Factors that should raise suspicion for schistosomiasis:
(1) travel to a country endemic for schistosomiasis
(2) contact with fresh water in the endemic country, especially bathing, swimming, boating, kayaking or rafting
(3) participation in an adventure trip
(4) signs and symptoms suggestive of acute schistosomiasis 3 to 8 weeks after exposure
(5) if a member of a group, the diagnosis of schistosomiasis in other members who had similar exposures
(6) longer exposures (although infection may occur after a single exposure, prevalence increases with the length of the exposure. It is very high for exposures > 7 days)
Travelers may underestimate the risk because:
(1) they may not be familiar with schistosomiasis
(2) they may think that the risk is low if certain conditions are present (fast moving river, season, etc.)
Clinical findings that may indicate acute schistosomiasis:
(1) fever
(2) cough
(3) hepatitis with elevated liver function tests
(4) eosinophilia
(5) hematemesis
(6) hematuria
(7) dysuria
(8) diarrhea
However, almost half of infected travelers may be asymptomatic, so a high index of suspicion is required to make the diagnosis.
Diagnostic tests:
(1) stools and 24 hour urine examinations for ova and parasites. Eggs will not be excreted until the initial worm has had a chance to mature, which may take up to 7 weeks after the exposure.
(2) serologic testing (indirect hemagglutination or ELISA screen, with confirmatory immunoblot testing)
(3) tissue biopsy
(4) antigen testing (if chronic and significant infection present)
The demonstration of seroconversion to positive in a tourist is highly suggestive of infection. Since the antibody may persist for years, a positive serologic test in a person who has been treated may not be an indication for retreatment; the decision to treat is based on the results of the other tests and the recent exposure history.
