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Fig. 2 | Infectious Diseases of Poverty

Fig. 2

From: Towards interruption of schistosomiasis transmission in sub-Saharan Africa: developing an appropriate environmental surveillance framework to guide and to support ‘end game’ interventions

Fig. 2

Key environmental aspects in schistosome transmission as framed by contamination- and exposure- related behaviours. a Image of Barombi Mbo, South-West Cameroon a small linear village recently sampled in May 2016 during a conjoint parastiological and malacology survey, finding the prevalence of egg-patent S. haematobium infection < 10%. Snails were searched for at six collecting locations (sites 1–6), only B. forskalii and B. truncatus were found at sites 1 and 2, with an average daily collection at each site inspection of 11 and 57 snails over a three day period, respectively. The survey highlights the small-scale heterogenities typical of schistosomiasis. b A schematic of the three phased progress of interventions from morbidity to transmission control then interuption of transmission, as prevalence of egg-patent infection declines as indicated by the blue section. At the sametime the miracidial input will likely concomittantly decline into the local snail fauna, in host (H) or non-host (NH) snails, respectively. Contrary to host snails, non-host snails do not produce cercariae hence play no later role in exposure-related transmission. Measuring and comparing the prevalence of schistosome DNA in H and NH species could provide information in the context of contamination-related and exposure-related measures at different stages during this transition. Conceptually, there should always be additional H snails that are patently (stage II) or pre-patently (stage III) infected and carry schistosome infections. Note that as the human miracidial input declines zoonotic sources may be more obvious and the need for species- and population-specific schistosome probes becomes essential

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