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Clonorchiasis And Schistosomiasis : Morphology, Clinical Features, Diagnosis And Treatment

Updated on April 1, 2014

The Main Vector Of The Chinese Liver Fluke Is The Fish

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Clonorchiasis (Chinese Liver Fluke Disease)

Infection of the biliary passages by Clonorchis sinensis causes clonorchiasis. This disease is prevalent, the Far East among fish eating mammals such as dogs, cats, pigs and man. It has been reported among Chinese immigrants in places like India for instance.

Morphology, lifecycle and pathogenesis: This fluke is 11 to 20 X 3 to 4 mm in size. Eggs measure 30 to 16 um and are passed in stools. The snails vectors belong to the genus Bulinus and Parafossarulus. The cercaria are ingested by fresh water fishes (more than 40 species) which form the second intermediate hosts. Metacercariae develop in their muscles. When such fishes are ingested uncooked, the cysts wall is digested and the larvae are set free in the duodenum. They pass up through the ampulla of Vater to the smaller biliary passages and sometimes the pancreatic ducts. In course of time, the biliary cirrhosis, suppurative cholangitis and rarely malignancy may occur as complications. Clinical features include diarrhea hepatomegaly, recurrent jaundice and eosinophilia.

Diagnosis: The eggs can be demonstrated in the feces or duodenal aspirate.

Treatment: Chloroquine base in a dose of 600mg daily for six weeks is effective. Praziquantel in a dose of 25 mg/Kg for one or two days is claimed to be successful.

Tortuous Varicosities in Chronic Schistosomiasis

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Schistosomiasis (Billharziasis)

Infection by Schistosoma hematobium, S. mansoni or S. japonicum constitutes Schistomiasis. Schistoma hematobium affects the urinary tract, S. mansoni affects the large intestine, liver and lungs and S. japonicum affects mainly the small intestine and upper part of large intestine, but the liver, lungs and the central nervous system are also affected frequently. S. hematobium and S. mansoni parasitize only man whereas S. japonicum may also affect other animals such as the dog, cat, rat, field mouse and cattle.

Morphology and lifecycle: The lifecycle of all the species is similar. Definitive host is man. Eggs are discharged in urine or feces. The eggs hatch out immediately in water and liberate free swimming mircidia which penetrate specific snail hosts within 24 hours (genus Bulinus for S. hematobium, Biomphalaria for S. mansoni and Oncomelanla for S. japonicum). Two sporocyst generations develop within the snail. Cercariae are formed within 4 to 6 weeks. These escape from the snail into water and remain infective for 2 to 3 days. The cercariae penetrate intact human skin and the oral mucous membrane when there is a thin film of water. Infection is acquired by contact with fresh water containing the cercariae. After entry, the cercariae lose their tails and theyr each the peripheral venules and lymphatics. Within 24 hours, they pass through the lungs, diaphragm and liver. Then they enter the systemic circulation. The parasites finally reach the portal venous system and develop into adult worms. The adult worms measure 1 to 2 cm in length and have a lifespan of 4 to 30 years. The male is broader and holds the female within its fold. The female is longer and more slender and cylindrical than the male. Within 4 to 6 weeks of infection they reach their destination through the venules draining the pelvic viscera and start laying eggs. Schistosoma japonicum passes through the superior mesenteric vein and S. mansoni passes through the inferior mesenteric veins. Finally, they both reach the submucosal vessels of the intestine. Schistosoma japonicum affects the small intestine and the ascending colon, while S. mansoni lodges in the descending colon and rectum. Schistosoma hematobium reaches the bladder and other pelvic organs.

The females lay about 3000 eggs daily in the terminal blood vessels. The worms slowly retreat as the terminal vessels get progressively blocked. The eggs remain viable for 3 weeks. The eggs of S. hematoblium containing miracidia appear in urine. The eggs of S. mansoni and S. japonicum are passed in feces.

© 2014 Funom Theophilus Makama

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