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Abstract
In 1992 two US Peace Corps volunteers (PCVs) developed central nervous system schistosomiasis
due to infection with Schistosoma haematobium following recreational water exposure
at Cape Maclear on Lake Malawi, an African lake considered by many to be free of schistosomiasis.
To determine the transmission potential and risk for aquiring schistosomiasis in Lake
Malawi, a cross-sectional survey of resident expatriates and visitors to Malawi was
done during March and April, 1993.
A volunteer cohort of expatriates and visitors representing a cross-section of Malawi's
foregn population answered detailed questions about freshwater contact and provided
blood specimens to determine the seroprevalence of S haematobium and S mansoni by
ELISA and immunoblot analyses. A survey for vector snails was conducted along Lake
Malawi's southwestern shore.
The study population of 955 included 305 US citizens and 650 non-US foreign nationals.
303 of the study population had serological evidence of current or past schistosome
infection. Seroprevalence was 32% (141/440) among expatriates whose freshwater exposure
was limited to Lake Malawi; S haematobium antibodies were found in 135 of 141 (96%)
seropositive specimens. Risk of seropositivity increased with the number of freshwater
exposures at Lake Malawi resorts. Although many resort areas in the southwestern lake
region posed a significant risk, Cape Maclear was the location most strongly associated
with seropositivity (OR 2.9, 95% Cl 1.6-5.1). Schistosome-infected Bulinus globosus,
the snail vector of S haematobium in Malawi, were found at Cape Maclear and other
locations along the lakeshore.
S haematobium infection is highly prevalent among expatriates and tourists in Malawi.
Recreational water contact at popular resorts on Lake Malawi is the most likely source
of infection. Transmission of schistosomiasis is occurring in Lake Malawi, a previously
under-recognised site of transmission.