Environmental Predictors of Schistosomiasis Persistent Hotspots following Mass Treatment with Praziquantel
Schistosomiasis is a parasitic disease that impairs the physical and cognitive development of more than 200 million individuals globally, as a result of physiological disruptions associated with repeated infections. Intermediate snail hosts facilitate the transmission of Schistosomiasis to human and livestock populations. Ongoing management efforts include the improvement of water quality and sanitation in tandem with mass drug administration (MDA) of praziquantel (PZQ) in areas of active transmission. Although treatment with PZQ reduces Schistosome burden, many regions, known as persistent hotspots (PHS), exhibit sustained infection-levels, despite repeated administration campaigns. As PZQ treatment does not prevent future Schistosoma infections, the absence of simultaneous environmental control efforts during periods of MDA undermines the effectiveness of these control efforts. The complexity of factors contributing to a region’s likelihood of becoming a PHS further complicate work to combat or prevent PHSs.
Using data from the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE), we modeled previously unexplored environmental contributors to PHS. We classified areas as “hotspots” or “responders” according to observed declines in the prevalence and intensity of Schistosoma infection in response to MDA trials. The model explored the relationship between classification and potential environmental factors such as proximity to freshwater, cropland cover, population density, and rainfall to determine factors contributing to PHS risk. Villages assigned hotspot status were observed to experience less frequent MDA campaigns. Additionally, many models exhibited a negative relationship between PHS risk and both proximity to freshwater as well as cropland cover. The models developed in this study can aid decision-makers in targeting the regions most at-risk for or currently experiencing persistent Schistosomiasis infection and in identifying environmental factors that disrupt treatment. This information may help limit these disruptive effects and improve the success of MDA campaigns.
Joseph W. Walker, Nupur Kittur, Sue Binder, Jennifer D. Castleman, John M. Drake, Carl H. Campbell Jr., Charles H. King and Daniel G. Colley. Am J Trop Med Hyg. 2019 Dec 30. doi: 10.4269/ajtmh.19-0658.