The Effect of Climate Change and the Snail-Schistosome Cycle in Transmission and Bio-Control of Schistosomiasis in Sub-Saharan Africa

Abstract

In the next century, global warming, due to changes in climatic factors, is expected to have an enormous influence on the interactions between pathogens and their hosts. Over the years, the rate at which vector-borne diseases and their transmission dynamics modify and develop has been shown to be highly dependent to a certain extent on changes in temperature and geographical distribution. Schistosomiasis has been recognized as a tropical and neglected vector-borne disease whose rate of infection has been predicted to be elevated worldwide, especially in sub-Saharan Africa; the region currently with the highest proportion of people at risk, due to changes in climate. This review not only suggests the need to develop an efficient and effective model that will predict Schistosoma spp. population dynamics but seeks to evaluate the effectiveness of several current control strategies. The design of a framework model to predict and accommodate the future incidence of schistosomiasis in human population dynamics in sub-Saharan Africa is proposed. The impact of climate change on schistosomiasis transmission as well as the distribution of several freshwater snails responsible for the transmission of Schistosoma parasites in the region is also reviewed. Lastly, this article advocates for modelling several control mechanisms for schistosomiasis in sub-Saharan Africa so as to tackle the re-infection of the disease, even after treating infected people with praziquantel, the first-line treatment drug for schistosomiasis.

Keywords: Biomphalaria spp.; Bulinus spp.; Schistosomiasis; cercariae; climate change; sub-Saharan Africa.

Figure 1

Proposed model eliciting effects of change in climatic factors on Schistosomiasis transmission. 1. Changes in climatic factors are an essential determinant in the production and development of snails, as well as the production and development time of miracidia and cercaria in the intermediate host (snails) and in freshwater depends on climate variability, 2. The snails. as well as miracidia and cercariae in freshwater and intermediate hosts. depends on a change in climatic factors to survive, 3. Climate changes pose a serious influence on the fecundity of the snails and hatching of schistosomes eggs into miracidia, 4. Replication of miracidia in the intermediate host to form sporocyte which in turn produce cercaria, 5. Increase in survival rate leads to an increase in fecundity rate, 6. Climate change enhances the rapid reproduction of snails and the rapid metamorphosis of miracidia into cercaria in the intermediate host, 7. Increase in the fecundity rate of snails enhances the transmission of schistosomiasis by increasing the production number of cercaria within snails, 8. The cercaria penetrates into the definitive human host, thereby metamorphosing into schistosomula that develop into adult worms which lay eggs that are responsible for the morbidity and mortality resulting from this disease.