitoes, Anopheles larvae lack a respiratory siphon and for this reason position themselves so that their body is parallel to the surface of the water. Aedes, Anopheles and Culex larvae. An indication of the genera of mosquito larvae can be made from the length of the siphon. Anopheles have very short siphons (see below also), while Culex tend to have the longest siphons.

Aedes, Culex larvae and pupa. Both Aedes and Culex larvae hang down from the water surface at an angle.

Life cycle

Mosquitoes go through four stages in their life-cycle: egg, larva, pupa, and adult or imago. Adult females lay their eggs in standing water, which can be a salt-marsh, a lake, a puddle, a natural reservoir on a plant, or an artificial water container such as a plastic bucket. For most species of mosquito, the life cycle from egg through the larval stage to the adult takes about 10-14 days. For Mansonia species the life cycle takes up to 3 weeks. The lifespan of an adult mosquito is generally 3-4 weeks, although it may be reduced in nature due to natural enemies.

Note- Any water surfaces such as in the small pond, marsh or swampy area and even water buckets are the breeding ground of mosquitoes.

Medical importance

A-Viruses diseases transmitted by mosquitoes

Arthropod-borne viruses (arboviruses) are viruses that are maintained in nature through biological transmission between susceptible vertebrate hosts by blood feeding arthropods (mosquitoes and ticks). The majority of human infections are asymptomatic or may result in a nonspecific flu-like syndrome. Onset may be insidious or sudden with fever, headache, myalgias, malaise and occasionally prostration. Infection may, however, lead to encephalitis, with a fatal outcome or permanent neurologic sequelae. Fortunately, only a small proportion of infected persons progress to frank encephalitis.

Chikungunya The disease occurs through Africa, India and Southeast Asia, generally from May to July. (Aedes spp).

Dengue Occurs in most tropical regions including Southeast Asia, Australia, Central America, North America, South America, India and Africa. (Aedes spp).

Eastern Equine Encephalitis Infections occur mainly between May and August, mostly in the US and also Canada.(Aedes and Mansonia).

Japanese Encephalitis Known from southeast Asia, China, Japan, India, Korea and was recently introduced into the Torres Strait Islands of far north Australia. (Culex spp).

St Louis Encephalitis;The disease mainly occurs in the US, peaking through the months from June to October.(Culex spp).

Venezuelan Equine Encephalitis; Occurs in southern and Central America. (Culex spp).

Western Equine Encephalitis Occurs in the western areas of North America and also in South America, generally midsummer. (Culex spp).

Yellow fever; The disease occurs in tropical regions of Africa, and central /south America, peak incidence during rainy seasons. (Aedes spp)

Mayaro virus; The disease has been recorded from South America and the West Indies and the virus has been recorded infecting humans in Central America. Epidemics occur during and around the rainy season. (Culex spp)

Murray Valley Encephalitis and Kunjin; Known from Australia and New Guinea and generally occurs through the first four months of the year. (Culex spp)

O'Nyong-nyong virus; Only known from Africa and tends to be more common when the vectors are in large numbers following seasonal rains. (Anophelus spp)

Oropouche Fever; Occurs through the rainy seasons of January to June mainly in Brazil. (Culex spp)

Rift Valley Fever; Outbreaks tend to follow heavy rains. Only occurs in Africa. (Aedes spp)

Rocio Encephalitis Epidemics peak from March to May. The disease occurs in southern Brazil. (Culex and Aedes spp) Ross River and Barmah Forest virus; both produce a disease traditionally known as "Epidemic Polyarthritis". The disease occurs in Australia and mostly peaks in the first three months of the year. Outbreaks have occurred in the western Pacific Islands. (Aedes and Culex spp)

Sindbis and Ockelbo virus; Very widespread and occurs in most continents, although disease from Sindbis is rare in Australia. (Aedes spp)

West Nile Fever;. Activity is mostly confined to the summer months and occurs in Africa, Europe, the Middle East and the former USSR.(Culex and Aedes spp)

La Crosse encephalitis Most cases of LACV disease occur in the upper Midwestern and mid-Atlantic and southeastern states. (Aedes spp)

B- Parasitic diseases

Malaria; this disease results from infection with a protozoan blood parasite transmitted by various species of mosquitoes belonging to the genus Anopheles.

Lymphatic Filariasis; caused by nematode worms which block lymphatic vessels and produce the condition known as "Elephantiasis" (a gross swelling, usually in the legs and scrotum). transmitted by various species of mosquitoes belonging to the genus Culex,Aedes, Mansonia.and Anophelus transmit Malayan filariasis.

Black fly

A black fly (sometimes called a buffalo gnat, turkey gnat, or white socks) is any member of the family Simuliidae. It is small blackish stout-bodied biting fly having aquatic larvae; sucks the blood of birds as well as humans and other mammals. They spread several diseases. Simulium flies are found in forest or savannah regions along .the courses of free flowing well-oxygenated rivers and streams

Morphology

Adult black flies (Simulium spp.) are small , measuring 1.5-4 mm in length with a humpbacked appearance. They have short horn like antennae and short legs . They are mostly black and white (a few species are yellow or less commonly orange). The head bears large compound eyes and short mouth-parts. In the female the mouth-parts are adapted for tearing and piercing the skin.

Adult Larvae (top) - Puba (bottom)

Life cycle The eggs are laid on rocks just below the surface of flowing water or on vegetation dipping into the water. The larvae and pupae remain attached to rocks and dead leaves, feeding on small organic particles filtered from the water. There are six to nine larval stages. Breeding is greatly increased in the rainy season.

Medical importance

The black fly is central to the transmission of the parasitic nematode Onchocerca volvulus, which causes Onchocerciasis, also known as river blindness. Black fly attacks on people, cattle, horses and pigs tend to be concentrated around the ears and head. In addition to the blood loss, effects of the insect saliva can cause a variety of problems, with swelling and intense skin irritation most common. Allergenic asthma, nausea and more systemic effects can also occur, a condition known as "black fly . ".fever

Note: Adult black flies are migratory, commonly flying many miles from larval breeding sites. As an extreme example, migrations of more than 90 miles are reported in Canada , this an important cause of control failure .

Chrysops flies (Horseflies)

Family Tabanidae, are commonly called horse flies or deer flies. they are among the world's largest true flies. They are known to be extremely noisy during flight. Flies of this type are among those known sometimes as gadflies, zimbs or clegs. In Australia, they are known as "March Flies". In some areas of Canada, they are also known as Bull Dog Flies. Worldwide distribution. live in the African equatorial rain forest. Attracted by smoke or human activity in forest .The female feeds on blood and plant juices and the male on plant juices only.

Morphology Chrysops flies are medium to large (6-30 mm)Antennae are small but stout,Mouthparts adapted for biting,hang downwards from head , triangular head , broad wings.The abdomen is yellow or orange and often patterned with black stripes or other markings. The abdomen, thorax, and legs are covered with small hairs.

Life cycle Eggs are laid on plants . The larvae hatch and drop into the mud where they live for several months, feeding on small organisms. After growing and moult- ing they pupate on drier ground. Development takes several months.

Medical importance

Tabanids known vectors for some Blood-borne diseases of animals and humans. Tabanids are very good vectors of the Equine Infectious Anaemia Virus, as well as some Trypanosome species. Species in the genus Chrysops are biological vectors of Loa loa, transmitting this parasitic filarial worm between humans.The western deer fly C.discalis has transmitted tularemia to both man and animals. Also act as mechanical carriers of bacteria and some protozoa. They have also been known to transmit Anthrax among cattle and sheep. Blood loss is a common problem in some animals, when large flies are abundant. Some animals have been known to lose up to .300 ml of blood in a single day, which can severely weaken or even kill them

Stable fly

Stomoxys calcitrans is commonly called the stable fly, barn fly, biting house fly, dog fly, or power mower fly. It is an annoying pest of man and animals. It is small oval, grayish fly resembles but it is larger slightly than the house fly, distinguished by its bayonet –shaped proboscis, robust appearance, dark color, thorax with four dark longitudinal stripes. The habit stable flies have of leaving one animal to feed on another makes them ideal mechanical vectors of disease . S.calcitrans is the mechanical vector of Trypanosoma evansi (surra) in cattle and horses

Adult Stable fly

Glossina (Tsetse) Flies About 23 species belong to this family of the diptera.divided into two main groups: Savannah group (Morsitans) which are associated with rhodesiense trypanosomiasis. Riverine group (Palpalis)which are mainly the vector of gambiense trypanosomiasis. Both the male and female tsetse flies suck blood. They feed from humans, other mammals, and reptiles. Species of the palpalis group of flies live in vegetation bordering rivers, lakes, and other water places, whereas tsetse flies of the morsitans group prefer arid wooded savannah areas away from water.

Morphology Tsetse flies are large yellow-brown or brown-black flies, measuring 6-15 mm in length., widely spaced eyes, forward-projected mouth parts and the wings show a characteristic axe- shaped venation . The thorax shows markings and in some species the abdomen is striped and spotted.

Life cycle A tsetse fly does not lay eggs but produces a single fully developed larva, which on leaving the female, pupates in an area of shaded vegetation just below the surface of the soil. Then the adult emerges .

Medical importance Tsetse flies transmit human african and animal trypanosomiasis (sleeping sickness).

Sandflies

Sandfly is a colloquial name for any species or genus of flying, biting, blood-sucking Dipteran encountered in sandy areas. Are minute biting insects .They fly near to the ground in short hop-like flights . Sand flies survive by sucking blood from humans and animals. Females need blood to survive, whereas males do not need it and cannot bite. Phlebotomus species are found in warm and hot climates, in dry desert-like regions .Lutozmyia species in humid forest areas.

Morphology Sandflies are small, hairy, yellow or grey-coloured insects, measuiing 3-5 mm in length with long antennae, long weak legs and upward erected wings .

Life cycle After blood meal, female lay 30-50 elongated eggs in dark moist crevices. After 6-12 days the eggs develops into segmented caterpillar like larva with long caudal bristles, the larva molts four times befor become a buff coloured pupa . The adult emerge from the pupa in 6-14 days.

Medical importance

Phlebotomus sandflies are vectors (in old world) of:

• Visceral leishmaniasis • Cutaneous leishmaniasis • Sandfly fever • Oroya fever (Carrion’s disease)

Lutozomyia are vectors (in new world) of:

• Visceral leishmaniasis • Cutaneous leishmaniasis

• Mucocutaneous leishmaniasis

• Sandfly fever • Oroya fever (Carrion’s disease)

Midges (Culicoides )

Culicoides is a genus of biting midges. midges are minute insects, often called "no- see-ums" because they are so small that they can pass through typical porch screening. However, despite their size, they can be painful biters and highly annoying. Culicoides species live in swampy areas along the banks of rivers and pools, in mud .and sand soaked by sea water.The female sucks blood. The male feeds on plant juices

Morphology Culicoides flies are small, measuring less than 2 mm in length. They are dark coloured with a humped thorax and small spotted wings. The antennae are long and . the mouth-parts of the female are adapted for sucking blood

Biting midges

Life cycle Two to 3 days after a blood meal, females will lay their eggs in well lit, damp areas on plants in the water or on mud containing large amounts of decaying organic material, which favor larval development. The eggs will hatch 48 to 72 hours later, the larvae will go through four larval instars. Within 10 to 14 days the larval instars are complete and the larvae will become pupae; within 2 to 3 days adults will emerge from the pupae.

Medical importance

Culicoides flies, also known as biting midges, transmit a wide range of both human and veterinary diseases. less pathogenic filarial worms Mansonella perstans, Mansonella streptocerca, and Mansonella ozzardi Also it transmit Oropoche virus , Blue tongue virus and African horse sickness viruses.

B-Non-Biting Flies

Filth flies

These flies are responsible for contamination and spoilage of foodstuffs, annoyance, mechanical transmission of disease-causing pathogens, and invasion of living tissues (myiasis). Collectively known as "filth flies", they are distributed throughout the families of Calliphoridae (blow flies), Sarcophagidae (flesh flies) and Muscidae (house flies). Flies can be strongly attracted to uncovered, malodorous wounds, body openings, open sores or damaged skin. Some species will deposit their eggs or larvae on the site if the circumstances are suitable. This can result in myiasis, wherein young maggots feed on healthy or diseased tissue to complete their growth cycle.

Bush fly", Musca vetustissima. This fly is a major pest which breeds in manure in pastures and disperses widely to surrounding rural and adjoining urban environments throughout the summer months. These flies are annoying, constant companions of humans and livestock which they visit in large numbers, and attempt to feed at the mouth, nose, eyes or wounds at every possible moment. Bushflies have been known to transmit eye infections and other enteric diseases by their continual interchange between other animals and humans.

Houseflies (Musca domestica) One of the commonest houseflies is Musca domestica which belongs to the family Muscidae.

Morphology

M. domestica is about 8 mm in length, grayish black with four dark stripes on its thorax and a variable amount of orange marking on its abdomen .The antennae are short and the proboscis is retractable. Life cycle M. domestica lays its eggs in masses in manure and other decaying refuse. In warm conditions larvae (maggots) hatch within 24 hours and pupate after about 5 days. Adults emerge after about 3 days and live for about 1 month.

Medical importance

Diseases which M. domestica can transmit mechanically include:

• typhoid • bacillary dysentery • cholera• brucellosis • tetanus • streptococcal infections • amoebic dysentery • poliomyelitis, hepatitis, and other viral disease plus various parasites such as pinworm and tapeworm; however, in modern developed societies with high standards of hygiene, fly-borne disease is relatively uncommon.

Note:Although M. domestica is a non-blood sucking, it is important medically because it can ingest and transfer parasitic eggs and cysts, bacteria, and viruses from infected faeces to human food. Pathogenic organisms are easily transmitted because the feeding habits of the fly involve regurgitation of its crop contents and defaecation while feeding.

Myiasis

Myiasis(In Greek, "myia" means fly) is the infestation of tissue with parasitic dipterous fly larvae, feeding on the host's necrotic or living tissue. Larvae commonly referred to as maggots. It is widespread in the tropics and subtropics of Africa and the Americas, and occurs with significantly less frequency in most other areas of the world. Myiasis can come in all sorts of variations, depending on the fly species and where the larvae are located. Some flies may lay eggs in open wounds, other larvae may invade unbroken skin or enter the body through the nose or ears, and still others may be swallowed if the eggs are deposited on the lips or on food. Myiasis may be caused in human hosts by several species of arthropods of the order Diptera, the two- winged true fly.

Vectors in humans

There are three main fly families causing economically important myiasis in livestock and also, occasionally, in humans:

• Calliphoridae (blowflies) • Oestroidea (botflies) • Sarcophagidae (fleshflies)

Other families occasionally involved are:

• Anisopodidae • Piophilidae • Stratiomyidae • Syrphidae

Dermatobia hominis (Bot fly) Frontal /lateral view.

Classification of Myiasis

Myiasis can be classified in two ways:

A-The classical classification describes the myiasis by the infected area of the host. Dermal, sub-dermal, cutaneous , nasopharyngeal , ocular , intestinal/enteric , or urogenital .

B-Another classification is based on the relationship between the host and the parasite . Thus the myiasis is described as either specific, semispecific, or accidental. This describes whether the fly larvae require a host for development as the following.

1- Obligatory (Specific) Agents Both D. hominis and C. anthropophaga are obligatory parasites, whose larval stages can occur only in the living tissue of animal or human hosts. Myiases caused by larvae of the human botfly and the tumbu fly predominate, but several other species that generally parasitize animals occasionally cause infections in humans as well. Other obligatory flies include the genera Oestrus, Rhinoestrus, Gasterophilus, Hypoderma, Chrysomyia, and Wohlfahrtia. Transmission and the type of tissue affected varies with the species of the parasite.

2- Facultative (Semi-specific) Agents Flies of the family Sarcophagidae normally develop in decomposing tissue and are considered facultative parasites. Larvae of these flies parasitize wounds and other damaged tissues, and some species further invade living tissues adjacent to the wound. Important genera in this category include Musca, Calliphora, and Lucilia.

3- Accidental (Non-specific) Agents Accidental myiasis occurs when egg-stage flies are ingested on contaminated food or come in contact with the genitourinary tract. Flies of the families Muscidae, Calliphoridae, and Arcophagidae may be involved (Powers and Yorgensen).

Adult of Cochliomyia hominovorax, the primary screw worm fly in the New World.

Cochliomyia hominovorax is the primary screwworm fly in the New World. Larvae are obligate parasites of living flesh in humans and other mammals. Human cases are not common but may be seen in regions where livestock is tended. Female flies oviposit on or near pre-existing wounds or on mucous membranes just inside the nose or mouth. Larvae feed subdermally and may cause extensive tissue damage. Human deaths have occurred from tissue destruction. Human cases have been drastically reduced in the United States and Mexico by a sterile male release program. Females mate only once, so mating with a sterile male ensures the next generation will not happen.

Clinical Presentation in Humans

How myiasis affects the human body depends on where the larvae are located. Larvae may infect necrotic (dead) or living tissue in various sites: the skin, eyes, ears, stomach and intestinal tract, or in genitourinary sites. They may invade open wounds and lesions or unbroken skin. Some enter the body through the nose or ears. Larvae or eggs can reach the stomach or intestines if they are swallowed with food and cause gastric or intestinal myiasis.

Several different presentations of myiasis and their symptoms:

Syndrome Symptoms Painful, slow-developing ulcers or furuncle- (boil-) like sores that Cutaneous Myiasis .can last for a prolonged period Obstruction of nasal passages and severe irritation. In some cases Nasal Myiasis .facial edema and fever can develop. Death is not uncommon Crawling sensations and buzzing noises. Smelly discharge is Aural Myiasis sometimes present. If located in the middle ear, larvae may get to .the brain Ophthalmomyiasis .Fairly common, this causes severe irritation, edema, and pain

Furuncular breast lesion with multiple sinuses containing Tumbu fly larvae.

Diagnosis

Myiasis is often misdiagnosed in the United States because it is extremely rare and its symptoms are not specific. Intestinal myiasis and urinary myiasis are especially difficult to diagnose. Clues that myiasis may be present include recent travel to an endemic area, one or more non-healing lesions on the skin, itchiness, movement under the skin or pain, discharge from a central punctum (tiny hole), or a small, white structure protruding from the lesion.

Treatment

First the larvae must be eliminated through pressure around the lesion and the use of forceps. Secondly the wound must be cleaned and disinfected. Further control is necessary to avoid further reinfestation.

Larvae removal by foreceps

Note: Recent research overseas has revived the interest in the "benefits" of some maggots and some medical units are now using "clean" maggots to aid in the cleansing of decaying flesh of humans.

Prevention The prevention of myiasis is mainly by reducing the numbers of flies, by sanitary measures, and the use of insecticides. It may also be necesary to use repellants, screening, and protective clothing.

Order Dictyoptera

Cockroaches

There are nearly 4000 species of cockroach, distributed throughout most parts of the world. Living mainly in humid places, including human dwellings, caves and ants' nests,Scavenge most organic matter.Family Blattidae are important household pests and may be mechanical vectors of pathogenic organism as well as intermediate hosts of helminthic parasites.

Morphology Cockroaches vary greatly in size from 5 mm to 9 cm in length. They have three pairs of legs and most species have two pairs of wings . The body is divided into: A clearly defined head which bears a pair of long antennae. A thorax which has a large pronotal area. A large elongated abdomen.

Life cycle Cockroaches after mating the female lays an egg-case which contains 12 to 48 eggs according to species. The eggs hatch nymphal insects which look like adults except they are much smaller and have no wings. The nymphs become adults by passing through as many as twelve moults and therefore may take as long as 18 months to reach maturity.

Medical importance There is increasing evidence that cockroaches may act as mechanical carriers and efficient reservoirs of pathogenic organisms. Domestic cockroaches have been shown to harbour a wide variety of pathogens in their hindgut and on their body surface, including: • major pathogenic enterobacteria • polioviruses • hepatitis viruses • Entamoeba histolytica • several nematodes.2 Cockroaches can transmit pathogens by walking over and defaecating on food or by transmitting pathoges in vomit drops or from their legs and body surfaces.

Order Coleoptera

Beetles

Many species are medically important such as Lytta vesicatoria (Spanish fly) contain blister fluid, from this beetle a substance obtained by beetles grounding known as cantharidin , this substance cause irritation with erythema and vesicle formation formation when come in contact with the skin.. this powder (cantharidin) used as a rubefacient, diuretic and aphrodisiac. Flour Beetle larva and adult serve as intermediate host of some helminthic disease such Hymenolepiasis.

Order Hymenoptera

Ants, Bees, Wasps

The most familiar Hymenoptera are the bees, wasps and ants; insects feared by many people because of their stings. However, these make up only a small proportion of the order.

Ant Bee Wasp

Hymenoptera is one of the largest orders of insects, comprising the wasps, bees, and ants. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek (hymen): membrane and (pteron): wing. The hindwings are connected to the forewings by a series of hooks called hamuli.

Bee, Wasp Stings Hymenoptera stings will only cause local pain and swelling. However, some individuals may be allergic to Bees and wasps stings cause, An allergic reaction to Hymenoptera stings occurs once the victim becomes sensitized to the venom from a previous sting. The allergic reaction is caused by the immune system, which has now been oversensitized to the venom and releases histamines into the bloodstream. Histamines dilate blood capillaries, causing the skin to appear red and feel warm, and also make the capillaries more permeable, which allows fluid to escape into the tissues. This causes swelling, which is manifested as rapidly appearing hives, accompanied by severe itching. In a severe allergic reaction called anaphylactic shock, the tissues of the throat swell and the victim may have difficulty breathing and, unless promptly treated, death may result.

Note: Bee stings cause about 17 deaths per year in the USA.

Symptoms of wasps and bees stings pain, redness, swelling, and itching. produce immediate pain and a red, swollen, sometimes itchy area about (1 cm) across. In some people, the area swells to a diameter of 5 cm or more over the next 2 or 3 days. This swelling is sometimes mistaken for infection, which is unusual after bee stings. Allergic reactions may cause rash, itching all over, wheezing, trouble breathing, and shock. Allergic reactions are uncommon but may be serious.

Treatment A bee may leave its stinger in the skin. The stinger should be removed as quickly as possible by scraping with a thin dull edge (for example, the edge of a credit card or a thin table knife). An ice cube placed over the sting reduces the pain. A cream or ointment containing an antihistamine, an anesthetic, a corticosteroid, or a combination of them is often useful. Severe allergic reactions are treated in the hospital with epinephrine, intravenous fluids, and other drugs. People who have had a severe allergic reaction to a bee sting sometimes undergo desensitization (allergen immunotherapy —see Allergic Reactions

Ant sting

The stinging ants cause little injury, but the small fire ant of the genus Solenopis, which is found in southern united states, cause a fiery sting and pruritic vesicles.The fire ant sting usually produces immediate pain and a red, swollen area, which disappears within 45 minutes. A blister then forms, rupturing in 2 to 3 days, and the area often becomes infected. In some cases, a red, swollen, itchy patch develops instead of a blister. Isolated nerves may become inflamed, and seizures may occur.

Vesicles caused by (Fire Ant Sting)

Order: Siphonptera/ siphon = tube; aptera = wingless

Flea

Small insects generally living as ectoparasites of mammals and birds. Fleas transmit various pathogens, including tapeworm and bubonic plague. Both males and females feed exclusively on blood and may live up to 12 months.

Morphology

Fleas are small (1 to 6 mm) long , agile, usually dark colored (for example, the reddish-brown of the cat flea), wingless insects with tube-like mouth-parts adapted to feeding on the blood of their hosts. Their legs are long, the hind pair well adapted for jumping: a flea can jump vertically up to 7 inches (18 cm) and horizontally up to 13 inches (33 cm). and easily recognized because they are greatly flattened laterally. The body is covered with backward pointing spines which give easy forward movement in the fur of animals. The thorax, as in all insects, is divided into 3 segments, and the abdomen has 10- 12 segments. The presence or absence of genal and pronotal combs is used in the identification of fleas. The larvae are elongated and worm-like, Mature larvae are 4–10 mm long.

Life cycle Fleas are holometabolous insects, going through the four life cycle stages of egg, larva, pupa, and imago (adult). The larva , which hatches from a 0.3–0.5-mm-sized egg , has no eyes and reaches a length of 4–10 mm when fully grown. There are usually three larval instars, but only two in Tunga penetrans. Larvae feed on organic debris and on undigested blood from the feces of adults. The differentiated third-stage larva constructs a loosely woven cocoon (3 × 1 mm) which may become encrusted by sand . Inside, the flea pupates , and remains quiescent until it emerges as an adult (females emerge 3–4 days before the males).

Medical importance

Flea bites

Flea bites are most common on areas of the body with tight clothing, especially the lower legs & around the waist. The itching of flea bites is caused by an allergic reaction. Sensitivity to flea bites varies between people; children often have especially severe reactions. In sensitive people, the bite is often surrounded by a "halo" of red, irritated skin..

Flea bites

Besides the problems posed by the creature itself, fleas can also act as a vector for disease. Fleas transmit not only a variety of viral, bacterial and rickettsial diseases to humans and other animals, but also protozoans and helminths.

• bacteria: Murine or endemic typhus. Fleas have helped cause epidemics by transmitting diseases such as the bubonic plague between rodents and humans by carrying Yersinia pestis bacteria. Fleas can transmit Yersinia pestis, Rickettsia typhi, Rickettsia felis, and Bartonella henselae. • virus: myxomatosis. • helminth: infestation of Hymenolepiasis tapeworm. • protozoa: Trypanosome protozoans such as those of the subgenus Herpetosoma, use a variety of flea species opportunistically as vectors.

Main fleas of medical importance are especially the tropical rat flea Xenopsylla cheopis, the sand flea Tunga penetrans, the cosmopolitan human flea Pulex irritans – all possessing no combs – and the cat flea Ctenocephalides felis. The incidence of the major transmitted disease, plague, has decreased markedly during the last 80 years. Since the rodent hosts cannot be eradicated, outbreaks of plague will regularly occur in many parts of the world, e.g. India and Russia, Pulex species

Pulex irritans is known as the human flea. Adults are 1-4 mm in length and laterally-compressed. They lack both genal and pronotal combs and the ocular setae are below the eye. This species is not an efficient vector of any flea-borne diseases, but its bite can cause allergic reactions due to salivary proteins. p. irritans is the human flea and has a worldwide distribution. By its frequent and prolonged feeding on the blood of its host, it causes discomfort and irritation.

Ctenocephalides species (fleas of cats and dogs) The cat flea is the most common ectoparasite of both dogs and cats in the United States and has been found on over a dozen other animals, have both genal and pronotal combs (ctenidia), differentiating them from most other fleas of domestic animals. .These fleas are medically important because they serve as hosts for the tapeworms D. caninum, H. diminuta, and H. nana . When ingested by flea larvae, the eggs develop into the infective cysticercoid larval forms. Humans become infected by accidently swallowing a flea which contains these cysticercoid larvae. The cat fleas, Ctenocephalides felis felis and C. f. orientis can also cause intense allergic reactions in humans.

Cat flea: eggs Larva Adult

Adult cat flea

Tunga species T. penetrans, also known as the jigger flea, or chigoe, and bicho do pé or sand flea can be found in South America, Africa, and India. The head is angular, it has no comb of spines, and the thoracic segments are narrow at the top.The female feeds by burrowing into the skin of its host. The abdomen becomes enormously enlarged between the second and third segments so that the flea forms a round sac with the shape and size of a pea. It is the female jigger flea which is medically important because it requires an endoparasitic existence for egg development. The pregnant female burrows into the skin of its host, often around the toes, fingers, or other parts of the body. The greatly enlarged flea. Produces an irritating and often painful swelling just under the skin. Over a period of several days the eggs are discharged through the skin, after which the female dies. Irritation causes tissue damage which may lead to secondary bacterial infection. Control of tungiasis is difficult. In endemic areas, preventive measures include the wearing of shoes and the use of insecticides.

The impregnated female Tunga embeds itself in the skin under the toe nails and finger nails where the resultant sores may fill with pus and become infected .

Xenopsylla species

Xenopsylla cheopis is known as the Oriental rat flea and is the primary vector for Yersinia pestis (plague). Adults are 1.5-4 mm long and laterally-compressed. They lack both pronotal and genal combs (ctenidia).

Note: In the genus Xenopsylla, the rat fleas X. cheopis, X. astia, and X. brasiliensis are medically important species because they are carriers of: • Bubonic plague • Flea-borne murine typhus (endemic typhus) X. brasiliensis occurs in Africa, South America, and India, infesting rats mostly in villages and also in ports. X. astia is found in South East Asia and Indonesia. It naturally infests rats in fields, villages, and ports. Other rat fleas which can carry plague and can live on humans include X. vexabilis, found in the Pacific Islands and infesting rats mainly in fields, and the rat flea Nosopsyllus fasciatus which has a worldwide distribution and is found mainly in the ports of cool temperate countries.

Plague

If the fleas suck blood of a plague-infected host, the causative agent Yersinia pestis is transmitted and multiplies in the lumen of the gut, especially in the foregut, initially resulting in a plug of bacteria which later is partly reduced. The blockage is stronger in the more virulent strains of bacteria which adhere stronger to each other. From the foregut or contaminated mouth parts the bacterium is transmitted to the vertebrate host. Yersinia pestis is pathogenic to fleas due to the blockage of the proventriculus by a plug. Since only reduced volumes of blood can be ingested, infected fleas attack hosts more often. Plague is an infectious disease that affects animals and humans. It is caused by the bacterium Yersinia pestis. This bacterium is found in rodents and their fleas and occurs in many areas of the world, including the United States.

Bubonic plague is the most common form of plague. This occurs when an infected flea bites a person or when materials contaminated with Y. pestis enter through a break in a person's skin. Patients develop swollen, tender lymph glands (called buboes) and fever, headache, chills, and weakness. Bubonic plague does not spread from person to person.

Note: Bubonic plague was a major factor stopping Napoleon's invasion of Palestine and Syria in 1799.

Pneumonic plague occurs when Y. pestis infects the lungs ,it may occur separately or in combination. This type of plague can spread from person to person through the air.Transmission can take place if someone breathes in aerosolized bacteria, which could happen in a bioterrorist attack. Pneumonic plague is also spread by breathing in Y. pestis suspended in respiratory droplets from a person (or animal) with pneumonic plague. Becoming infected in this way usually requires direct and close contact with the ill person or animal. Pneumonic plague may also occur if a person with bubonic or septicemic plague is untreated and the bacteria spread to the lungs. The first signs of illness are fever, headache, weakness, and rapidly developing pneumonia with shortness of breath, chest pain, cough, and sometimes bloody or watery sputum. The pneumonia progresses for 2 to 4 days and may cause respiratory failure and shock. Without early treatment, patients may die.

Septicemic plague occurs when plague bacteria multiply in the blood. It can be a complication of pneumonic or bubonic plague or it can occur by itself. When it occurs alone, it is caused in the same ways as bubonic plague; however, buboes do not develop. Patients have fever, chills, prostration, abdominal pain, shock, and bleeding into skin and other organs. Septicemic plague does not spread from person to person.

Important questions :A: What should someone do if they suspect they or others have been exposed to plague? Get immediate medical attention: To prevent illness, a person who has been exposed to pneumonic plague must receive antibiotic treatment without delay. If an exposed person becomes ill, antibiotics must be administered within 24 hours of their first symptoms to reduce the risk of death. Notify authorities: Immediately notify local or state health departments so they can begin to investigate and control the problem right away. B: How can the general public reduce the risk of getting pneumonic plague from another person or giving it to someone else? If possible, avoid close contact with other people. People having direct and close contact with someone with pneumonic plague should wear tightly fitting disposable surgical masks. If surgical masks are not available, even makeshift face coverings made of layers of cloth may be helpful in an emergency. People who have been exposed to a contagious person can be protected from developing plague by receiving prompt antibiotic treatment.C:How long can plague bacteria exist in the environment?Yersinia pestis is easily destroyed by sunlight and drying. Even so, when released into air, the bacterium will survive for up to one hour, depending on conditions.D:Is a vaccine available to prevent pneumonic plague?Currently, no plague vaccine is available in the United States. Research is in progress, but we are not likely to have vaccines for several years or more.E: What happen when the rats are killed by plague? The fleas leave the rats and can become parasitic on humans.

Note: Infection with plague or typhus occurs by the infected faeces or contents of a crushed flea entering the skin which has become damaged by scratching. plague diagnosis The first step is evaluation by a health worker. If the health worker suspects pneumonic plague, samples of the patient’s blood, sputum, or lymph node aspirate are sent to a laboratory for testing.

Treatment

As soon as a diagnosis of suspected plague is made, the patient should be isolated, and local and state health departments should be notified. Drug therapy should begin as soon as possible after the laboratory specimens are taken. The drugs of choice are streptomycin or gentamycin. Those individuals closely associated with the patient, particularly in cases with pneumonia, should be traced, identified.

Prevention Attempts to eliminate wild rodent plague are costly and futile. Therefore, primary preventive measures are directed toward reducing the threat of infection in humans in high risk areas through three techniques -- environmental management, public health education, and preventive drug therapy.

Environmental Management

Epidemic plague is best prevented by controlling rat populations in both urban and rural areas. This goal has been reached in the cities, towns, and villages of most developed countries. It has not been achieved in either the rural or urban areas of many developing countries where the threat of epidemic plague continues to exist. Control of plague in such situations requires two things: 1) close surveillance for human plague cases, and for plague in rodents, and 2) the use of an effective insecticide to control rodent fleas when human plague cases and rodent outbreaks occur. Wearing a close-fitting surgical mask also protects against pneumonic plaque infection.

Preventive Drug Therapy

Antibiotics may be taken in the event of exposure to the bites of wild rodent fleas during an outbreak or to the tissues or fluids of a plague-infected animal. For preventive drug therapy, the preferred antibiotics are the tetracyclines, chloramphenicol, or one of the effective sulfonamides.

Sand flea

A sand flea is also known by many other names. also called a beach flea, hop-a-long, no-see-um, biting midge, and punkie or punky. The sand flea is less than 1/8 of an inch (3 mm) long and is often difficult to see. It is a shrimp-like creature in appearance and ranges in color from pale to brownish. The body has seven segments and it has long legs that are used for swimming or jumping. They are known to jump to a height of at least 40 cm and therefore, it is unusual to experience a sand flea bite on upper body parts unless the victim was lying down. The bites are normally found in clusters around the ankles.

Order Anoplura - Sucking Lice

Lice (singular: louse) is the common name for over 3000 species of wingless insects of the order Phthiraptera; three of which are classified as human disease agents. Humans host three different kinds of lice: head lice, body lice , and pubic lice. Lice . Both sexes feed on blood. Lice are affected by temperature changes with a fever or death of their host causing them to seek a new host.

Morphology

They have a leathery surface and are flattened from above (dorsoventrally). The body is divided into: A head, which is small and bears a pair of short antennae, small eyes, and mouth-parts adapted for sucking. A thorax without wings. The 3 pairs of legs are well- developed and terminate in single hooklike clawfor gripping.The last abdominal segment in the female bears a median dorsal genital opening and two lateral blunt gonopods, which clasp the hairs during oviposition.

The life cycle The eggs are laid on hair or clothing and fixed firmly to the host or to clothing by a glue-like substance secreted around the eggs by the female. The egg hatches to release a nymph. The nymph mature after three molts and become adults about 7 days after hatching. Development takes 2-3 weeks.

The three medically important lice are:

Pediculus humanus capitis (head louse).

Pediculus humanus corporis (body louse, clothes louse)

Pthirus pubis (crab louse, pubic louse).

A- Head lice

Pediculus humanus capitis: Head lice infest the head and neck and attach their eggs to the base of the hair shaft. Lice move by crawling, they cannot hop or fly. Head lice are spread by close person-to-person contact. Dogs, cats, and other pets do not play role in the transmission of human lice. Adult head lice are 2.1-3.3 mm in length. has 6 legs (each with claws), and is tan to grayish-white. Females are usually larger than males and can lay up to 8 nits per day. Adult lice can live up to 30 days on a person’s head. The head louse is an ectoparasite whose only host are humans. The louse feeds on blood several times daily and resides close to the scalp to maintain its body temperature. Infestation with head lice is most common among preschool- and elementary school-age children and their household members and caretakers. Head lice are not known to transmit disease; however, secondary bacterial infection of the skin resulting from scratching can occur with any lice infestation.

Life cycle

The life cycle of the head louse has three stages: egg, nymph, and adult. Eggs: Nits are head lice eggs. They are hard to see and are often confused for dandruff or hair spray droplets They are 0.8 mm by 0.3 mm, oval and usually yellow to white. Nits take about 1 week to hatch (range 6 to 9 days). Nymphs: The egg hatches to release a nymph. The nymph looks like an adult head louse, but is about the size of a pinhead. Nymphs mature after three molts and become adults about 7 days after hatching.

, Pediculus humanus capitis

Mode of spread

Getting head lice is not related to cleanliness of the person or their environment..Head lice are spread by direct contact with the hair of an infested person. Such contact can be common among children during play at

• school,home, and elsewhere (e.g., sports activities, playgrounds, camp, and slumber parties). Uncommonly, transmission may occur by: • wearing clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons worn by an infested person; • using infested combs, brushes or towels; or laying on a bed, couch, pillow, carpet, or stuffed animal that has recently been in contact with an infested person.

Medical importance Head lice are not known to transmit any disease and therefore are not considered a health hazard. Pediculosis capitis (also known as Head lice infestation and Cooties) is a human medical condition caused by the colonization of the hair and skin by the parasitic insect Pediculus humanus capitis—the head louse. Head lice infestations can be asymptomatic, particularly with a first infestation or when an infestation is light. Itching (“pruritus”) is the most common symptom of head lice infestation and is caused by an allergic reaction to louse bites. It may take 4-6 weeks for itching to appear the first time a person has head lice. sores on the head caused by scratching. These sores caused by scratching can sometimes become infected with bacteria normally found on a person’s skin. Head lice bites on the nape of the neck

Diagnosis : Close examination of the hair and scalp is necessary to determine head lice infestation

.

Adult male (left) and female (right) head lice

Head louse nits on human hair

Note :Misdiagnosis of head lice infestation is common with dandruf. The diagnosis of head lice infestation is best made by finding a live nymph or adult louse on the scalp or hair of a person.

Treatment

Treatment for head lice is recommended for persons diagnosed with an active infestation. All household members and other close contacts should be checked. Retreatment of head lice usually is recommended because no approved pediculicide is completely ovicidal. To be most effective, retreatment should occur after all eggs have hatched but before new eggs are produced.

Prevention

The following are steps that can be taken to help prevent and control the spread of head lice: Avoid the mode or the ways of transmission (see above) B-Body lice

Adult body louse similar to head louse in shape and nearly the same size it is 2.3-3.6 mm in length. Body lice live and lay eggs on clothing and only move to the skin to feed. Body lice infestations (Pediculosis) are spread most commonly by close person- to-person contact but is generally limited to persons who live under conditions of crowding and poor hygiene (e.g homeless, refugees , victims of war or natural disasters etc). Improved hygiene and access to regular changes of clean clothes is the only treatment needed for body lice infestations.

Life cycle: Similar to P.capitis life cycle

Medical importance.

Note: Only the body louse is known to spread disease.

Pediculus species transmit: • Relapsing (louse-borne) fever Trench fever: caused by Borrelia recurrentis. Infection occurs when the borreliae enter damaged skin following the crushing of an infected Pediculus body louse. The organisms live in the blood of the louse and are not passed in the faeces.

• Epidemic (louse-borne) typhus : caused by rickettsial organisms, which are found in the faeces of the louse. Infection occurs when infected louse faeces are deposited on the skin during or after feeding. Irriration causes the organisms to be rubbed in.

Vagabond’s disease

When body lice infestation is long lasting, heavily bitten areas of the skin can become thickened and darkened, particularly in the mid-section of the body. This condition is called vagabonds disease. Intense itching (“pruritus”) and rash caused by an allergic reaction to louse bites are common symptoms of body lice infestation. As with other lice infestations, intense itching leads to scratching which can cause sores and secondary bacterial infection of the skin. Diagnosis

Body lice infestation is diagnosed by finding eggs and crawling lice in the seams of clothing. Sometimes a body louse can be seen crawling or feeding on the skin.

Treatment

A body lice infestation is treated by improving the personal hygiene of the infested person, including assuring a regular (at least weekly) change of clean clothes. Clothing, bedding, and towels used by the infested person should be laundered using hot water (at least 130°F) and machine dried using the hot cycle.

Prevention

Bathe regularly and change into properly laundered clothes at least once a week; launder infested clothing at least once a week.

Phthirus species

C- Pubic (Crab ) Lice

Crab lice (also known as "crabs," Phthirus pubis, Pthirus pubis, and "pubic lice are parasitic insects notorious for infesting human genitals. The species may also live on other areas with hair, including the eyelashes. They feed exclusively on blood. Humans are the only known hosts of this parasite. P. pubis lives in the hair of the pubic region, axillae, and other parts, but not on the head. Its bite causes irritation and discomfort. Pubic lice infestations (pthiriasis) are usually spread through sexual contact. Lice infestations is found worldwide and occurs in all races and ethnic groups and in all levels of society .

Morphology

Pubic lice are short and crab- like and appear very different from head and body lice. Adult pubic lice are 1.1-1.8 mm in length typically are found attached by strong clawes to hair in the pubic area but sometimes are found on coarse hair elsewhere on the body (e.g- eyebrows, eyelashes, beard, mustache, chest, armpits, etc).

. Pubic Louse - Phthirus pubis

Disease

Pubic (“crab”) lice are not known to transmit any disease. Itching (“pruritus”) in the pubic and groin area is the most common symptom of pubic lice infestation. As with other lice infestations, intense itching leads to scratching which can cause sores and secondary bacterial infection of the skin.

Pubic lice in genital area Pubic lice on eyelashes

Note: Persons infested with pubic lice should be evaluated for other sexually transmitted diseases (STDs).

Diagnosis

Pubic lice infestation is diagnosed by finding a “crab” louse or eggs on hair in the pubic region or, less commonly, elsewhere on the body (eyebrows, eyelashes, beard, mustache, armpit, perianal area, groin, trunk, scalp).

Treatment 1. Wash the infested area; towel dry. 2. Leave medication on hair for the time recommended in the instructions. After waiting the recommended time, remove the medication by following carefully the instructions on the label or in the box. 3. Following treatment, most nits will still be attached to hair shafts. Nits may be removed with fingernails or by using a fine-toothed comb. 4. Put on clean underwear and clothing after treatment 5. Persons should avoid sexual contact with their sex partner(s) until both they and their partners have been successfully treated and reevaluated to rule out persistent infestation. 6. Repeat treatment in 9-10 days if live lice are still found.

Note:Persons with pubic lice should be evaluated for other sexually transmitted diseases (STDs). All sex partners from within the previous month should be informed that they are at risk for infestation and should be treated.

Prevention

Pubic (“crab”) lice most commonly are spread directly from person to person by sexual contact. Pubic lice very rarely may be spread by clothing, bedding, or a toilet seat. Avoid the mode of transmission (see above).

Order Hemiptera – True Bugs

True bugs adults are identified by the X-shaped pattern on their wings and by their piercing sucking mouth. The X-shaped pattern is due to the fore wings in which the anterior half is thickened and the posterior half is membranous. This is called the hemelytron Bugs

:There are two medically important families of bugs

Cimicidae

Triatominae

Cimicidae bugs The Cimicidae family of bugs includes the bedbugs: Cimex lectularius Cimex rotundatus.

Bedbugs (Cimex) Sometimes referred to as "red coats," "chinches," or "mahogany flats", bed bugs, are blood feeding parasites of humans, chickens, bats and occasionally domesticated animals . Bedbugs are small parasitic insects of the family Cimicidae (most commonly Cimex lectularius). Live in the cracks of walls, floors, and wood-work and in the furniture of human dwellings. They emerge at night in search of hosts from which to feed. The bugs suck blood from humans and other warm-blooded animals. Bedbugs are found worldwide .

Morphology

Adult bedbugs are reddish-brown, flattened, oval, and wingless. Bedbugs have microscopic hairs that give them a banded appearance. Adults grow to 4–5 mm in length and 1.5–3 mm wide. Newly hatched nymphs are translucent, lighter in color and become browner as they moult and reach maturity.

Cimex lectularius

Adult bed bug, Cimex lectularius Linnaeus, feeding Life cycle They lay their eggs in dark cracks and it takes several weeks for the nymphs to emerge and develop into mature bugs. Medical importance Bed bugs are suspected carriers of leprosy, oriental sore, Q-fever, and brucellosis but have never been implicated in the spread of disease to humans .Although there is no direct evidence that Cimex bugs are carriers of human disease, their bites are irritating and the bugs may become infected with bacteria and viruses. Hepatitis B has been reported in bedbugs from West Africa, Ethiopia, South America, and elsewhere and there is growing evidence that bedbugs can transmit hepatitis.The bites can also cause an allergic reaction in some people. Note: The first sign of bedbugs may be red, itchy bites on the skin, usually on the arms or shoulders. Bedbugs tend to leave straight rows of bites, unlike some other insects that leave bites here and there. Note: chronic blood sucking cause iron deficiency anaemia.

Straight rows of bugs bites Prevention Remove debris, such as wood and paper trash piles, where these bugs may hide.

Triatominae

The members of Triatominae, a family of Reduviidae, are also known as conenose bugs, kissing bugs (because they often bite around the mouth) , assassin bugs or triatomines. Most of the 130 or more species of this subfamily are haematophagous, (feed on vertebrate blood); a very few species feed on other invertebrates . They are mainly found and widespread in the Americas, with a few species present in Asia, Africa and Australia. Triatomine bugs feed from humans mainly at night. They bite mainly on the face around the mouth and eyes. Triatomine bugs also feed on many wild and domestic animals. The bugs invade houses by flight, often attracted to light. They can also enter human dwellings when the leaves of trees in which bugs are living are used for roofing. The bugs colonize badly made mud houses, living in the cracks of floors and walls.

Morphology

Reduviid bugs measure up to 35 mm in length, are dark coloured, and may show red and yellow banding . winged with a body which is basically divided into: A head which is long and bears a pair of slender antennae, large eyes, and a proboscis containing mouth-parts adapted for biting and sucking. A thorax with two pairs of wings. An abdomen which is large and oval. dorsal view of the “kissing bug

Life cycle

Triatomine bug involves five nymphal stages, each stage requiring a blood meal for its development. The wings are formed during the last two stages. Adults are long lived and can survive for several weeks without a blood meal.

nymphs and adult Triatomine bugs

Medical importance

Triatomine bugs are vectors of South American trypanosomiasis (Chagas’ disease) which is caused by Trypanosoma cruzi,

Class Arachnids

Arachnids are joint-legged invertebrate animals . All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek word meaning "spider". The Class Arachnida are over 80,000 named species, they are united by the possession of eight legs, the lack of biting and chewing mouthparts (food is ingested in most cases as a liquid, though some help is often given the food in becoming liquid by the secretion of, or regurgitating onto or into the food of, digestive enzymes from the stomach. The arachnids differ from the insects in the absence of wings, the presence of four pair of legs in the adult stage, and the fusion of the head and thorax into a cephalothorax in spiders and scorpions. .The head, thorax, and abdomen are fused into a single body region in ticks and mites

The Class Arachnida is divided into 13 subclasses=order. The best known and medically important subclass are.

-Subclass=Order Acarina or Acari contains(Ticks and Mites). -Subclass=Order Araneae (Spiders)

-Subclass= Order Scorpiones (Scorpions)

Basic characteristics of arachnids include four pairs of legs (1) and a body divided .(into two segments: the cephalothorax (2) and the abdomen (3

Order Acarina Ticks

Tick is the common name for the small arachnids in superfamily Ixodoidea and family Ixodidae and aragasidsae that, along with mites, constitute the Acarina. Ticks are ectoparasites (external parasites), living by hematophagy on the blood of mammals, birds, and occasionally reptiles and amphibians. Ticks are vectors of a number of diseases. A tick will attach itself to its host by inserting its chelicerae (cutting mandibles) and hypostome (feeding tube) into the skin. The hypostome is covered with recurved teeth and serves as an anchor. Ticks can be found in most wooded or forested regions throughout the world. There are two well established families of ticks, the Ixodidae (hard ticks), and Argasidae (soft ticks). Both are important vectors of disease causing agents to humans and animals throughout the world.

(Ixodidae (hard ticks

.Morphology

Members of this family Dermacentor, Ixodes,Rhipicephalus and Amblyomma Both sexes are blood suckers .Hard ticks have the capitulum (where the head and mouthparts are located) exposed and easily visible from the top. The upper side of their body also bears a distinctly sclerotized shield or scutum. This structure covers most of the upper body surface in the male tick, but is restricted to a much smaller area (immediately behind the capitulum) in the female. When a female becomes completely engorged with blood, her abdomen increases to many times its normal dimensions and the scutum will then appear to be extremely small in relation to the .body size. Male ticks do not become so large when engorged

Ixodes

Life cycle

Hard ticks have three distinct life stages. Larvae which emerge from the egg have six legs. After obtaining a blood meal from a vertebrate host, they molt to the nymphal stage and acquire eight legs. Nymphs feed and molt to the next and final stage - the adult, which also has eight legs. After feeding once more, the adult female hard ticks lay one batch of thousands of eggs and then die. Only one blood meal is taken during each of the three life stages. The time to completion of the entire life cycle may vary from less than a year in tropical regions to over three years in cold climates.

Medical importance

Among the hard ticks the genera Dermacentor and Amblyomma are medically important as follows:

Bacterial diseases

Rocky Mountain Spotted Fever

The causative agent, Ricketsia rickettsii, is carried by the Brown Dog tick and the Rocky Mountain Wood Tick (the two Dermacentor species in the United States).

Tularemia

This is also carried by the two Dermacentor species. Tularemia is caused by the bacterium Francisella tularensis, which is carried by rodents, rabbits and hares; as a result tularemia is otherwise known as rabbit fever. One of the several ways that humans can be infected is by being bitten by a tick that has acquired the bacterium after biting one of these animals.

Q fever Various farm animals (cattle sheep goats etc) are the primary carriers of the bacterium Coxiella burnetii which causes Q fever. Spread to humans is usually via inhalation of dust containing dried urine, feces etc of infected animals. However, less commonly, the bacterium can be transmitted via the bite of Dermacentor ticks. Ingestion of contaminated milk can also lead to infection.

Ehrlichosis

Human ehrlichiosis is carried by Dermacentor variabilis and by Amblyomma americanum and is caused by a number of bacteria of the Ehrlichia family, in the United States principally by Ehrlichia chaffeensis. These bacteria are small gram- negative organisms that infect leukocytes .

Lyme Disease Lyme disease is caused by the spirochete bacterium, Borrelia burgdorferi, which typically infects small mammals in the northeast and north central United States. It is transmitted to humans by Ixodid black legged ticks (deer ticks).

Protozoal diseases

Babesiosis

Babesiosis is carried by species of Ixodes including the deer tick (Ixodes scapularis) in the north and mid-west of the United States and in other countries, including Europe. Babesia microti is the usual causative organism and is a hemoprotozoan (i.e. it circulates in the bloodstream).

Viral diseases

Crimean-Congo Hemorrhagic Fever

Colorado Tick Fever

Russian spring-summer encephalitis or Taiga encephalitis

Powassan Encephalitis

Tick-Borne Encephalitis

Kyasanur Forest Disease

Louping Ill Virus

Disease caused directly by hard ticks Tick Paralysis In addition to being carriers of disease-causing microorganisms, some ticks (Amblyomma americanum and the two Dermacentor species) can cause tick paralysis. In North America, some tick species secrete a toxin that causes tick paralysis. A person with tick paralysis feels restless, weak, and irritable. After a few days, a progressive paralysis develops, usually moving up from the legs. The muscles that control breathing also may become paralyzed. Tick paralysis can be confused with other acute neurologic disorders or diseases (e.g., Guillain-Barré syndrome or botulism).

Treatment Tick paralysis is cured rapidly by finding and removing the tick . Removal is best accomplished by grasping the tick with curved tweezers as close to the skin as possible and pulling it directly out. The tick's head, which may not come out with the body, should be removed, because it can cause prolonged inflammation. Most of the folk methods of removing a tick, such as applying alcohol, fingernail polish, or petroleum jelly or using a hot match, are ineffective and may cause the tick to expel infected saliva into the bite site. . If breathing is impaired, oxygen therapy or a mechanical ventilator may be needed to assist with breathing.

(Argasidae (soft ticks Morphology Members of this family include Argas and Ornithodoros .In soft ticks, the body has a rather non-descript sac-like shape. The front portion of the body extends forward, above and beyond the base of the capitulum, so that the capitulum is concealed when the tick is viewed from above. Soft ticks have no a scutum on the upper side of the body, and the exoskeleton is rather leathery in texture with a distinctly roughened surface.

Engorged Argaside

Life Cycle The first life stage to come out of the egg, a six legged larva, takes a blood meal from a host, and molts to the first nymphal stage. Unlike hard ticks, many soft ticks go through multiple nymphal stages, gradually increasing in size until the final molt to the adult stage. Some soft ticks pass through up to seven nymphal molts before they become adults. Soft ticks feed several times during each life stage, and females lay multiple small batches of eggs between blood meals during their lives. The time to completion of the entire life cycle is generally much longer than that of hard ticks, lasting over several years. Additionally, many soft ticks have resistance to starvation, and can survive for many years without a blood meal . Medical importance Tick-borne relapsing fever is a rare disease (about 25 cases per year in the United States) and is caused by several spirochete bacterial species of the Borelia family. The transmission agents are soft ticks of the genus Ornithodoros.

Order ACARINA

Mites

In this order the abdomen is unsegmented and fused with the thorax, giving the entire body a more or less sac-like appearance. In many the body is marked by numerous transverse, fine lines, which are so impressed as to appear like the divisions between minute segments. The majority of mites are very small size. Mite is a term commonly used to refer to a group of insect-like organisms, some of which bite or cause irritation to humans. While some mites parasitize animals, including man, others are scavengers, some feed on plants, and many prey on insects and other arthropods. Two genera are medically important: Sarcoptes scabiei (itch mite) and Trombicula

Scabies mites (Sarcoptes scabiei)

The species Sarcoptes scabiei (itch mite) has medically important because it causes scabies when the female mite burrows into the skin to lay its eggs.

Morphology

White disc-shaped dorsally covered by small peg like protuberance and few bristles and there are series of lines across the body so the mite appear striated. The female size range 0.3-0.45 mm and the male 0.2-0.25 mm.The adult have 4 pairs of short cylindrical legs , the first 2 pairs of legs have at its end sucker but in female the posterior 2 pairs end in bristles.There is no clear real head , but short fatty mouth part protrude anteriorly from the body.

Sarcoptes scabiei mite

Life cycle Female select places on the body where skin is thin and wrinkled e.g wrist, elbow, scrotum etc. It digs and eat the stratum corneum layer of the skin and it makes tunnels 1-5 mm/day. It feed on liquid oozing from dermal cells , lay 1-3 eggs /day, the eggs hatch in 3-5 days and larva comes out with 3 pairs of legs, few of these larva succed to burrow into skin or hair follicles make pocket called (moulting pocket) the rest die. After 2-3 days these larvae become nymph with 4 pairs of legs, moulting to become adult and stay in the pocket untill fertilized by the male. Scabies

The word scabies is derived from the Latin word scabere, which means scratch. Colloquially it is the disease known as the seven year itch. It is a contagious skin infection that occurs among humans and animals. Scabies is a common condition found worldwide; it affects people of all races and social classes. Scabies can spread easily under crowded conditions where close body and skin contact is common. Institutions such as nursing homes, extended-care facilities, and prisons are often sites of scabies outbreaks. Human scabies is caused by an infestation of the skin by the human itch mite (Sarcoptes scabiei ). Unlike other mites, scabies mites actually burrow up to 3cm into the skin to lay eggs. The mites are believed to feed on skin and secretions. The entire life cycle (10-17 days for human-infesting scabies mites) is spent on their host. Without a host, they survive only a few days. Scabies can be passed easily by an infested person to his or her household members and sexual partners. Scabies in adults frequently is sexually acquired.

Symptoms

When a person is infested with scabies mites the first time, symptoms usually do not appear for up to two months (2-6 weeks) after being infested; however, an infested person still can spread scabies during this time even though he/she does not have symptoms. If a person has had scabies before, symptoms appear much sooner (1-4 days) after exposure.

Common Symptoms

The most common symptoms of scabies, itching and a skin rash, are caused by sensitization (a type of “allergic” reaction) to the proteins and feces of the parasite. Severe itching (pruritus), especially at night, is the earliest and most common symptom of scabies. A pimple-like (papular) itchy (pruritic) “scabies rash” is also common. Itching and rash may affect much of the body or be limited to common sites such as: between the fingers,-wrist,-elbow,-armpit,-penis,-nipple,-waist,-buttocks,- shoulder blades. The head, face, neck, palms, and soles often are involved in infants and very young children, but usually not adults and older children.Tiny burrows sometimes are seen on the skin; these are caused by the female scabies mite tunneling just beneath the surface of the skin. These burrows appear as tiny raised and crooked (serpiginous) grayish-white or skin-colored lines on the skin surface. Because mites are often few in number (only 10-15 mites per person), these burrows may be difficult to find. They are found most often in the webbing between the fingers, in the skin folds on the wrist, elbow, or knee, and on the penis, breast, or shoulder blades.

Burrows sores Possible other sever complications

The intense itching of scabies leads to scratching that can lead to skin sores. The sores sometimes become infected with bacteria on the skin, such as Staphylococcus aureus or beta-hemolytic streptococci. Sometimes the bacterial skin infection can lead an inflammation of the kidneys called post-streptococcal glomerulonephritis.

Crusted (Norwegian) scabies

Crusted (Norwegian) scabies is a severe form of scabies that can affect the elderly, persons who are immunocompromised, or persons who have conditions that prevent them from itching and/or scratching (spinal cord injury, paralysis, loss of sensation, mental debility). Crusted scabies is characterized by vesicles and thick crusts over the skin that can contain many mites. Itching (pruritus) may be absent in crusted scabies because of a patient’s altered immune status or neurological condition. Because they are infested with large numbers of mites (up to 2 million), persons with crusted scabies are very contagious. Persons with crusted scabies may not show the usual signs and symptoms of scabies such as the characteristic rash or itching (pruritus).

Crusted scabies in person with AIDS

Diagnosis

Diagnosis of a scabies infestation usually is made based upon the customary appearance and distribution of the the rash and the presence of burrows. Whenever possible, the diagnosis of scabies should be confirmed by identifying the mite or mite eggs or fecal matter (scybala). This can be done by carefully removing the mite from the end of its burrow using the tip of a needle or by obtaining a skin scraping to examine under a microscope for mites, eggs, or mite fecal matter . However, a person can still be infested even if mites, eggs, or fecal matter cannot be found.

Treatment

Treatment also is recommended for household members and sexual contacts, particularly those who have had prolonged direct skin-to-skin contact with the infested person. Both sexual and close personal contacts who have had direct prolonged skin-to-skin contact with an infested person within the preceding month should be examined and treated. Products used to treat scabies are called scabicides because they kill scabies mites; some also kill mite eggs. Scabicide lotion or cream should be applied to all areas of the body from the neck down to the feet and toes. In addition, when treating infants and young children, scabicide lotion or cream also should be applied to their entire head and neck because scabies can affect their face, scalp, and neck, as well as the rest of their body. Clean clothing should be worn after treatment. Bedding, clothing, and towels used by infested persons or their household, sexual, and close contacts (as defined above) anytime during the three days before treatment should be decontaminated by washing in hot water and drying in a hot dryer, by dry-cleaning, or by sealing in a plastic bag for at least 72 hours. Scabies mites generally do not survive more than 2 to 3 days away from human skin. Persons with crusted (Norwegian) scabies and their close contacts, including household members, should be treated rapidly and aggressively to avoid outbreaks. Institutional outbreaks can be difficult to control and require a rapid, aggressive, and sustained response.

House dust Mites (Dermatophagoides spp.)

Dust mites live are found in all homes in bedding, carpets, stuffed furniture, old clothing and stuffed toys. They feed on human skin shedding. If droppings of dust mites are inhaled or come in contact with the skin, they may cause asthma and/or eczema symptoms. The mites prefer to live in beds and, because we spend about a third of the day in bed, we inhale large quantities of dust mite allergens.

House mite allergy is a hypersensitive reaction to proteins in the excretion of dust mites. The protein attacks the respiratory passages causing hay fever, runny nose, itching, sneezing,watering eyes and asthma difficulty in breathing. It will aggravate

atopic dermatitis in people who have a tendency to this problem and Infantile eczema

(a skin disease) may get worse..

Demodex

.Demodex mites, are elongated mites with clear cephalothorax and abdomens • the former with four pairs of legs. There are more than 100 species of • Demodex mite, many of which are obligatory commensals of the pilosebaceous unit of mammals. Two distinct Demodex species have been confirmed as the most common ectoparasite in man. The larger Demodex folliculorum, about 0.3-0.4 mm long, is primarily found as a cluster in the hair follicle, while the smaller Demodex brevis, about 0.2-0.3 mm long with a spindle shape and stubby legs, resides solitarily in the sebaceous gland . Both mites have been identified in humans and play a role in three facial conditions: Pityriasis folliculorum, rosacea-like demodicidosis and Demodicidosis gravis. The highly infected sites by this mites are: forehead, area around the orbit, area around the nose, chin and area around the mouth. Infection of the skin by

D. folliculorum is more frequent among females and in the elderly people. The • presence of mites can be determined by microscopic inspection of secretion .from sebum glands and skin surface biopsy

Trombiculid mites (Chigger)

Trombiculidae is a family of mites called trombiculid mites (also called berry bugs; harvest mites; red bugs; scrub-itch mites; aoutas; and, in their larval stage, chiggers). The term chigger is sometimes used to refer to a different animal, the Chigoe flea. Trombiculidae live in the forests and grasslands and are also found in low, damp areas where vegetation is rank such as woodlands, berry bushes, orchards, along lakes and streams, and even in drier places where vegetation is low such as lawns, golf courses, and parks. Chiggers (the larvae of red mites or harvest mites (Trombiculidae) are an important group of ectoparasites affecting humans. They attach to the skin in the ankles, waistline, armpits and perianal area after the host walks through a grassy environment. They pierce the skin near a hair follicle and feed on partially digested skin cells using enzymes in the chigger's saliva. They then drop off the host. And after a few hours an erythematous papule appears that is highly pruritic. The intensity of the eruption depends on the sensitivity of the host and may be followed by fever. In south Asia, chiggers are the vectors for scrub typhus (Orientia tsutsugamushi), a rickettsial disease that can (rarely) be life-threatening.

Scrub Typhus; a rickettsial disease carried by several species of mites of the genus Leptotrombidium. Symptoms include an ulcer-like formation (called an eschar) at the bite site, fever, headache and rash. If left untreated, there is a 30% chance of fatality, although it is readily cured with antibiotics. Occurs in Southeast Asia, Siberia, India, New Guinea, Australia and Japan.

Order Araneida

Spiders

The Spiders differ from other Arachnida in having the abdomen unsegmented and joined to the cephalothorax by a short, narrow stalk. The cephalothorax is also . unsegmented; and the abdomen bears at its end organs for spinning silk

Spiders They are the largest order of arachnids. Spiders are beneficial predators that reduce pest populations (flies, crickets, mites, etc.) in and around homes, yards, gardens, and crops. The venom of most species is not very toxic to humans, usually resulting in no more than a slight swelling, inflammation, or itching sensation. Most spiders, fangs are too small or weak to puncture human skin. Spiders usually will not attempt to bite unless accidentally trapped against the skin or grasped.

Morphology

Spiders have eight legs (four pairs). They have two body regions: a cephalothorax (fused head and thorax) and an abdomen, which are joined together by a narrow waist. Most spiders have six or eight simple eyes in various arrangements. All have a pair of jaw-like structures, the chelicerae, each of which ends in a hollow fang through which venom can be ejected. The tip of the abdomen has a group of small fingerlike spinnerets that produce silk. Young spiders (spiderlings) resemble adults except for their smaller size and coloration.

Life cycle

Spiders lay eggs within a silken egg sac that is often ball-shaped and either hidden in a web, affixed to a surface, or carried by the female. Spiders may produce several egg sacs, each containing up to several hundred eggs. A spider grows by shedding its skin (molting), usually four to twelve times before maturity. Some species of spiders may live for years, but most spiders only survive for one season. All spiders produce silk, which is secreted as a liquid through the spinnerets and hardens on air contact. Spiders use silk for a variety of purposes, such as making egg sacs, capturing prey, holding prey, making shelters or retreats, and transferring sperm during mating. Also, spiderlings extrude silk threads that enable them to be transported by air currents, a process called ballooning.

Medical importance

Spiders are predators that typically feed on living prey. They produce venom that is poisonous to their normal prey of insects, mites, and other small arthropods. Venom is injected through the hollow fangs to immobilize the prey and begin the digestion process. The most common poisonous spiders known in the world are widow and violin spiders.

Widow Spiders

The widow spiders belong to the genus Latrodectus . There are five species found in North America north of Mexico. The black widow for many years was considered to be a single species but since is now recognized to be represented by three species, which are very similar in appearance and habitat. These three widow spiders are the Southern black widow Latrodectus mactans , L. hesperus, and the L. variolus . The female L. mactans (black widow) size 13mm the male smaller 6 mm, sometimes called the hourglass, shoe-button, and po-ko-moo spider, it is the most dangerous species in th USA. It has dark brown or black thorax and legs. The widow spiders are the most notorious of all spiders. L. geometricus , the brown widow is found throughout Africa. The venom, a neurotoxin, is highly virulent in all the widow spiders. Some report that the widow spiders are aggressive but observations shows that they are very timid and have no instinct to bite humans. Most deaths in the United States attributed spider bites are caused by the widow spiders, rarely is the brown recluse's bite lethal. The black widow spider is nocturnal. The best time to observe their presence in an area is a night.

Brown recluse spider or violin spider, Loxosceles reclusa,

Brown recluse spiders are usually between 6–20 mm (¼ in and ¾ in), but may grow larger. While typically light to medium brown, they range in color from cream- colored to dark brown or blackish gray. These spiders usually have markings on the dorsal side of their cephalothorax, with a black line coming from it that looks like a violin with the neck of the violin pointing to the rear of the spider, resulting in the nicknames fiddleback spider, brown fiddler or violin spider. Most spiders have eight eyes; recluse spiders have six eyes arranged in pairs with one median pair and two lateral pairs. The abdomen is covered with fine short hairs that give it the appearance of soft fur.

Brown recluse spider Arachnidism

Arachnidism is a medical term used to describe the symptoms and pathology produced by the venom of the poisonous spiders, i.e. the black widows and the brown recluse (violin spider). It may be either a systemic reaction or a necrotic local lesion. The black widow spider (Latrodectus mactans) characteristically produces a systemic reaction because its venom is a neurotoxin. In contrast, the brown recluse spider (Loxosceles recluse) venom produces a necrotic local lesion at the site of the bite but can cause systemic reaction such as DIC(disseminated intravascular coagulation). Necrotic arachnidism is mainly reported in cases having been due to envenomation by Loxosceles recluse, All black widow and most brown widow spiders are poisonous for humans. Emergency medical first aid is indicated with the bite of any of these spider bites, especially the black widow because of its neurotoxic envenomation.

Diagnosis There is no way to identify a particular spider on the basis of its bite mark. Widow spiders are recognized by a red or orange hourglass-shaped marking on the abdomen. Brown spiders have a violin-shaped marking on their back. However, these identifying marks can be difficult to discern, and the spider is rarely retrieved intact, so the diagnosis is usually uncertain and based on symptoms.

Black Widow Spider Bite

Order Scorpiones (Scorpions)

Scorpions Scorpions have long been of interest to humans primarily because of their ability to give painful and sometimes life threatening stings. Found on all major land masses other than Antarctica, and in many different habitats; from high on mountains at elevations up 5 500 metres to the sea shore, from the driest deserts to tropical rain forest .and from 40 metres up to 800 metres below ground in a cave. Most species stay within 1 metre of their burrows and some may spend as much as 97% of their lives inside their burrows.

Scorpions are venomous arthropods in the class Arachnida, relatives of spiders, mites, ticks, and others. There are currently 1400 recognized species of scorpions worldwide.

Morphology

Scorpions are characterised by a metasoma (tail) comprising six segments, the last containing the scorpion's anus and bearing the telson (the sting). The telson, in turn, consists of the vesicle, which holds a pair of venom glands and the hypodermic aculeus, the venom-injecting barb. The abdomen's front half, the mesosoma, is made up of six segments. The first segment contains the sexual organs as well as a pair of vestigial and modified appendages forming a structure called the genital operculum. The second segment bears a pair of featherlike sensory organs known as the pectines; the final four segments each contain a pair of book lungs. The mesosoma is armored with chitinous plates, known as tergites on the upper surface and sternites on the lower surface. Scorpions have mouthparts called chelicerae, a pair of pedipalps, and four pairs of legs. The pincer-like pedipalps are used primarily for prey capture and defense, but are also covered with various types of sensory hairs. The cephalothorax is covered above by a carapace (or head shield) that usually bears a pair of median eyes and 2 to 5 pairs of lateral eyes at its front corners (a few cave and litter-dwelling scorpions are completely eyeless). The "long-tailed" African Scorpion (Hadogenes troglodytes) reaches a length of over 8 inches, and is probably the longest scorpion in the world. Some of the African and Asian Emperor Scorpions routinely reach (and probably exceed) 7 inches. The largest scorpions in the United States are members of the genus Hadrurus (giant desert hairy scorpions), obtaining a length of about 5 inches. Giant desert hairy scorpions also occur in Arizona. All the deadly species belong to the family Buthidae. Scorpion Stings

Scorpion Venom

The venom of scorpions is used for both prey capture, defense and possibly to subdue mates. All scorpions do possess venom and can sting, but their natural tendencies are to hide and escape. Scorpions can control the venom flow, so some sting incidents are venomless or only mild envenomations. Scorpion venoms are complex mixtures of neurotoxins (toxins which affect the victim's nervous system) and other substances; each species has a unique mixture. Few species have venom potent enough to be considered dangerous to humans. The world's most dangerous scorpions live in North Africa and the Middle East (species in the genera Androctonus, Buthus, Hottentotta, Leiurus), South America (Tityus), India (Mesobuthus), and Mexico (Centruroides). Some studies suggest typical mortality rates up to about 4% in hospital cases, with children and the elderly being most susceptible. Death by scorpion sting, if it occurs, is the result of heart or respiratory failure some hours after the incident. During the 1980's Mexico averaged about 800 deaths each year. However, in the past 20 years there have been no reported fatalities in the US due to scorpion stings.

Common symptoms

The sting is painful, sometimes causing numbness or tingling in the area around the sting. Serious symptoms are more common in children and include

• Abnormal head, eye, and neck movements • Increased saliva production • Sweating • Restlessness Some people develop severe involuntary twitching and jerking of muscles. Breathing may become difficult.

Treatment Placing an ice cube on the wound reduces pain. A cream or ointment containing an antihistamine, an anesthetic, a corticosteroid, or a combination of them is often useful. Stings that result in serious symptoms may require the use of sedatives given intravenously. antivenom rapidly relieves symptoms, but it may cause a serious allergic reaction or serum sickness. The antivenom is given only if symptoms are severe. In areas of the world where scorpions are more poisonous, such as Turkey, the Middle East, and India, stings are treated with drugs and methods that reduce symptoms and complications. an alpha-adrenergic blocking drug, is sometimes used. Antivenins to specific scorpion venoms are available, but their effectiveness has not been proven.

Class Myriapoda

The members of this class are air-breathing Arthropods, in which the head is distinct from the thorax, and the thorax and abdomen form a continuous region, with from six to two hundred segments, each bearing a pair of legs. The head bears a single pair of antennae. . Nearly 13,000 species of arthropod are classified in the Myriapoda. they range in size from nearly microscopic to 30 cm in length. The thousand-legged worms, as they are commonly called, are well-known and generally feared creatures. Most myriapods live in humid environments, and can be found in soils, in leaf litters, or under stones and wood. Many species possess , specialized glands that secrete foul- tasing compounds and thus function in defense.

There are four orders of myriapods; Two of them, the Symphyla and Pauropoda, consist of tiny arthropods living in leaf litter and soil; both superficially resemble centipedes. The other two principal orders are Diplopoda(millipedes) and The Chilopoda (centipedes). Chilopods have only one pair of legs per body segment. They are predators; the first pair of appendages on the trunk are modified into a pair of claws with poison glands, which centipedes use to capture prey (usually other arthropods). The bite of large centipedes can cause humans some pain and discomfort, although there are no authenticated cases of human fatalities from centipede bites.The millipedes have been incriminated as hosts of the cestode H. diminuta, and some produce vesicating agents.

Class Crustacea The members of this class are aquatic Arthropda, which breathe by true gills. They have two pairs of antennae and at least five pairs of legs.The most familiar Crustacea .are the Cray-fishes, the Lobsters, the Shrimps, and the Crabs. Cray-fishes

They are invertebrates with hard shells (exoskeleton) and segmented bodies with pairs of jointed appendages. The aquatic crustacean contain two medically important species, Decapoda (literally "ten footed") are an order of crustaceans , including many large crustacean familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers, species of fresh-water crabs and crayfish are second intermediate hosts of the lung fluke P. westermani. Fresh-water prawn and land crab harbor the infective rat lung worm larvae (Angiostrongylus) that infect man brain. Copepods meaning (oar feet) small 2-3 mm shrimp-like aquatic crustaceans , graceful, symmetrical animals with the head and two thoracic segments fused into a cephalothorax, and a slender abdomen 3 to 5 segments ,are inhabitating all types of aquatic (fresh, brackish and sea water) . Cyclop are intermediate hosts of quinea worm D.medinensis, the cestode D. latum and the nematode G. spinigerum.Diaptomus .species are hosts of D.latum

Cyclop

The Phylum Pentastoma

From the Greek Pente for five and Stoma for mouth.

The Pentastoma, or Pentastomida are a smallish phylum with just over 100 species know to science. All known species are parasites of the respiratory tracts of vertebrates in the adult form. Ninety percent of the known pentastomids use reptiles as their hosts, the remaining ten percent use birds and mammals as their primary hosts. For example Linguatula serrata is a parasite of dogs, Foxes and Wolves, while Reighardia sternae lives in the air sacs of Gulls and Terns. Pentastomids, or tongue worms, are small animals, ranging in length from less than 1 cm (just under 0.5 of an inch) to almost 14 cm (5.5 inches). They are worm-like in appearance, as their common name suggests, and the adults possess four pairs of hooks near the mouth. Pentastomids do in fact only have one mouth, the claws are used to hold onto the host. Pentastomids, like most parasites, have an adult morphology dedicated to reproduction. They have no circulatory or excretory system, no respiratory organs and a very simple and often greatly reduced nervous system. They have a straight through gut which is adapted to sucking up the hosts blood, or in the case of Linguatula mucous. The body is covered in a thin cuticle but they have practically no sensory apparatus. Internally the body is a pseudocoel. Pentastomids are gonochoristic, meaning the sexes are separate and distinct. Fertilisation is internal and involves copulation. An adult female will live for several years and during this time she will produce millions of eggs. In most species these eggs are released into the hosts alimentary system where they pass out of the animal with its faeces. The exception to this is Linguatula where some or all of the eggs may be sneezed out through the nostrils. Some of these eggs will later be eaten by the secondary host, normally an insect or small mammal. In the secondary host the larvae go through two instars before becoming encysted somewhere in the hosts body. When the secondary host is eaten by the primary host the 3rd stage larvae emerge from the cyst, climb out of the stomach and up the oesophagus to infect the hosts lungs. Most species feed on their hosts blood through the walls of the lungs. Linguatula is unusual in that it infect the nasal cavities and does not feed on its hosts blood. Linguatula serrata will occasionally infect humans, in India and the Middle East where it is known as nasopharyngeal pentastomiasis or halzoun.

Some common terms and words used in entomology meanings

Arbovirus -a virus spread by arthropods. Arbovirus is short for arthropod-borne virus. They are most commonly spread by blood-sucking insects such as mosquitoes. Arboviruses can cause minor illnesses such as mild fevers and rashes or they can cause potentially fatal illnesses such as encephalitis (inflammation of the brain).

Class -a division of the animal kingdom lower than a Phylum and higher than an Order. For example, the "Class Insecta" is a division of the Phylum Arthopoda.

Cuticle -the external skeletal structure of the insect body. The cuticle is secreted by the epidermis, is composed of chitin and protein and consists of several differentiated layers.

Family -in zoological classification, a level of the taxonomic hierarchy below the Order and above the Genus. All zoological Family names end in the suffix '-idae'

Genus -an assemblage of Species agreeing in one character or a series of characters. It is usually considered arbitrary and opinionative grouping, though some consider it a natural assemblage.

Hemimetabolous - insects with incomplete metamorphosis, where the individual develops with gradual changes in size and shape. There are three distinct stages in the development of a hemimetabolous insect: egg, nymph (juvenile of any instar) and adult.

Hermaphrodite -an individual that possesses both male and female reproductive organs.

Holometabolous - insects with complete metamorphosis, where the body form changes abruptly. Holometabolous insects have four distinct forms during their life cycle: egg, larva, pupa and adult. Instar - the growth stage between two successive moults.

Larva -an immature stage of a holometabolous insect that is morphologically distinct from the adult form. The larval stage of development follows the egg stage and precedes the pupal stage.

Metamorphosis -the physical transformation an insect undergoes during successive stages of development

Moult - the process by which insects shed elements of the integument during growth.

Nymph - an immature insect after emerging from the egg. This term usually refers to insects in which there is incomplete metamorphosis (see hemimetabolous).

Omnatidium (pl. Ommatidia) - the basic visual element that forms the compound eye. The omnatidium is composed of a lens, cone, rhabdom and pigment cells. The size, shape and number of ommatidia that form the compound eye vary among species. View image

Order - one of the primary taxonomic divisions below Class level and above Family level. In Class Insecta, the division of Order was originally based on wing structure with ordinal names usually ending in -ptera e.g. Order Diptera.

Ovipositor -an egg-laying tube of the female insect's abdomen. The morphology of the ovipositor varies among species: it may be fixed and rigid in length or it may be flexible and telescopic. The ovipositor is not present in all insect species.

Parthogenesis - reproduction without fertilization. Individuals develop from an unfertilised egg. Phylum -a category used in biological classification, below Kingdom level and above Class level.

Pupa -the inactive state between larva and adult in holometabolous insects. During pupation, the larva transforms into the adult.

Species -the basic unit of biological classification. Generally defined as an aggregation of individuals similar in appearance and structure, mating freely and producing young that themselves mate freely and bear fertile offspring. Abbreviated to sp. for one species and spp. for two or more species.

Vector -any organism which transports or transmits a parasite to a host. In medical entomology, a vector is an arthropod which carries disease producing organisms to a vertebrate host.

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