**3. Snail borne diseases**

There are different intermediate host snail species in the world freshwater bodies which cause snail borne parasitic diseases like schistosomiasis, paragonimiasis, fascioliasis, fasciolopsiasis, angiostrongyliasis, clonorchiasis, and opisthorchiasis. These diseases are the most important parasitic disease which remains crucial to public health issues worldwide, mainly in developing countries. Millions of people in 90 countries have suffered from snail borne disease, in which snails are intermediate hosts and transmitting vectors. These diseases also resulting in extensive socioeconomic burdens in many tropical and sub-tropical countries [1].

Specifically, human schistosomiasis is one of the most prevalent parasitic infections in the world and found in 52 countries. A report from WHO indicated that 219.9 million people worldwide are estimated to be affected by schistosomiasis, of which it is estimated that at least 90.4% of those requiring treatment for schistosomiasis live in Africa. This disease caused a loss of 2.5 million disability-adjusted life years (DALYs) [6]. It is the second most widespread parasitic disease after malaria and killing an estimated 300,000 people each year in the African region alone and 163 million population need treatment in sub-Saharan Africa [56, 57].

Schistosomiasis is caused by six species of trematodes from the genus *Schistosoma*: *Schistosoma mansoni*, *S. haematobium*, *S. japonicum*, *S. intercalatum*, *S. guineensis* and *S. mekongi*. The predominant causes of disease are *S. mansoni* and *S. haematobium* in tropical and subtropical regions, particularly in sub-Saharan Africa [6]. *Schistosoma mansoni* and *S. haematobium* trematodes are transmitted by two primary snail species of the genus *Biomphalaria* and *Bulinus* respectively, which are widely distributed throughout African countries [58].

Environmental and endogenous variables influence the development of *Schistosoma mansoni*'s life cycle in its intermediate host [58]. Mollusk infections occur in freshwater bodies contaminated by schistosome-infected people's feces. The existence of the Biomphalaria mollusk, as well as lack of or inadequate sanitation, human cultural habits, and the parasite's life cycle, all contribute to the parasite's persistence and, as a result, the disease's geographic spread [59–61].

The complete spectrum of direct and indirect effects on host and parasite life histories determines the impact of abiotic environmental factors on infectious disease dynamics. Importantly, these effects will go beyond a simple shift in host or parasite geographic distribution to involve a considerable modification in the physiological and temporal interaction between host and parasites, thereby altering disease dynamics in natural populations [62].
