Trematodes

1. Trematodes By Godwin E. Ibe ML 609

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

3. Sheep liver fluke

4. Class Trematoda • 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.

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

6. 8.5

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

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

10. Pretty planaria, not all flatworms are ugly parasites

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

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

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

14. trematodes or flukes - know your worm • 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) • Smooth muscle fibers (longitudinal and cross) run under the tegument and around all the organs (the gut is shown in this picture)

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

16. trematodes or flukes - know your worm • Platyhelminths have a simple protonephridial excretion (kidney) system • A protonephridium consists of flame cell and tubule cell • Both cells interdigitate forming a micro filter and cilia beating within this cage act as the mechanical pump • 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

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

18. trematodes or flukes - know your worm • Trematodes form complex ectolecithal “eggs” • 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 • An egg shell forms from secretions of the vitelline cells (the contribution of the gland to the shell is unclear)

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

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

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

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

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

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

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

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

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

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

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

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

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

32. MonogeneanTrematodes • 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-bloodedvertebrates). • 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.

33. AspidogastreaTrematodes • Their life cycle is much simpler than that of digeneantrematodes, 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 digeneantrematode is restricted to few species (at least of molluscs). For example, Aspidogasterconchicola 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. • Trachinotusblochi (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.

34. Digenean Trematodes • 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.

35. Digenean Trematodes • 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.

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

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

38. Sheep liver fluke egg (top) and miracidium (bottom). http://cal.vet.upenn.edu/projects/paraav/images/lab6-227.jpg

39. Digenean Trematodes • Sporocyst: reproduces asexually in intermediate host producing more sporocysts or another asexually reproducing stage called a redia. • 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.

40. Adult Fasciolahepatica Sheep liver fluke (above) Redia (right) http://cal.vet.upenn.edu/projects/paraav/images/lab6-227.jpg

41. Digenean Trematodes • 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

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

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

44. Human liver fluke disease • Clonorchis and Opistorchis are quite similar causing similar disease

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

46. Human liver fluke disease • Pathology depends on worm burden, generally infections are light and free of major symptoms • 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) • Blockage of bile ducts and impairment of liver function, liver swelling

47. Human liver fluke disease • Diagnosis occurs by microscopic demonstrations of fluke eggs in the feces (~30x15 mm) • Prepatency is a month • Readily treated with Praziquantel

48. Human lung fluke disease • Paragonimus westermanii is best known but a number of other species infect humans around the world • Several carnivores serve as reservoir • 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 • May end up in ectopic locations like brain, skin and mesentery

49. Human lung fluke disease

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