schistosomes lecture.pptx clinical parasitology

Schistosomes definition, life cycle, pathogenicity, treatment

1. Schistosomes Causing schistosomiasis

2. 3 main species : S. Hematobium . S. Mansoni . S. Japonicum . 2 geographically localized : S. Mekongy . S. Intercalatum .

3. General characters Unisexual ( diecious ). Males are shorter and stouter than females. Gynecophoric canal in males. Suckers anterior and ventral. Eggs are non- operculated ,with spines, and fully embryonated . Adult worms reside in venous plexuses in body of the host.

4. Life cycle Adult worms of japonicum inhabit the mesenteric veins draining iliocaecal region. Adult worms of mansoni inhabit the mesenteric veins draining sigmoido -rectal regions. Adult worms of hematobium inhabit veins of vesical and pelvic plexuses. Eggs discharged in urine ( hematobium ) and faeces. Cercariae are the infective form.

5. Pathogenicity Mainly by egg deposition in various tissues. Host immune response to antigens excreted from embryonated eggs result in granuloma formation . Cercariae may induce dermatitis within 24 hrs of invasion. (swimmer’s itch). Migration of schistosomulae into lungs provoke cough and fever. Acute schistosomiasis or katayama fever occurs after a month of infection by japonicum and mansoni . Characterised by high fever, hepatosplenomegaly, lymphadenopathy, eosinophilia and dysentery.

6. Egg passage result in bloody diarrhoea . Ulcers in the bladder causes hematuria . Burning micturition. Thickening of bladder wall. UTI , hydronephrosis , calculai , squamous cell carcinoma of bladder, cor pulmonale are complications of S. Hematobium .

7. Hepatosplenic schistosomiasis Hepatosplenomegaly due to chronic phase of S.japonicum and mansoni . Eggs deposition lead to portal hypertension due to periportal fibrosis. Splenomegaly, Ascites and finally liver cirrhosis. Diltation of abdominal collateral veins and oesophageal varices.

8. Laboratory diagnosis … . ection of characteristic ova in stool or urine. Biopsy. Filtration methods provides quantitative data. Kato-Katz thick smear –stool concentration. Antibody detection: IFAT, ELISA , RIA... Antigen detection by ELISA. Imaging : Xray , US...

9. Treatment Praziquantel is the drug of choice. Metriphonate , Oxamniquine . Hatching test for follow up.

10. Prevention Prevention of water pollution by human excreta. Eradication of the molluscan hosts in endemic areas. Avoidance of infected water. Effective treatment of infected persons.