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| Background: Freshwater snails are intermediate hosts for a number of trematodes of which some are of medical
and veterinary importance. The trematodes rely on specific species of snails to complete their life cycle; hence the
ecology of the snails is a key element in transmission of the parasites. More than 200 million people are infected
with schistosomes of which 95% live in sub-Saharan Africa and many more are living in areas where transmission is
on-going. Human infection with the Fasciola parasite, usually considered more of veterinary concern, has recently
been recognised as a human health problem. Many countries have implemented health programmes to reduce
morbidity and prevalence of schistosomiasis, and control programmes to mitigate food-borne fascioliasis. As these
programmes are resource demanding, baseline information on disease prevalence and distribution becomes of
great importance. Such information can be made available and put into practice through maps depicting spatial
distribution of the intermediate snail hosts.
Methods: A biology driven model for the freshwater snails Bulinus globosus, Biomphalaria pfeifferi and Lymnaea
natalensis was used to make predictions of snail habitat suitability by including potential underlying environmental
and climatic drivers. The snail observation data originated from a nationwide survey in Zimbabwe and the
prediction model was parameterised with a high resolution Regional Climate Model. Georeferenced prevalence data
on urinary and intestinal schistosomiasis and fascioliasis was used to calibrate the snail habitat suitability predictions to
produce binary maps of snail presence and absence.
Results: Predicted snail habitat suitability across Zimbabwe, as well as the spatial distribution of snails, is reported for
three time slices representative for present (1980-1999) and future climate (2046-2065 and 2080-2099).
Conclusions: It is shown from the current study that snail habitat suitability is highly variable in Zimbabwe, with
distinct high- and low- suitability areas and that temperature may be the main driving factor. It is concluded
that future climate change in Zimbabwe may cause a reduced spatial distribution of suitable habitat of host
snails with a probable exception of Bi. pfeifferi, the intermediate host for intestinal schistosomiasis that may
increase around 2055 before declining towards 2100. | |
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