Population dynamics of freshwater gastropods and epidemiology of their helminth infections with emphasis on larval paramphistomes in northern India

Abstract

AbstractNatural populations of the freshwater gastropodsBithynia tentaculata, Gyraulus convexiusculus, Helicorbis coenosus, Indoplanorbis exustus, Lymnaea acuminata, L. luteolaandVivipara bengalensis, were examined from October 1985 to September 1986 at seven transmission sites for paramphistomiasis, fascioliasis and other gastropod-borne infections in Aligarh, northern India. Gastropod diversity and the type and abundance of vegetation were highest at sites containing permanent water bodies. The distributions ofH. coenosusandL. acuminatawere positively correlated with the type and abundance of vegetation at these sites. Ephemeral water bodies containedB. tentaculata, I. exustusandL. luteolawhich were resistant to desiccation during the hot season. Aestivation in these gastropods preceded pronounced breeding activity which began with the onset of the monsoon season. Multivariate analysis (by principal components) was used to investigate relationships between each species of gastropod, their site of occurrence and levels of infection with larval helminths. Seasonal variations in numbers and size class structure in these gastropods were found to influence their prevalences of infection with larval helminths. Metacercarial and cysticercoid infections were more prevalent in smaller size classes ofB. tentaculataandV. bengalensis, whereas larval paramphistomes were more prevalent in larger size classes ofG. convexiusculus, I. exustusandL. luteola. Attempts were made to equate these findings with seasonality in egg shedding by certain species of adult paramphistomes occurring in domestic ruminants.