It’s a Fluke!

Schistosomiasis, aka bilharziasis, is caused by infection with parasitic trematodes (flukes) that colonize the venous system. Approx. six species cause human disease and each has its own specific geographic distribution. Each species also causes a specific clinical syndrome depending on the preferred anatomic distribution in humans of the adult worm. Schistosomal parasites of other animals may also transiently infect humans, but these lead to a dermatitis and do not live in humans.

Infection is acquired when humans enter freshwater that contain infected snails (the intermediate host). Clinical manifestations range from cercarial dermatitis (a maculopapular eruption due to cercariae migrating through the epidermis) to acute schistosomiasis (aka Katayama fever, consisting of fever, HSM, generalized adenopathy, and eosinophilia) to chronic schistosomiasis (due to adult worms in the venules of particular organs).

Clinical symptoms due to chronic schistosomiasis can occur months to years after initial infection. For S. haematobium, the main symptoms are dysuria, frequency, and hematuria. Obstructive uropathy may also develop. There also is an association between S. haematobium and squamous cell carcinoma of the bladder. For species infecting the intestines, two syndromes may develop. The more frequent and milder is of crampy abdominal pain and diarrhea, which may contain blood. Less commonly, hepato-splenomegaly, portal hypertension, and hematemesis may develop.

Management includes identifying the parasite eggs in urine or feces. Rectal snips, bladder or liver biopsies may also be employed. Serologic tests are available but are sensitive but not specific for active infection. Treatment has been greatly advanced by the development of the drug Praziquantel. The only prophylactic treatment available is avoidance of freshwater in endemic areas.