SCHISTOSOMIASIS IN LAKE MALAWI

Background In 1992 two US Peace Corps volunteers (PCVs) developed cent ral nervous system schistosomiasis due to infection with Schistosoma h aematobium following recreational water exposure at Cape Maclear on La ke Malawi, an African lake considered by many to be free of schistosom iasis, To determine the transmission potential and risk for aquiring s chistosomiasis in Lake Malawi, a cross-sectional survey of resident ex patriates and visitors to Malawi was done during March and April, 1993 . Methods A volunteer cohort of expatriates and visitors representing a cross-section of Malawi's foriegn population answered detailed quest ions about freshwater contact and provided blood specimens to determin e the seroprevalence of S haematobium and S mansoni by ELISA and immun oblot analyses, A survey for Vector snails was conducted along Lake Ma lawi's southwestern shore. Findings The study population of 955 includ ed 305 US citizens and 650 non-US foreign nationals. 303 of the study population had seroiogical evidence of current or past schistosome inf ection. Seroprevalence was 32% (141/440) among expatriates whose fresh water exposure was limited to Lake Malawi; S haematobium antibodies we re found in 135 of 141 (96%) seropositive specimens. Risk of seroposit ivity increased with the number of freshwater exposures at Lake Malawi resorts. Although many resort areas in the southwestern lake region p osed a significant risk, Cape Maclear was the location most strongly a ssociated with seropositivity (OR 2.9, 95% CI 1.6-5.1). Methods Schist osome-infected Bulinus globosus, the snail vector of Objectives S haem atobium in Malawi. were found at Cape Maclear and other locations alon g the lakeshore. Interpretation S haematobium infection is highly prev alent among expatriates and tourists in Malawi, Recreational water con tact at popular resorts on Lake Malawi is the most likely source of in fection. Transmission of schistosomiasis is occurring in Lake Malawi, a previously under-recognised site of transmission.