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Parasitology is the study of parasites , their hosts , and the relationship between them

Definitions

What are Parasites

An organism that is entirely dependent on another organism referred to as the host for all or part of its life cycle and metabolic requirements

What is Parasitology

This is the area of biology concerned with the phenomena of dependence of one living organism on another. It is an aspect of symbiology which deals with the study of Parasites Medical parasitology One of the largest fields in parasitology, medical parasitology is the study of those parasites which infect humans Veterinary parasitology The study of parasites which cause economic losses in agriculture or aquaculture operations, or which infect companion

Tropical parasitology: study of parasites that affect man and animals in the Tropics

Types of Parasites

Site: Ectoparasitesexternal parasites. Live temporarily or permanently on the surfaces of the host (skin, feathers, gillsetc). E.g. ticks, lice,etc. the occurrence of ectoparasites especially is called .

Endoparasites internal parasites. Live inside or within the host tissues and organs. Endoparasites that live within the cells of the host tissues are called Intracellular parasites e.g. malarial parasites (plasmodium species). Those that live in tissues but not within the cells are called Extracellular parasite. Those living in the host lumen such as the gut, circulatory blood and lymph vessels, the respiratory and urino genital tracts are called coelozoic parasites, while those living in the tissues of the host are called histozoic.

Size: Microparasites small, unicellular and multiply rapidly within the host often inside cells e.g. protozoans.

Macroparasites-large, multicellular and do not have direct reproduction within its vertebrate host. E.g helminthes

Others

Obligatory/obligate parasite-are absolutely dependent on the host and are incapable of an alternative or independent existence.

Facultative-are opportunistic parasites which can live a nonparasitic existence and can survive for a limited period within another organism. They are capable of both free and parasitic existence E.g. S.stercoralis. Host

A host is the nonparasitic member in a parasitic association. It harbours the parasite and provides the nourishment and shelter to the parasite.

Types: Definitive Host: Harbours the adult parasite, the most highly developed form of a parasite or where the parasite replicates sexually

Intermediate host: This is the host which alternates with the definitive host and harbours the larval or asexual stages of a parasite. Some parasites require two intermediate hosts for the completion of their life cycle.

Reservior: It is a host that harbours the parasite and serves as an important source of infection to other susceptible hosts.

Dead end Host: is the host in which the parasite cannot be further transmitted

Vector: A vector is an agent, usually an insect that transmits an infection from one human host to another. They transmit the infective stage of parasites to the other.

PHYLUM NEMATODA

In Tropical Africa, are of particular importance because they cause great morbidity, mortality and economic loss. Many of them are freeliving in soil, freshwater and marine habitat, while many others have adapted the parasitic mode of life; parasitizing plants and animals.

Morphology and Anatomy

There are 3 major features which are of profound impact on the form, function and mode of life of nematodesa. Body wall,pseudocoelom. and. hydrostatic skeleton. b. The reproductive system.c. The digestive system

Body wall, pseudocoelom and hydrostatic skeleton a.Body wall: This is made up of a cuticle , hypodermis and longitudinal muscle layer .

Cuticle :This is secreted by the epidermis. It can be smooth or covered with structures such as spines, bristles, warts, papillae, striations etc. The arrangements and positions of these structures are of taxonomic importance. The cuticle covers the entire external surface and also lines the buccal cavity, pharynx, rectum, cloaca, vagina and excretory pore. The cuticle is responsible in part for allowing the invasion of hostile environments such as dry terrestrial soils and the digestive tracts of hosts. This is because it helps to reduce the permeability of the body wall. The terrestrial or parasitic nematodes usually have dense fibrous inner layer of the cuticle while most of the freeliving marine and freshwater lack this inner layer. As the grows, it sheds its cuticle and grows a new one through a series of 4 moults during its lifetime.

.The Hypodermis This is a layer lying beneath the cuticle which it secretes (or the basal lamina). It has 4 projections which make up the hypodermal cords. The cords project into the pseudocoel. The cords run longitudinally dividing the body wall musculature into 4 quadrats the dorsal and ventral cords carry the longitudinal nerve cords while the 2 lateral cords contain the excretory canals.

Longitudinal muscle layers Next to the hypodermis is a relatively thick muscular layer.The muscle layer is made up of single cells whose cytoplasm is differentiated into a contractile portion with myofibrils and a cytoplasmic or non contractile portion. These cells are arranged in rows and the number of rows per quadrant and the shape and disposition of the contractile portion are of value in separating and recognizing types of nematodes.

The Pseudocoelom

The body cavity is not a true coelom It is a Pseudocoelom containing a fluid under great hydrostatic pressure/ The fluid is the haemolymph which functions in the transport of solutes from one tissue to the other.

Hydrostatic skeleton

With no skeletal structures, nematodes rely on the body fluid in the pseudocoelom which being under great internal pressure serves as a Hydrostatic skeleton against which the muscles of the body wall act to bring about movement.

Other specialized structures of the Body surface

Lips: The mouth is usually surrounded by lips and also array of sensory bristles or papillae. In the primitive, freeliving nematodes, the number is six but in parasitic species the number varies from 0 to three.

Amphids: These are chemoreceptors found as a pair on each side of the cephalic end. These are mostly found in the freeliving species but in reduced form on many parasites.

Phasmids: These are sensory organs. Also found in pairs at the terminal end behind the anus.

The reproductive System. The great success of nematodes as parasites is derived mainly from their ability to maintain reproductive efficiency with little morphological specialization.

Male system

The male system is usually single (single testis). It is made up of a long threadlike testis whose coils surround the intestine and fills up most of the body cavity not occupied by the intestine. Two types of testes are recognized among nematodes the telogonic type in which the proliferation of germ cells occurs only at the blind end of the elongate testis and the hologonic in which germ cell proliferation occurs along the entire length of the testis. Most species have spicules whose function is to keep the vulva open during copulation so that sperm can be injected into the female vulva against hydrostatic pressure. The sizes and shapes of the spicules vary among species and so are useful taxonomic features.

Female system Most nematodes have 2 ovaries(didelphic). The ovary is threadlike and forms many coils around the intestine and reproductive system, filling most of the body cavity. Different terms used to describe the number and arrangement of reproductive system:

1. Monodelphic: where only one ovary and uterus are present. 2. Didelphic-two ovaries and two uteri are present 3. Polydelphic-more than two ovaries and uteri.

Classification

Nematodes parasites can be classified :

1. Based on location of the adult in the body 2. Based on mode of infection 3. Systemic (Zoological) classification.

Location of nematode Conjunctiva Mesentery Lungs Subcutaneous Small Large Lymphatic tissue intestine intestine system - Strongyloides Loa loa Trichuris Wucheraria stercoralis lumbricoides trichiura bancrofti Medinensis volvulus Ancylostoma Entorobius duodenale vermicularis ozzardi

Trichinella spiralis

Strongyloides stercoralis

Mode of infection By ingestion By cutaneous By blood sucking penetration insects A.lumbricoides N. americanus Filaria. T. trichiura A. duodenale E. vermicularis S. stercoralis D. medinensis T. spiralis

Systemic (Zoological) classification.

A lot of controversy about classification of nematode into higher taxa. Division into two classes Aphasmidae and Phasmidae based on presence or absence of the caudal sense organs the phasmid is widely accepted. Recently, the phylum has been divided into two classes, and Adenophorea depending on the nature of the excretory system. According to Kampfer et al (1998), the Phylum is divided into two classes. Class Adenophorea (=Aphasmida) and Class Secernentea (Phasmida) Class Adenophorea Have cephalic chemoreceptors called amphids Lack caudal chemoreceptors called Phasmids. Excretory system is simple or poorly developed. At times absent. OrderTrichocephalida family Trichinellidae.e.g Family Trichuridae E.g. Class Secernentea Ha ve cephalic chemoreceptors called Amphids, though poorly developed Have caudal chemoreceptors called Phasmids Excretory system complex in some with cuticulized duct and well developed collecting tubules Order Rhabditada . Family Strongyloididae.e.g. Strongyloides stercoralis Order family Ancylostomidae.e.g. Order family .e.g. Order family .eg. enterobius vermicularis Order SuperFamily family .e.g. Wucheraria bancrofti, , , Loa loa, etc

Characteristics, lifecycle, morphology of these nematodes Order Trichocephalida Family: Trichinellidae Species: Trichinella spiralis

Morphology 1. lack of spicules in males, single gonad 2. size it is the smallest human nematode 3. the whiplike characteristic is not marked instead the body merely tapers towards the anterior end 4. females are ovoviviparous

Life cycle Th e life cycle is passed in one host only. However the larvae and adults develop in diff organs of one . The adult live in the intestine of man and other suitable host (rat, pigurban cycle, hyenas, leopards, jackalssylvatic cycle in tropics). After copulation. The females burrow into the mucosa and submucosa where being ovoviviparous, produce live larvae (about 1500). The larvae penetrate into the blood stream which distributes them to various organs of the body. They tend to settle in skeletal muscles (eg muscle of diaphragm, jaws, tongues etc). Here they penetrate individual muscle fibres where they grow up to 10 times their original size. During this period, they begin to coil forming the characteristic spiral. Host tissue reactions form a lemonshaped cyst around the larva which is now known as encapsulated larva . Within the cyst, the larva can survive for several months or years and still be viable. However, after about 6 to 18 months, calcification of the cyst and later of the larva themselves set in. Infection occurs when infected muscle is consumed by a suitable host. The larvae are released in the duodenum and develop rapidly, reaching maturity in only 40 hrs. In man, this is the dead end of the infection. T.spiralis however is maintained in the nature by any of these cycles a. pig to pig b.rat to rat c. feral cycle involving wild rodents and various carnivores.

Diagram

Diagnosis Trichinella infection is asymptomatic. Eggs or larvae are not detected in faecal samples. But there are some diagnostic techniques for detecting encapsulated larvae in the muscles: 1. Xray examination: may show the presence of calcified cysts in the muscles 2. Muscle biopsydigesting the biopsy specimen in enzymes and recover the larvae by seb=dimentation in a tube 3. Xenodiagnosismuscle biopsies are fed to lab rats and the presence of infection is confirmed if larvae developed in the muscles of the rat.

Order: Rhabditidae Family: Strongyloididae Species: Strongyloides stercoralis The order has species in which freeliving and parasitic generations alternate in the life cycle. Morphology 1. The parasitic females are parthenogeneticproduce offsprings without being fertilized by the male. The parasitic females are slender and have oesophagus which are almost half the length without an end bulb. 2. The freeliving females are stout and have a rhabditiform oesophagus with an end bulb 3. Freeliving males are smaller than females with rhabditiform oesophagus and two spicules

Eggs Oval, transparent, thin shelled Life cycle The life cycle is very complex. 3 diff cycles can be recognized. Man is the only host. The infection is acquired when man walks barefooted on the soil contaminated with faeces. 1. The Homogonic development The parthenogenic females produce eggs which hatch in the mucosa into rhabditiform larvae. These larvae are passed out with the faeces. They develop into filariform larvae in the soil. These are the infective stage gaining entry into man by penetrating the skin and embarking on larval migration (bld streamheart lungsalveolitracheamouth cavity and swallowed into the stomach). When they get to the intestine, they develop into adulthood. 2. The Heterogonic cycle Here, the rhabditiform larvae in the soil develop into freeliving sexually mature males and females which mate and produce eggs (in the soil). These eggs hatch into rhabditiform larvae which moult into filariform larva (still in the soil), these can either infect man by penetration (as in the direct cycle above ) or develop into freeliving adults again. Successive generations of freeliving adults can be produced in this way, thus increasing the number of larvae available which are capable of infecting man . 3. Auto infection Here, the rhabditiform larva moult into the filariform larva within the intestine and this without passing out of the body, reinfects man by penetrating the intestinal mucosa or the perianal area, proceeding on larval migration before coming back to the intestine to grow to maturity.

Diff btw Rhabditiform and filariform larvae Filariform larvae are the skin penetrating infective forms of the parasite. They are longer and more slender than the Rhabditiform larvae. Rhabditiform larvae are developed directly from the gravid females. Rhabditiform larvae have short mouth and double bulb oesophagus while the filariform larvae have short mouth and cylindrical oesophagus. Diagram

Diagnosis Stool examination : diagnosis is by demonstrating Rhabditiform larvae in fresh stool.

Hookworms About 5 families of medical importance. One of the families is family Ancyclostomatidae. Species include Necator americanus( 1st identified in USA thus referred to as America murderer, necator means murderer and Ancyclostoma duodenale w hich are very prevalent. Morphology 1. derived their names from the fact that the anterior end of the body is curved dorsally, giving the a hooklike appearance 2. Males are distinquished from females based on prominent post copulatory bursa diagram

3. Adult worms are small, grayish white or brown, cylindrical worms. N.americanus is generally smaller than A duodenale.

Diffs btw N americanus and A duodenale A. duodenale N. americanus

size Larger and thicker Smaller and thinner Anterior end Bends in the same Bends in the opposite direction as the body direction of the body curvature curvature Copulatory bursa Dorsal ray is single. Total Dorsal ray is split from number of rays is 13 the base. Total number of rays is 14 Vulva opening situated behind the middle Situated in front of the of the body middle of the body

Buccal capsule six teeth, four hooklike on Four cutting plates, ventral surface and two two each on ventral knoblike on dorsal surface and dorsal surfaces

Diagram

Life cycle Life cycle is direct. Eggs are passed out in faeces. If the eggs are deposited on favourable soil, hatch into the 1 st stage rhabditiform larvae (btw 2448 hrs). By the 3rd day, the larvae moult to the second stage still rhabditiform larvae which continues to feed on bacteria and organic debris.By the 5 th day, the larvae moult again to produce the 3 rd stage larvae. This is the filariform larva infective stage which does not feed but relies on food reserves in the intestine. They are found on the top 15mm of moist soil.Since they are sensitive to dessication and freezing, they undertake vertical migration up and down in the soil depending on the moisture content, temperature of the soil. Can survive for weeks under ideal condition. Human infection is usually through the skin of the feet, hands, buttocks etc areas in frequent contact with the soil. By mechanical and lytic action, the larvae migrate through the epidermis into the dermis and subcutaneous tissue. From the deeper tissue embark on larval migration into venules and lymphatic vessels where they are carried to the right side of the heart and then to the capillary , lungs, alveoli to the pharynx swallowed down the digestive tract to the small intestine. In the small intestine, the larvae undergo a 3 rd moult to become 4 th stage larvae. These attach to the villi and undergo the final moult to become adults.Male fertilizes females and eggs are produced in about 6 weeks and the cycle is repeated. Diagram

Laboratory diagnosis Demonstration of eggs in faeces.Demonstration of adult worm in stool. Indirect method by blood examination to reveal microcytic, hypochromic anaemia and eosinophilia.

ORDER ASCARIDIDA Family:ASCARIDIDAE Species: Ascaris lumbricoides This is the most widespread and commonest nematode parasite of man in tropical Africa. Ascaris lumbricoides has been recognized in man and in pigs Morphology : Are large stout nematodes.Femalesare long, males are smaller with tightly curled posterior end. Diagram

Genital openingsvulva of female is located in the anterior third of the body. Male has a cloacal opening at the posterior end, bearing a pair of simple spicules of equal length. Males also have papillae before and after the anus(pre and post) while females have post anal papillae. Mouthsurrounded by 3 lips. . Diagram Egg : Egg is oval or rounded,. Fertilized and unfertilized eggs have double shell. Life cycle : Life cycle is direct. Man is the only known definitive host of A.l umbricoides. Unembryonated eggs are laid(not infective). Embryonation takes place outside the body under suitable conditions of temp, .moisture content and oxygen tension of the soil to produce the 1 st stage larva coiled within the egg shell in 913 days after passage of the egg. The 1st stage larva moults (1 st moulting) within the egg shell into the 2 nd stage larva (rhabditiform infective larva).3 weeks after the passage of the egg ,Man becomes infected by swallowing an egg containing the 2 nd stage larva (in food, drink or raw vegetables). Hatching takes place in the duodenum where the eggshell is softened by digestive juice in the duodenum. Larval migrationThis is the most remarkable feature of the life cycle. The larvae penetrate the gut wall and enter the blood circulation and the embark on a migration through the liver to the heart and to the lungs through the pulmonary circulation. They break from the capillaries into the alveoli, then to the trachea, to the pharynx and are swallowed back into the stomach and then to the intestine where they develop into adulthood

Diagnosis :Worm when passed in faeces after treatment Eggs fertilized eggsround or oval in shape, floats in saturated salt solution, unfertilizedelliptical, does not float in saturated salt solution

ORDER: OXYURIDA FAMILY:OXYURIDAE SPECIES: Enterobius vermicularis (pin worm) Morphology: 1. Females 813 mm, males 25 mm in length 2. Mouth is surrounded by 3 lips 3. Muscular end bulb pharynx 4. malescurled tail and single spicules 5. Adults live in caecum and large intestine of man.

Life cycle Gravid females migrate down the large intestine through the rectum and lay their eggs in the perianal region at night. After laying about 10,000 eggs the female dies. The sticky and embryonated eggs become infective within 6 hrs. There are 3 means of transmission 1. When infected children scratch their perianal region due to itching, the eggs get lodged in the fingers. Infection occurs when the fingers convey the eggs to the mouth. 2. At times, some eggs hatch in the perianal region and the larvae enter through the anus and migrate up the caecum where they reach maturity. This is known as retroinfection. 3. The eggs which are light can become airborne and disperse. These can be inhaled and subsequently swallowed or can hatch inside the nostril. Also during nosepicking, they could be transferred to fingers and later passed into the mouth and swallowed. Diagnosis Eggs cannot be detected in faeces. Best diagnosis is by cellophane tape swab(attachment of a piece of cellophane to perianal region overnight). Then examined for eggs under the microscope.

Order: SPIRURIDA FAMILY:DRACUNCULOIDIDAE SPECIES: Disease: or guineaworm Morphology: lips are absent. Malesrarely seen,1229x0.4mm,4 pairs of pre anal and 6 pairs of postanal papillae, a pair of spicules. Femalesone of the longest nematodes, 50 100cm with thickness of about 1.0mm. Lifecycle Lifecycle is completed in 2 hosts. A.Definitive hoshostt is man. The worm resides in the sub cutaneous tissue. B. The intermediate host are CyclCyclopsops in which the embryosembryos undergo developmental changes before they become infective to man. Life cycle: When gravid, the female(up to 50 to 100cm long)migrlong)migratesates to the superficialsuperficial subcutaneous tissues, usually in the legs and feet. Here it induces the formatiformationon of a blister which causes intense itching. This blister eventualeventuallyly bursts forming an ulcer. When immersed in cold water the anterior end of the worm is extruded through a hole in the ulcer, releasing thousands of larvae in a milky discharge from its ruptured uterusuterus into the water. When removed from the water, the ruptured part of tthehe worm dries up, sealingsealing off the remaining larvae in the uterus. Subsequent reimmersreimmersionion triggers off a further discharge of larvae, a process which is completed in 2 to 4 weekweeks,s, by which time the empty shell of the worm is ejected. The 1 st stage larvae swim freely in the water and have a leleasease of life of 4to7 days.days. Subsequent development depends on in gestion by intermediate hosts which are various species of freshwater copepods cyclops.. Once inside the stomach of the Cyclops, thethe larva penetrates into the haemocoel where it moults twice to become the 3 rd stage larva which is the infective stage. Man b ecomes infected by drinking water containing CyclopCyclopss harbouring 3rd stage infective larvae. Although the Cyclops are kikilled,lled, the larvae survsurviveive and are activated by the dilute hydrochloric acid in the ststomachomach to escape fromfrom the dead Cyclops and eventually penetrate through the intestinal wall.The worms embembarkark on larval migration from the intestine to the sub cutaneous tissues via the lymphatic systsystem.em. Adult worms emerge after about 4 months, copulation takes place after which the adult mmaleale dies and become encysted and the female migrate towards the extremiextremities(whichties(which are lilikelykely to come in contact with water).They start discharging larvae 1100 to 14 months afteafterr infection Diagnosis -intense itching and burning pain at the site of the blister which is a characteristic of the disease presence of actively moving larvae when blister burstsbursts

ORDER: SPIRURIDA FAMILY:FILARIOIDAE DISEASE:

WUCHERARIA BANCROFTI DiseaseElephantiasis Morphology Adult is long, threadlike, creamy white worm. FemalePosterior end is finely tuberculated, Male tail end is curled ventrally, contains 2 spicules of unequal length. Males and females remain coiled together. Lifecycle The adult live in the lymph glands and ducts where they form tight coils. The females which are ovoviviparous produce thousands of prelarval stages called microfilariae which are ensheathed in the egg membrane. These microfilariae pass into the blood stream through the thoracic duct. The microfilariae also exhibit nocturnal periodicity in the peripheral blood. They accumulate in the peripheral circulation around midnight (btw 11pm and 2am), but remain in the deep circulation particularly vessels of the lungs during the daytime. The intermediate hosts (vectors) are various species of mosquitoes(Culex, Aedes, Anopheles and Mansonia)female.When a mosquito bites man, it sucks blood containing microfilariae which lose their sheath in the stomach and migrate to the thoracic muscles within few hrs. They undergo the 1 st moult and become the 2 nd stage larvae which is the characteristic sausage shape Diagram

About 2 wks after, the 2 nd moult occurs producing the 3 rd stage (filariform) larva which is the infective stage. The larvae migrate to the proboscis sheath and when the mosquito bites man, the larvae escape into the skin and gain entrance into the body through the bite wound. They migrate through the lymphatic system, finally settling in their definitive site where they become sexually mature in about 9 months. Diagnosis Demonstration of microfilariaein stained thick blood film and unstained film Demonstration of adult wormsin biopsy sample

Loa loa (Eye worm) Disease: Loiasis Found in the subcutaneous tissues of man, periodically crossing the eyeball under the conjunctiva and cornea (hence the name eye worm). The migration induces allergic responses resulting in the formation of cutaneous swellings known as “calabar swellings”. Morphology Presence of a small wartlike bosses covering the cuticle is characteristics. Males2034mm long by 350430m in diameter Female2070mm long and 425 m in diameter. Microfilariae are sheathed measuring 250300m in length. Lifecycle Similar to that of W.bancrofti. The microfilariae also show periodicity, but this time diurnal, accumulating in the peripheral blood in the day and concentrating in the lungs at night. This appears to be an adaptation to the biting habits of the insect vectors which are certain species of the mangrove or deer fly ChrysopsC.silacea, C.climidiata which are daytime biters. Mansonia africana however has been suggested to be important vector iinn Nigeria (Ogunba, 1977) Development of larvae in the vectors follow the same pattern as in W.bancrofti , but the 3 rd stage (filariform) larvae develop in the fat body ooff the fly before migratingmmigrigratingating to the mouth parts. Man becomes infected when the fly transmits larvae during feeding (bites man fforor blood meal). Life span in man is appr ox 15yrs. Diagnosis Clinical presence of calabar swellings presence of an adult worm crossing the conjunctiva Demonstration of microfilariae in the blood

ONCHOCERCA VOLVULUS Disease: causes blindness (river blindness) Morphology Adult worms are whitish, opalescent with transverse striastriatestes on the cuticle. Posterior end is coiled thus the name onchocerca.(curledonchocerca.(curled tail). Male 16 to 42mmx0.12 0.2mm, female2350cmx0.30.5mm. Adult worms are coiled together in the subcutaneoussubcutaneous tissue. Lifecycle In 2 hosts. Mandefinitive host, intermediate host blackflies of the genus Simulium. The nodules containing the adults are usually located aabovebove the waist in central AmericAmerica,a, below the waist in Africa. This is due to the adaptation of the differences in the biting habits of the respective insect vectors (various species of the bblackflieslackflies simulsimulium).ium). Their mouth parts are modified for feeding on tissue juices of animals anandd man from just under the epidermis. Thus when they bite an infected man, they inge st microfilariae along with the tissue juices. The development in the fly follows the same pattern as in other filariae. TThehe 1 st stage larva migrates to the thoracic musculature where it moultmoultss to form the sasausageusage shape. This moults into the 3 rd larva whi ch is the filariform, then position itself around thethe labium from where it gains entry into a new host when the insect feeds. They embark on a route (not(not clear) to their definite locationsubcutaneous tissue.Lifespan of adult is approx 16yrs,16yrs, microfilariae 30 months in the skin. Diagnosis examining biopsy material of the subcutaneous nodulesnodules for adult worms also examining skinsnip biopsies under the microscope for microfilariaemicrofilariae microfilaria can also be found in urine, sputum, bloodblood or lymph.

PHYLUM ARTHROPODA Classification

SOME PARASITIC ARTHROPODS 1. Sub Phylum Chelicerata Class:Arachnida Order: Acarina(Ticks and Mites)

TICKS Suborder—Ixodides Family 1(soft ticks)Argasidae Family 2(hard ticks)Ixodidae Family-Argadidae ExampleOrnithodoros moubata Lifecycle The adult hide in dust and crevices of huts in Africa. The tick is nocturnal and feeds on blood of host which include man, rabbit, goat, pig etc. Eggs are deposited in batches of 35 to 340 eggs by impregnated female. This is done between meals from any of the hosts. A non motile larva forms within each egg 7 to 11 days after eggs are oviposited. Few hrs after, the larva undergoes the 1 st moult and transforms into the 1 st nymphal stage. The nymph escapes from the shell and attaches itself to a passing host and remains there for 5 to 7 days feeding on the host’s lymph. At the end of which the nymph drops from the host and undergoes the 2 nd ecdysis2nd nymphal stage. 6 to 9 of such feeding periods take place each one followed by a molt before the nymph reaches the adult stage. In the transmission of relapsing fever spirochaete, The cycle involves mantoman not animaltoman feeding MITES Most are freeliving but some are ectoparasites on animals and some plants. Some species serve as vectors for microorganisms. Three groups based on methods used by mites to make contact with their hosts include: 1. The feather fur and mange mite. Found on gregarious birds and mammals. Spend their entire life span on their hosts. 2. The nest mite(Nidicoles)parasitize nest and burrowdwelling . Only found on their host during the feeding period only. Feed less frequently, but the amount of blood taken at feeding period is great. 3. Larval mites or Chiggers: Attach to their host only while feeding , however feed less frequently than the Nidicoles. Are not host specific. Can feed on any host. They are thus the group of most importance in disease transmission.e.g. Larval Thrombiculidae or chiggers.

SUBPHYLUM CRUSTACEA Some parasitic Crustaceans Class Maxillopoda Subclass Copepoda Subclass Branchiura Subclass Subclasss Cirripeda

Subclass Copepoda- are small elongate, tapering towards the posterior end

Lifecycle of copepods. Eggs hatch into active larva called the nauplus larvae. Among the parasitic species, the nauplus larvae moult 4 times. As one nauplus stage molts and metamorphosis into the subsequent stage, the body elongates and the number of appendages increases. Active feeding occurs in between ecdysis. After feeding, the last nauplus generation which possesses the full appendages undergoes another molt and is transferred into an adult. Example of parasitic copepod These include Order Cyclopoida e.g. Bomolochus species. This is parasitic in fishes and in a few invertebrate.

CLASS:INSECTA GENERAL CHARACTERISTCS SOME PARASITIC INSECTS ORDER SIPHONAPTERAThe Fleas ORDER MALLOPHAGAThe biting lice ORDER ANOPLURAThe sucking lice ORDER DIPTERAThe Flies, mosquitoes ORDER HEMOPTERAThe true bugs 1. ORDER SIPHONAPTERA-The fleas Lifecycle Eggs are oviposited either on or off the host. Metamorphosis is holometabolic. Hatching is influenced by environmental temperature and humidity. Larvae undergo 2 molts to give rise to the pupa. Pupae remain within the cocoon for 7 days to as long as a year depending on condition. The form ruptures to give the adult which is parasitic. ExamplesTunga penetrans (sand flea),

ORDER ANOPLURA (Sucking Lice) . Are Hemimetabolous, the life stages being the egg, nymph, and adult. All adults are wingless. Sucking lice are parasitic on mammals but never attack birds.

Disease transmits include relapsing fever (Spirochaete).

ORDER MALLOPHAGAThe Biting or chewing lice Lifecycle Are hemimetabolous. Entire cycle occurs on the host.. This undergo 3 nymphal stages

ORDER DIPTERAThe Flies, mosquitoes

SANDFLY- Genus Phlebotomus . A genus of biting flies, called sandflies, the females of which are bloodsucking. They are vectors of various human diseases, including kalaazar , Carrion's disease, cutaneous leishmaniasis and or sandfly fever . Life cycle Are Holometabolous.Females lay eggs in batches in cracks and crevices

Hatching occurs into the larval stage. The larvae metamorphose into pupa and then adult.

Common name: Black flies scientific name: Simulium spp.

Life Cycle and Description . Females deposit eggs, 200 to 800 per female, on vegetation just below the water surface. Are also Holometabolous.Larvae emerge from eggs and attach themselves to aquatic or emergent vegetation as well as rocks. by. Larvae pass through six stages before reaching the pupal stage. Pupae are encased in a silken cocoon attached to vegetation or other objects in the stream. Adults emerge from the pupal case through a slit and float to the surface on a bubble of air. Some species mate as soon as adults emerge. The length of the cycle from egg to adult is variable, depending on the black fly species and water temperature.

Mosquito

Mosquitoes are holometabolous insects and all larval stages are aquatic. The females of most species have piercing and sucking mouth parts and apparently they must feed at least once upon mammalian blood before their eggs can develop properly. The males may have beaks, or probosces, but cannot pierce, and they feed upon fruit and plant juices.

LIFECYCLE Mosquitoes go through four stages in their life cycle: egg , larva , pupa , and adult or imago . Adult females lay their eggs in water, which can be a saltmarsh, a lake, a puddle, a natural reservoir on a plant, or an artificial water container such as a plastic bucket. The first three stages are aquatic and last 5–14 days, depending on the species and the ambient temperature; eggs hatch to become larvae , then pupae . The adult mosquito emerges from the pupa as it floats at the water surface. Adult females can live up to a month – more in captivity – but most probably do not live more than 1–2 weeks in nature.

Disease

The principal mosquito borne diseases are the viral diseases yellow fever , dengue fever and Chikungunya , transmitted mostly by the Aedes mosquitoes , and malaria carried by the genus Anopheles .

Genus: Chrysops Life cycle: The female oviposits on objects such as leaves, stems and logs overhanging on streams and ponds. Eggs are laid in masses and glued to these objects. The eggs hatch into larvae,which burrow into loose soil where the pupae are formed. The pupae are stationary. Adults are formed from the pupae. Adults are strong fliers and will travel long distances for food. The female requires a blood meal to develop its eggs. They are mostly day bitters though a few feed at night. Medical Importance: C.silicae and C.dimidiata (found in Nigeria) are involved in the transmission of Loa loa a filarial worm, .

Genus: Glossina (tsetse flies) Life cycle: Glossina species do not lay eggs instead one egg develops and hatches in uterus where the larva is nourished by milk glands until it matures. The adult female lays the larvae in a warm soil under fallen trees or sheltered places where it develops further .The developed larva burrows into the soil and change to pupa and after about 15 to 30 days, the adult fly emerges and pushes its way out of the loose soil. The flies feed on blood (both male and female). Both also are capable of transmitting diseases to man. Medical Importance: Main medical importance is the transmission of T rypanosome that causes Trypanosomiasis,.