Trematode （吸虫）

1. Trematode （吸虫）

2. Introduction • Taxonomic position • Phylum platyhelminthes • ClassTrematoda • OrderDigenea

3. Trematodes that have medical importance

4. General features • Leaf-like flattened bodies with no body cavity; with oral and ventral suckers to aid attachment to their hosts

5. The tegument is a syncytial layer equipped with spines and muscles Digestive system degenerated，with a mouth, enclosed by the oral sucker but no anus. mouth→pharynx →esophagus → two digestive tracts Hermaphrodite or monoecious except blood flukes (dimorphism) , possessing both male and female reproductive organs, the appearance and position of which are very important taxonomically General features

6. Reproductive system of trematode Female: ovary, oviduct, ootype, Mehlis’ gland, seminal receptacle, Laurer’s canal, vitellaria, vitelline duct, & uterus Male: testis, vas efferens, seminal vesicale, cirrus,&cirrus pouch

7. Life cycle is complicated – indirect life cycle Usually need one or two intermediate host – bio-helmiths The first intermediate hosts are usually fresh water snails General features

8. Eggs can only develop (hatch) in the fresh water Asexual phase: Eggsmiracidium in watersporocyst in snail redia cercaria release in water encysted metacercaria in second intermediate host – infective stage Sexual phase Preadult (Juvenile)migrated to favorable residing site  adult worm  lay eggs General features egg miracidium sporocyst redia cercaria metacercaria

9. Encysted metacercaria is usually the infective stage (Schistosoma-- cercaria) Egg has operculum except blood fluke Features reflecting adaptation to parasitism Organs of attachment developed Retardation of digestive system Highly developed reproductive system General features

10. Clonorchis sinensis 华支睾吸虫(liver fluke,肝吸虫)

11. Introduction • found from the biliary passage of a Chinese in Calcutta, India in 1874 firstly. • Clonorchis sinensis is known as the oriental or Chinese liver fluke because it is distributed throughout Japan, Korea, China and Vietnam • It is estimated that there are more than 30,000,000 humans getting infection in these areas

12. It is a food-borne pathogen, causes clonorchiasis • The parasite also infects a number of other animals, including dogs, cats, pigs, and rodents, and these animals serve as reservoirs of infection --- zoonosis

13. Morphology • Adult: 1- 2.5 cm, flat, size and shape like the seed of sunflower • With oral sucker and ventral sucker • The two testes of the male productive organ are branched

14. Sucker & spine Younger worm

15. pharynx oral sucker vitellaria digestive tract ventralsucker uterus Seminal receptacle ovary Excretory bladder Testis ceca

16. Eggs • Average 29×17µm, yellow brown • The smallest helminth egg • Light bulb shape which also looks like sesame or water melon seeds • Operculum with distinctive shoulders • Spine or knob on posterior end • Contains miracidium when discharged

17. operculum • shoulders • spine/knob • well-developed miracidium

18. cercaria metacercaria

19. Life cycle

20. Need two intermediate hosts 1st intermediate host: fresh water snails, miracidium developed to cercaria in intestine 2nd intermediate host: fresh water fishes or shrimps, cercaria to metacercaria in muscles Infective stage: metacercaria Infective route: oral consumption of infective stage Definitive host: human being Reservoir host: dogs, cats -- zoonosis Lodging site: hepatic bile duct Life cycle

21. 1st intermediate host: fresh water snails • Parafossarulus striatulus • Alocinma longicornis • Bithynia fuchsianus

22. 2nd intermediate host: fresh water fishes and shrimps • Minnows or carps Pseudorasbora parva

23. Pathogenesis • Stage responsible for the pathogenesis: adult worm • Mechanical irritation – suckers • Toxic effects – excretions, secretions, metabolites • Biological interference – nutrition deprivation

24. Pathogenesis • Invasion of biliary epithelium inflammation  cell infiltration and proliferation  thickening of the duct wall  occlusion  extensive involvement  fibrosis of the liver  hepatocirrhosis

25. Adult worm in hepatic bile duct

26. rabbit infected with Clonorchis sinensis shows fibrosis of the bile duct

27. rabbit infected with Clonorchis sinensis shows hepatocirrhosis

28. hepatocirrhosis

29. Clinical features • Asymptomatic to heavy bile duct diseases • Hepatomegaly, jaundice, pancreatitis, bile duct stones, biliary cancer • Maximum worm burden report >70,000 worms • In child, symptoms are usually more serious, could also show malnutrition, nanoid, anemia and sometimes causes death

30. Clonorchiasis patients Clinical features Enlargement of liver and spleen

31. Clonorchiasis patients Clinical features Hepatocirrhosis with ascites nanoid kid

32. Diagnosis • History of eating raw fish or shrimps • Etiological exams • Kato-Katz method • Sedimentation method is the choice for fecal or duodenal aspiration examination if egg burden is low • Immunological diagnosis • ELISA for specific antibodies or circulating antigens

33. Epidemiology and control • Distributed in the Far East including China, Korea, Japan, Vietnam and far east part of Russia • In china, it covers 25 provinces with the highest prevalence in Guangdong (5,000,000 cases), totally 10,000,000 reported cases over the country in year 2003 survey • Dietary habit is the hard part for the disease control

34. Factors associated with endemic: Existence patients and reservoir hosts (cats & dogs) Presence of first & second intermediate hosts in the same water body Mode of fish breeding Dining habit and custom Epidemiology and control

36. Control measurements: Hygiene education – avoid eating raw or undercooked freshwater fishes; separate the raw and cooked food preparation area Protect fish pond from being contaminated by the feces Control of reservoir hosts – pets at home, no raw fresh-water fish for cats Cure patients and carriers – Praziquantel (drug of first choice),25mg/kg，tid×3d Epidemiology and control