Mapping of Schistosomiasis and Soil-Transmitted Helminths in Namibia: The First Large-Scale Protocol to Formally Include Rapid Diagnostic Tests

Abstract

BackgroundNamibia is now ready to begin mass drug administration of praziquantel and albendazole against schistosomiasis and soil-transmitted helminths, respectively. Although historical data identifies areas of transmission of these neglected tropical diseases (NTDs), there is a need to update epidemiological data. For this reason, Namibia adopted a new protocol for mapping of schistosomiasis and geohelminths, formally integrating rapid diagnostic tests (RDTs) for infections and morbidity. In this article, we explain the protocol in detail, and introduce the concept of ‘mapping resolution’, as well as present results and treatment recommendations for northern Namibia.Methods/Findings/InterpretationThis new protocol allowed a large sample to be surveyed (N = 17 896 children from 299 schools) at relatively low cost (7 USD per person mapped) and very quickly (28 working days). All children were analysed by RDTs, but only a sub-sample was also diagnosed by light microscopy. Overall prevalence of schistosomiasis in the surveyed areas was 9.0%, highly associated with poorer access to potable water (OR = 1.5, P<0.001) and defective (OR = 1.2, P<0.001) or absent sanitation infrastructure (OR = 2.0, P<0.001). Overall prevalence of geohelminths, more particularly hookworm infection, was 12.2%, highly associated with presence of faecal occult blood (OR = 1.9, P<0.001). Prevalence maps were produced and hot spots identified to better guide the national programme in drug administration, as well as targeted improvements in water, sanitation and hygiene. The RDTs employed (circulating cathodic antigen and microhaematuria for Schistosoma mansoni and S. haematobium, respectively) performed well, with sensitivities above 80% and specificities above 95%.Conclusion/SignificanceThis protocol is cost-effective and sensitive to budget limitations and the potential economic and logistical strains placed on the national Ministries of Health. Here we present a high resolution map of disease prevalence levels, and treatment regimens are recommended.

Performance of POC-CCA® in diagnosis of schistosomiasis mansoni in individuals with low parasite burden

“…Treating trace results as positive may result in over-treatment; however, in low transmission areas, if there is sufficient praziquantel available, this may be preferable to under-treatment for achieving elimination. Souza-Figueiredo et al (40) showed that, in a low transmission setting (prevalence below 10%), the urine CCA test performed better if the observer considered trace results as negative cases. If trace results are considered to represent positive cases, the test becomes more sensitive but also, as a consequence, less specific.…”

Urogenital schistosomiasis transmission on Unguja Island, Zanzibar: characterisation of persistent hot-spots

“…Multiple factors that can significantly increase the risk of infection with schistosomes might be important drivers for the existence and persistence of schistosomiasis transmission hot-spot areas and their resilience to PC and other intervention measures such as snail control and health education. These risk factors include living in close proximity to a freshwater body containing intermediate host snail species [17, 21, 24], frequent and intense contact of humans with natural freshwater [17, 25], lack of drinking water sources and latrines in schools [25] and the construction of agricultural water schemes [26]. Also “super-spreaders”, potentially untreated or treated and then re-infected people that harbour heavy infections, might contribute to the perpetuation or resurgence of transmission [27, 28].…”

Diagnosis of Schistosoma mansoni infections: what are the choices in Brazilian low-endemic areas?

“…Souza-Figueiredo et al 110 previously reported that POC-CCA® results are more in agreement with those of K-K when traces are considered negative in low-endemic areas. This is not considered in Brazilian studies, however, even if a reference method is adopted.…”