Medical Biology

Dr:Fadia Al-kahyat

Platyhelminthes

Class:Trematoda  Trematoda is a class within the phylum platyhelminthes. It includes two groups of parasitic flatworms, known as flukes.  -They are internal parasites of vertebrates.  -The body is non-segmented, with unpronounced head and incomplete digestive system(closed system).  -They have one or more suckers.  -They are mostly hermaphroditic with highly developed reproductive system  Trematodes have a complex life cycle with at least two hosts. The primary host, where the flukes sexually reproduce, is a vertebrate. The intermediate host, is usually a snail.

Fasciola hepatica • Fasciola hepatica, also known as the common liver fluke or sheep liver fluke, is a parasitic flatworm (a type of helminthes) of the class Trematoda, phylum platyhelminethes that infects the livers of various mammal. • Is one of the largest flukes of the world, reaching a length of 30 mm and a width of 13 mm. It is leaf-shape, pointed posteriorly, and wide anteriorly. • The oral sucker is small but powerful and is located at the end of a cone-shape projection at the anterior end(gives the worm the appearance of having shoulders). The ventral sucker ( acetabulum) is larger than the oral sucker and is anterior. • The digestive system is composed of a mouth leading to a muscular pharynx, a short esophagus bifurcating in front of the acetabulum to two intestinal Caeca on sides of the body and extending till the posterior end of the body. Each caecum is highly dendritic but with closed ends.

 Life cycle  The adult worm passes eggs out of the liver with the bile and into the intestine to be voided with feces.  Upon reaching water, egg will complete its development and hatches as miracidium which has to find its suitable intermediate host(snails of lymnaea ). Inside the snail, the miracidium change to sporocysts which produces mother rediae • Each mother rediae produces daughter rediae that develop in the snail. • -Daughter rediae produces cercariae which leave the snail and swim freely to attach to aquatic plants and change to metacercariae. • -When a mammal eats metacercariae encysted on vegetation, juvenile fluke excysts in the small intestine and immediately penetrates the intestinal wall, enters the coelom, and creeps over the viscera until contacting the capsule of the liver.Then it burrows into the liver parenchyma, feeds and grows and finally enters bile ducts.

Schistosoma spp.

• Three species infect human : • 1- S.mansoni causes the intestinal bilharzia • 2- S.haematobium causes the urinary bilharzia • 3- S.japonicum causes the Japanese or oriental bilharzia • -Schistosoma, commonly known as blood-flukes, are parasitic flatworms • infections in humans termed schistosomiasis (bilharzia or bilharziasis) .

• These parasites live in the branches of the lower and upper mesenteric veins(according to the species). • Adult worms have elongate tubular bodies. its sex separated .The males are shorter and wider than the females, length varies according to the species. • Unlike all other trematodes, schistosomes are not hermaphroditic but dioecious

Location of Schistosoma spp.

Adult worms of S. mansoni live in the veins draining the rectum and colon, and in branches of the portal vein in the liver. Adults of S. japonicum live in the anterior mesenteric blood vessels and in the portal vein in the liver. Whilst the adults of S. haematobium live in the vesicles of the bladder. Life cycle 1-Once the eggs are laid by the adult female worms the majority of them first pass through the veins of the blood vessel in which the worm is

4 living, and then into the lumen of the intestine and are passed in the faeces (S. mansoni and S. japonicum). Or into the lumen of the bladder, and are then passed in the urine (S. haematobium). 2-Those eggs that reach fresh water hatch, releasing a miracidium which, to develop further must infect a snail of the correct species within 24 hours. 3-Asexual multiplication takes place in the snail, and results in the release of cercariae (minute in size with forked tails, 200m long) into the water about 3 – 6 weeks later. 4-Cercariae actively swim around and when they have located, or come into contact with, a definitive host they actively penetrate the skin. They can stay active looking for a host for 24 – 48 hours after which if they don’t find a host they will die. 5-cercariae migrates to the liver and develops into either adult male or female worms (flukes), here they pair up and then migrate to their region of the venous blood system (species specific sites). 6- The females leave the males and moves to smaller venules closer to the lumen of the intestine or bladder to lay her eggs (about 6 weeks after infection). The majority of adult worms live from 2 – 4 years, but some can live considerably longer. Life cycle form five different developmental stages: eggs, miracidia, sporocysts, cercariae and adult worms

S.Mansoni lateral spine Schistosoma haematobium eggs elongated with a prominent terminal spine

S. japonicum ova oval in shape with a minute lateral spine or knob

Platyhelminthes-Cestoda

Cestoda :is a class of parasitic flatworms, which are commonly called tapeworms. All cestodes are parasitic, typically they live in the digestive tracts of vertebrates as adults. There are around 3,500 species described. They are usually less than 1 mm and some species up to 30 m. The larvae live in intermediate host which can be a vertebrate or invertebrate according to species. In the vertebrate gut they are surrounded by food so have no need for a mouth or gut of their own. Nutrients are absorbed directly through the surface which has many folds increasing the surface area. Cestodes body consist of a head ( attachment organ) known as a scolex that is equipped with suckers and spiny hooks with which it attaches itself to its host's intestinal wall. Behind the scolex the body is formed of segments (proglottids), the nearst proglottids to the scolex are immature which then develop to be mature and after fertilization become gravid so the oldest segments are at the posterior end. Tapeworms are hermaphroditic and the end segments are essentially just bags of eggs that have been fertilized by sperm from the same segment, a different segment of the same worm, or a different worm

Taenia saginata

Taenia saginata, commonly known as the beef tapeworm, is a zoonotic tapeworm which causing taeniasis in human and cysticercosis in cattle , the definitive hosts harbouring the adult worms are humans while the intermediate hosts are cattle where larval development occurs

T. saginata is the largest species in the genus Taenia. An adult worm is normally 4 to 10 m in length , but can become over 22 m long and can have as many as 1000 to 2000 proglottids. The body is flattened dorsoventrally. It is entirely covered by a membrane called tegument. The body is white in color and consists of three portions: scolex, neck, and strobila. The scolex has four suckers, neither hooks nor rostellum are found. The rest of the body proper(the strobila) is basically a chain of numerous body segments called proglottids. The neck is the shortest part of the body, and consists of immature proglottids. The midstrobila is made of mature proglottids that eventually lead to the gravid proglottids, which are at the posterior end. An individual T. saginata does not have a digestive system, mouth, anus. It derives nutrients from the host through its tegument, as the tegument is completely covered with absorptive hair- like microtriches. It is also an acoelomate ( having no body cavity). The inside of each mature proglottid (wider than long) is filled with muscular layers and complete male and female reproductive systems,

7 including the tubular unbranched uterus, bilobed ovary, genital pore, 300- 400 testes, and vitelline gland. In the gravid proglottid(longer than wide), the uterus contains up to 15 side branches filled with eggs. On each side of the proglottid, ventral and dorsal longitudinal excretory canal are present. At the posterior end of each proglottid, a transverse excretory canal connects the ventral longitudinal excretory canals of both side.

Life cycle

1-Adult worm found in the small intestine of humans as consider to be the only definitive hosts. Eggs or gravid proglottid will pass with feces, the eggs can survive for days to months in the environment.

2- Cattle become infected by ingesting vegetation contaminated with eggs or gravid proglottids. In the animal's intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they

8 develop into cysticerci. A cysticercus can survive for several years in the animal

3-Humans become infected by ingesting raw or undercooked infected meat . In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. The adult tapeworms attach to the small intestine by their scolex

The signs and symptoms of taeniasis

Most people with tapeworm infections have no symptoms or mild symptoms. Patients with T. saginata taeniasis often show more symptoms that those with T. solium infections because the T. saginata tapeworm is larger in size (up to 10 meters (m)) than the other tapeworm (usually 3 m). Tapeworms can cause digestive problems including abdominal pain, loss of appetite, weight loss, and upset stomach. Taenia solium

Another Taenia.sp that infected human is Taenia solium commonly known as pork tapeworm. This is similar in many respects with T.saginata , however the following comparison shows their main differences.

Nemathelminthes

• The Phylum is also known as Nematoda consists of the species commonly known as roundworms or threadworms. There are approximately 12,000 described species. • Characteristics of Nematodes • -Roundworms are small, slender, unsegmented worms which are tapered at both ends. Most nematodes have the same simple body plan. Their bodies are bilaterally symmetrical (one half is a mirror image of the other). • -Size varies from microscopic to pencil-size. • - Nematodes are characterized by an external (outer) layer of cuticle that is secreted by the hypodermis, The cuticle is somewhat rigid. However, it is flexible enough to permit bending and stretching, and can be penetrated by gases and water. • - Nematodes lack a true coelom (body cavity). Instead, they possess a fluid-filled pseudocoel (incomplete coelum) that contains the intestine and reproductive organs. In pseudocoeloms, however, the cavity is lined with mesodermal tissue on the outside but endodermal tissue internally. Endodermal tissue develops into the digestive tract, while mesodermal tissue can become a number of different body components, including bones, skin, and the liver • -Simple Digestive System, Although nematodes lack a well- defined head, they do have a mouth at one end of their bodies. The roundworm uses the 16 organs in its mouth to bring food into its digestive system. From the mouth, the food goes into the pharynx where it is crushed by muscles. The food then goes into the gut for digestion. The nutrients move to the cells and the waste moves out of the body, two excretory canals located on either side of the nematode's body. The waste eventually leaves the worm's body through its anus located at the opposite end of the cylindrical body. • -Circular nerve ring with dorsal and ventral nerve cords. • -Sexes usually separate, Male is smaller than female. • -Complete digestive system. • -Circulatory and respiratory organs are lacking. • -Excretory system consist of one or more large gland cells opening to an excretory pore or canal system.

Basic Life Cycle

There is diversity within the life cycles of different nematodes; however, all nematodes follow the same basic pattern of growth and

reproduction. The nematode life cycle has seven stages, including an egg, four larval stages and two adult stages. Sexual reproduction is generally initiated by adult female nematodes that have attached themselves to a host organism. The female lays eggs that are passed by the host to the external environment where the eggs then pass through three developmental stages before becoming larvae.

Ascaris lumbricoides (Large Roundworm of Man)

Morphology The adult Ascaris lumbricoides are large white, or pinkish-white, cylindrical roundworms, slightly narrower at the head. The more slender males measure between 10 to 30cm long and have a curved tail with two spicules, but no copulatory bursa. The females are very similar, being slightly larger at between 20 to 35cm long, a vulva approximately a third of the length of the body down from the head, and have a blunt tail. They are both characterized by having a smooth, finely striated, cuticle, and a mouth, which is characteristic by having three lips . Adult worms1live in the lumen of the small intestine. A female may produce up to 240,000 eggs per day, which are passed with the feces . 2 Fertile eggs embryonate and become infective after 18 days to several weeks , 3 depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed ,4 the larvae hatch , 5 invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs . 6 The larvae mature further in the lungs (10-14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed .7 Upon reaching the small intestine,

11 they develop into adult worms 1 . Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female.

Ancylostoma duodenale

• It is a parasitic nematode worm and commonly known as the Old World hookworm. Ancylostoma duodenale is an S-shaped worm

because of its flexure at the frontal end. Small cylindrical worm, greyish-white in color. Males are 8 mm to 11 mm long with a copulatory bursa at the posterior end. Females are 10 mm to 13 mm long, with the vulva located approximately one-third of the body length from the posterior end. females can lay 10,000 to 30,000 eggs per day. Both male and female hookworms have two powerful ventral teeth in the adult forms of the parasite, one along each side of the buccal capsule; smaller pairs of teeth are located deeper in the capsule. It lives in the small intestine of hosts such as humans, cats and dogs. • Life cycle

• 1-The egg stage: Hookworm eggs pass through the intestinal tract of an infected host and are eliminated from the body in the stool. Within two days, the eggs will hatch in warm, moist soil. The larvae will live there, waiting for a host.

• 2- The Rhabditiform Larval Stage: The first form of the larval stage is called a rhabditiform larva, which exists in contaminated feces or soil. For five to ten days, the larva will grow and molt two times.

• 3- The Filariform Stage:After molting for the last time, the larva will enter a filariform stage. The worm larva can then infect a host. Filariform larvae can survive for up to a month in the soil. If a host touches the contaminated area, the larva enters through its skin. It then moves to the circulatory system and is carried to the lungs.

• The larva will exit the lungs, entering the alveoli and traveling up the tracheal tree. The host will eventually cough up the larva and swallow it. The larva will pass through the digestive tract to the small intestine, where it will grow into an adult.

• 4- The Adult Stage:An adult hookworm will attach itself to the wall of the small intestine, feeding on the blood of the host and reproducing. Females will then lay eggs in the digestive tract to repeat the life cycle. Adult hookworms can live in the intestine for up to two years.

Enterobius vermicularis

• As a nematod , Enterobius vermicularis which cause enterobiasis, has a cylindrical body, and a cuticle with three main outer layers made of collagen and other compounds, secreted by the epidermis. The cuticle layer protects the nematode so it can invade digestive tracts of animals. The worms molt four times, the first two before hatching, and then before their adult stage. • Males are 2-5 mm long by 0.1-0.2 mm wide and have a curled tail, where females are 8-13 mm long by 0.3-0.5 mm wide with a pointed tail. This pointed, or "pin" shaped tail is how E. vermicularis received its common name: pin worms. Females are also distinguished by their alae, or wing-like, anterior expansions of the body wall. Both sexes have three lips surrounding the circular mouth. • Eggs are elongate and characteristically flattened on one side, measuring 50-60 µm by 20-30 µm. The eggs have five membranes: one inner, lipoidal layer, three middle layers known as membrana lucida, and one outer, albuminous membrane which coats the egg. This membrane makes the eggs sticky and therefore itchy to the host, which is important in the life cycle. The larvae differ from adults only in that they are smaller and coiled. • As a member of the Secernentea, Enterobius vermicularis has a specialized tubular excretory system with three canals. The canals are arranged to form an "H".