Trematodes By Godwin E Ibe ML 609 Class

Trematodes By Godwin E. Ibe ML 609

Class Trematoda z. There about 9000 species of trematodes all of which are parasitic. Most parasitize vertebrates. z. Adaptations for parasitism include suckers and hooks for attachment, glands to produce cyst material and increased reproductive capacity.

Sheep liver fluke

Class Trematoda z. Structurally, trematodes are similar to turbellarians having a well developed digestive system and similar nervous, excretory, and reproductive systems. However, a major difference is the tegument.

Tegument z The tegument (found in all parasitic Platyhelminthes) is a nonciliated, cytoplasmic syncytium that overlays layers of muscle. z The syncytium represents extensions of cells that are located below the muscle in the parenchyma. z The tegument protects the parasite against its host (e. g. against digestive enzymes).

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Types of Trematodes z. There are three subclasses of Trematodes, but two are small, poorly studied groups. z. The third group, the Digenea, however is a large group of major medical and economic importance.

Flat worms, a rough classification Platyhelminthes Trematoda Planaria Aspidobothrea Digenea Monogenea Cestoda

Pretty planaria, not all flatworms are ugly parasites

Flat worms, a rough classification Platyhelminthes Trematoda Planaria Aspidobothrea Digenea Monogenea Cestoda

trematodes or flukes - when they say ‘flat’ worms they mean it z All digenea are parasitic z Small dorso-ventrally flattened worms with simple anatomy and without segmentation z No coelom (secondary body cavity lined by mesoderm), but animals are filled with mesodermal parenchyma z No blood vessels, simple ladder nervous system

trematodes or flukes know your worm z Digenea posses two suckers (oral and ventral acetabulum) which they use to attach within the host z Oral sucker contains the mouth z Muscular pharynx permits the worm to pump food into the blind ending gut z Most trematodes are hermaphrodites (they are male and female, and cross as well as selffertilization occurs)

trematodes or flukes know your worm z The gut of trematodes is blind ending but can be quite extensive and highly branched (here shown in living Fasciola (liver) flukes, the dark staining is due to bile) z Smooth muscle fibers (longitudinal and cross) run under the tegument and around all the organs (the gut is shown in this picture)

trematodes or flukes know your worm z The gut is not the only organ these worms use for food uptake z The tegument (“skin”) is highly active in nutrient uptake z The epidermis is essentially a single cell (a syncytium formed by fusion of multiple cells) z The tegument’s cell bodies and nuclei underlie the two muscle layers z Actin spines are found in many species and help the worms to anchor themselves

trematodes or flukes know your worm z Platyhelminths have a simple protonephridial excretion (kidney) system z A protonephridium consists of flame cell and tubule cell z Both cells interdigitate forming a micro filter and cilia beating within this cage act as the mechanical pump z Excretes are collected from protonephridia through small ducts which merge to a central duct which opens into the excretion porus (usually towards the end of the animal) There is a nice little animation of this process a http: //www. biology. ualberta. ca/facilities/multimedia/uploads/zoology/Excretion. swf

trematodes are massively fertile – but their love life is complex z To enhance the chances to complete the complex life cycle trematodes produce massive number of offspring z The adults are hermaphrodites z The reproductive systems takes up a large portion of the body of the animal z In particular the female system is complex and different physiological functions are distributed onto different organs

trematodes or flukes know your worm z Trematodes form complex ectolecithal “eggs” z Oocytes (developing in the ovary) meet with vitelline or yolk cells (from the vitelary, which carry the bulk of the nutrients for the embryo) in the ootype which is surrounded by the Mehlis gland z An egg shell forms from secretions of the vitelline cells (the contribution of the gland to the shell is unclear)

trematodes or flukes know your worm z Worm eggs travel through the uterus to the genital pore (tens of thousands a day) z On this way the proteinacous egg shell is hardened by quinone tanning z The amino acid tyrosine is modified into a highly reactive quinone in several enzymatic steps z The quinone then cross links free amino groups of adjacent proteins generating a very stable shell z The tanning process can be visualized by following the progressive darkening of the egg shells along the uterus

Trematode life cycles z Trematodes produce an enormous number of offspring by combining sexual and asexual reproduction cycles z Asexual reproduction occurs in germinal balls. These areas are home to omnipotent (stem celllike) progentior cells that can initiate the development of embryos without fertilization z All have at least two hosts of which one is a snail z Not all stages are found in the life cycle of all species z Miracidia and cercariae are infective (invasive) stages

Trematode life cycles -the egg z The egg contains an embryo rather than an oocyte z Eggs are shed at different degrees of maturity by different flukes z Eggs have to leave the body of the final host to continue development z The mature miracidium within the egg uses light, osmolarity and temperature as clues to when hatching is appropriate z Hatching proceeds in most species through a preformed “door” the operculum

Trematode life cycles -the miracidium z The miracidium is highly motile due to the cilia on its surface z Miracidia have simple eyes (they avoid light) and several chemical and mechanical receptors which they use to find the intermediate snail host z Penetration glands secrete proteases and other lytic enzymes on contact with appropriate host z Miracidia of flukes with land snails as intermediate host will hatch upon ingestion by the snail and penetrate the gut epithelium

Trematode life cycles -the miracidium Dept. Biology, Univ. of Alberta, Canada

Trematode life cycles -the sporocyst z After penetration the miracidum undergoes metamorphosis into the sporocysts z This stage has most organ systems reduced to the bare minimum and acts as a germinal sac z The sporocyst takes up nutrients only over its tegument and the germinal mass expands and develops into daughter sporocysts, redia or cercaria

Trematode life cycles -the redia z Sporocyst can produce cercaria or a next amplification generation the redia z Redia have features of the adult fluke like oral and ventral sucker, a gut and “birth pore” to release cercaria z Redia are mobile in the snail and can prey on sporocysts and redia of the same or other species (competition)

Trematode life cycles -the cercaria z Cercaria are the stages that leave the intermediate host and infect the final host z There can be many consecutive waves of “shedding” from the snail z Cercaria already show many anatomical features of the adult fluke

Trematode life cycles -the cercaria z Reflecting the ecology of their hosts cercaria have developed an array of adaptations to achieve successful infection z Direct penetration of host skin upon water contact (Schistosoma), z Encystation within the muscle of intermediate hosts (e. g. metacercaria in fish. Clonorchis) z Encystation on plants (Fasciola)

Trematode life cycles -enhance transmission z Dicrocoelium dendriticum the lancet fluke z One metacercaria becomes the ‘brain worm’ and lodges into the central ganglia of the end z The brain worm manipulates the behavior of the ant. In the evening when the temperature drops they experience spasms of their manidibles

Trematode life cycles -enhance transmission z Leucochloridium sp. is a tiny digenic trematode living in the gut of small song birds z Worm eggs are passed with the feces and are taken up by amber snails. z Miracidia hatch, penetrate the gut epithelium and develop into sporocysts within the hepatopankreas. z Within the sporocyst cercaria develop which infect birds that eat infected snails.

Trematode life cycles -enhance transmission Amber snails (uninfected, upper panel and infected, lower panel) and Leucochloridium sp. sporocyst dissected from a snail (lower right)

Trematode life cycles -enhance transmission Dr. Oldrich Nedved, Univ. South Bohemia

Monogenean Trematodes n n n Monogeneans possess the simplest life cycle among the parasitic platyhelminths. They have no intermediate hosts and are ectoparasitic on fish (seldom in the urinary bladder and rectum of cold-blooded vertebrates). Although they are hermaphrodites, the male reproductive system becomes functional before the female part. The eggs hatch releasing a heavily ciliated larval stage known as an oncomiracidium. The oncomiracidium has numerous posterior hooks and is generally the life stage responsible for transmission from host to host. No known monogeneans infect birds, but one (Oculotrema hippopotami) infects mammals, parasitizing the eye of the hippopotamus.

Aspidogastrea Trematodes n n n Their life cycle is much simpler than that of digenean trematodes, including a mollusc and a facultative or compulsory vertebrate host. There are no multiplicative larval stages in the mollusc host, as known from all digeneans. Host specificity of most aspidogastreans is very low, i. e. , a single species of aspidogastrean can infect a wide range of host species, whereas a typical digenean trematode is restricted to few species (at least of molluscs). For example, Aspidogaster conchicola infects many species of freshwater bivalves belonging to several families, as well as snails, many species of freshwater fishes of several families, and freshwater tortoises. Trachinotus blochi (Teleostei, Carangidae), on the Great Barrier Reef. They produce large numbers of eggs which are shed in the faeces. If eaten by various prosobranch snails, larvae hatch in the stomach, and—depending on the species of snail—stay there or migrate to the digestive gland where they grow up to the preadult stage which has all the characteristics of the adult including a testis and ovary.

Digenean Trematodes n n The flukes have a complex life cycle in which a snail is the first (or intermediate) host and a vertebrate the final (or definitive host). The definitive host is one in which the fluke reproduces sexually.

Digenean Trematodes n n In some species there may be 2 or 3 intermediate hosts before the definitive host is reached. Trematodes inhabit a variety of sites in their hosts including the digestive tract, respiratory tract, circulatory system, urinary tract, and reproductive tract.

Digenean Trematodes n Digenean life cycles are very complex and the fluke passes through numerous stages.

Digenean Trematodes n A typical example would include the following stages: Adult n Egg (or shelled embryo) shed into water n Miracidium: a free swimming, ciliated larva that finds and penetrates a snail intermediate host n

Sheep liver fluke egg (top) and miracidium (bottom). http: //cal. vet. upenn. edu/projects/paraav/images/lab 6 -227. jpg

Digenean Trematodes Sporocyst: reproduces asexually in intermediate host producing more sporocysts or another asexually reproducing stage called a redia. n Redia produce more redia or cercariae. Cercariae leave the intermediate host and swim. Then they penetrate the skin of another intermediate host or the definitive host. n

Adult Fasciola hepatica Sheep liver fluke (above) Redia (right) http: //cal. vet. upenn. edu/projects/paraav/images/lab 6 -227. jpg

Digenean Trematodes n n Cercariae that enter an intermediate host may encyst in muscle and wait to be consumed by the definitive host or may leave the intermediate host to actively search for the definitive host. Cercariae that enter the definitive host make their way to their desired home and develop into an adult fluke which reproduces sexually and produces eggs. http: //www. biology-blog. com/images/blogs/trematode-cercaria-482810. jpg

Trematodes of medical importance z. Schistosoma, blood flukes z. Clonorchis & Opistorchis, liver flukes with metacercaria in fish z. Paragonimus, lung flukes with metacercaria in crabs z. Fasciolopsis, Fasciola, Dicrocoelium, intestinal and liver flukes with metacercaria on plants

Human liver fluke disease z Caused by Clonorchis sinensis and Opistorchis felinus and viverini z All locally common in East Asia and Eurasia z ~20 million people infected

Human liver fluke disease z Clonorchis and Opistorchis are quite similar causing similar disease

Human liver fluke disease z Metacercaria are found in many fish especially various carp related species z Raw or undercooked fish dishes are a source of human infection z Fertilization of ponds with untreated night soil boost infection in fish z Cats, dogs and other carnivores can be additional hosts and reservoirs

Human liver fluke disease z Pathology depends on worm burden, generally infections are light and free of major symptoms z Heavy infections Flukes residing in the bilary ducts can chronically iritate the epithelium resulting in hyperplasia of the epithelium and fibrosis around the ducts (pipe stem fibrosis) z Blockage of bile ducts and impairment of liver function, liver swelling

Human liver fluke disease z Diagnosis occurs by microscopic demonstrations of fluke eggs in the feces (~30 x 15 mm) z Prepatency is a month z Readily treated with Praziquantel

Human lung fluke disease z Paragonimus westermanii is best known but a number of other species infect humans around the world z Several carnivores serve as reservoir z Upon eating crabs by the final host metacercariae excyst in the duodenum and penetrate the gut, penetrate the diaphragm and pleura and enter the bronchioles, mature in 12 weeks z May end up in ectopic locations like brain, skin and mesentery

Human lung fluke disease

Human lung fluke disease z Adults are encapsulated in a granuloma (often two at a time) z Cyst rupture can result in cough and increase sputum, and chest pain z Chronic high worm burden can result in chronic bronchitis and dyspnea and increasing fibrosis -symptoms can be very similar to pulmonary tuberculosis z Cerebral paragonimiasis produces headaches, fever, nausea, visual disturbances and convulsive seizures

Fasciola & Fasciolopsis z Important parasite of livestock, ocasionally infects humans z Symptoms similar to Clonorchis but Fasciola is much bigger z Fasciolopsis buski the human intestinal fluke has similar ecology z Usually asymptomatic if not heavy burden

Fasciola z Ecology of fasciolosis, ponds and creeks in direct vicinity of pasture

Schistosomiasis n n Schistosomiasis (also known as bilharzia) is an infection with blood flukes and is a major infectious diseases. More then 200 million people are infected worldwide with these flukes, which they acquire swimming or walking in water in which the intermediate snail host lives

Schistosomiasis n n Schistosome eggs enter the water when infected people urinate or defecate in or near water. Eggs hatch and the miracidium seeks out a snail. Inside the snail the parasite develops into a sprocyst and asexual reproduction takes place. Cercaria eventually are released into the water.

Schistosome life cycle.

Schistosomiasis n n When a schistosome cercaria swims it takes care to avoid UV light which can damage it, but is very sensitive to the scent of humans. When it senses molecules from human skin it swims rapidly and jerks around looking for the person. When it makes contact it releases chemicals that soften the skin and it burrows in shedding its tail at the same time.

Schistosomiasis n n The fluke searches until it finds a capillary and enters it. The capillary is only barely wide enough for the fluke and it moves along using its pair of suckers. Eventually, it reaches a larger blood vessel in which it can float until it reaches the lungs and enters an artery and eventually makes its way to the liver.

Schistosomiasis n n Once in the liver, the fluke feeds on blood and begins to mature and develops ovaries or testes depending on its sex. The fluke grows dozens of times larger in the course of a few weeks and then begins to search for a mate.

Schistosomiasis n n The fluke produces chemicals to attract members of the opposite sex. Females are slender and delicate, whereas males are much bigger and have a spiny trough or groove into which the female fits and locks in.

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Schistosomiasis n n Once paired up, the pair mature sexually and travel from the liver to a permanent home that is species-specific. In Schistosoma mansoni it is near the large intestine, in S. haemotobium it is the bladder, and in S. nasale, a blood fluke of cows, it is the nose.

Schistosomiasis n n Once established the pair remain in situ for the rest of their lives. The male consumes blood and feeds the female most of it, which she turns into eggs, which pass out of the host and can begin the life cycle again.

Schistosomiasis n n Schsitosomiasis has a low mortality rate, but it is a chronic illness that debilitates the infected person. Symptoms can include anemia, diarrhea, fever, fatigue and van result in organ damage. In children infection can result in reduced growth and mental development.

Schistosomiasis n n Schistosomiasis occurs in tropical countries worldwide. It can be treated with oral drugs, but a lot of attention has focused on developing a vaccine and on controlling the snails which are the disease reservoir.

How do flukes manipulate their hosts? n n Many parasites infect an intermediate host that needs to be eaten by the definitive host for the parasite to complete its lifecycle. There are many instances of parasites altering their intermediate host’s behavior to make it more vulnerable to a predator (the definitive host). Such behavior is widespread in flukes.

How do flukes manipulate their hosts? n In the Carpenteria Salt Marshes in southern California lives the fluke Euhaplorchis californiensis. n It has a life cycle that includes two intermediate hosts, first the California Horn Snail and then the California killifish and a final host which can be any of a variety of fish eating birds.

How do flukes manipulate their hosts? n n n The fluke leaves its definitive host as an egg in bird droppings which are eaten by the fluke’s first intermediate host, the snail. The fluke then castrates the snail (preventing it from diverting energy into eggs and away from the parasite). The fluke then reproduces asexually and sheds cercariae into the water.

How do flukes manipulate their hosts? n n The cercariae seek out the next intermediate host the killifish and latch onto the fish’s gills. Each cercaria works its way into a blood vessel and explores until it finds a nerve which it then follows until it reaches the fish’s brain.

How do flukes manipulate their hosts? n n The cercariae don’t penetrate the brain but sit on top of it. Then they wait for the fish to be eaten by a bird. Once eaten by a bird they break out of the fish’s head and move into the bird’s gut where they produce eggs that continue the cycle

How do flukes manipulate their hosts? n n The cercariae sitting on the bird’s brain apparently don’t sit passively waiting. Killifish when swimming occasionally shimmy and jerk around flashing their bellies. Those infected with cercariae are four times more likely to do so than noninfected fish.

How do flukes manipulate their hosts? n In field experiments in which penned fish were made available to foraging birds infected fish were 30 times (!) more likely to be eaten than uninfected fish.

How do flukes manipulate their hosts? n n Research on how the flukes alter the fish’s behavior has shown that the flukes produce powerful molecular signals called fibroblast growth factors. These interfere with the growth of nerves and may be the mechanism the flukes use.

Do trematode parasites favor sex in hosts? n n n Lively (1992) studied New Zealand freshwater snail. Host to parasitic trematodes. Trematodes eat host’s gonads and castrate it which imposes strong selection pressure. Snail populations contain both obligate sexually and asexually reproducing females.

Do trematode parasites favor sex in hosts? n n Proportion of sexual vs asexual females varies from population to population. Frequency of trematode infections varies also.

Do trematode parasites favor sex in hosts? n n If evolutionary arms race favors sex, then sexually reproducing snails should be commoner in populations with high rates of trematode infections. Results match predictions.

White slice indicates frequency of males and thus sexual reproduction

Frequency of males increases with increasing rates of trematode infection.

The End! Thank You!