Schistosomiasis is to a degree a disease of contact with fecally contaminated surface waters, rather than ingestion. Repeated treatments with praziquantel reduce schistosomiasis prevalence and morbidity, however transmission persists and prevalence of infection often recovers within a few years.
In a community in rural Bahia, Brazil that straddles a shallow river, we surveyed and treated all individuals that tested positive for schistosomiasis by Kato Katz in stools in 2009, 2012, 2013, 2015, and 2017. Upstream and downstream, as well as common water contact sites along the river were sampled and analyzed by microbial source tracking for human fecal indicator markers. The location of each home and water contact site was registered with a hand held GPS unit. Spatial analyses were performed by using QGIS software version 2.14.
The population in the village was 460 in 2009, with minimal fluctuation over the study period. In 2009, schistosomiasis prevalence was 45%. After successive rounds of community-wide treatment with praziquantel, in the years 2012, 2013, 2015, and 2017, prevalence decreased to 24%, 16%, 13%, and 1.6%, respectively. Among the river water samples, human fecal indicator markers were detectable in minimal quantities upstream of the village. The highest concentrations were found in the downstream sections of the village. Hotspot analysis, raster calculator, and nearest neighbor analysis were used to display and analyze the prevalence of schistosomiasis. Distribution of infection was widespread initially and clustered in the downstream sections of the village after successive treatments.
In this rural community in Brazil, sustained decrease in schistosomiasis prevalence was seen after multiple community-wide treatments over 5 years. Reinfection was not distributed randomly but concentrated in the downstream portion of the village, where human fecal water contamination is increased. Targeting sanitation in key areas may decrease sources of transmission persistence after cessation of community-wide treatment efforts.
R. Ponce Terashima,
M. Reis, None