STUDY ON THE ETHIOPIAN FRESHWATER MOLLUSCS, ESPECIALLY ON IDENTIFICATION, DISTRIBUTION AND ECOLOGY OF VECTOR SNAILS OF HUMAN SCHISTOSOMIASIS

Abstract

Many surveys were carried out in Ethiopia from January 1969 to January 1971 to study freshwater molluscs, especially the intermediate and potential host snails of Schistosoma mansoni and S. haematobium, to collect their ecological data, and to clarify the distribution of the snails in the country. The gastropods collected consisted of two orders, the Prosobranchia and Pulmonata. The former order contained three families (Thiaridae, Viviparidae and Valvatidae) and the latter four families (Planorbidae, Physidae, Lymnaeidae and Ancylidae). The pelecypods contained four families : the Unionidae, Mutelidae, Corbiculidae and Sphaeriidae.Biomphalaria pfeifferi rueppellii and Bulinus (Physopsis) abyssinicus are the most important hosts of S. mansoni and S. haematobium respectively. The freshwater snail species could be grouped into two distibution patterns, one of which is ubiquitous and the other sporadic. B. pfeifferi rueppellii and Bulinus sericinus belong to the former pattern andBiomphalaria sudanica and the members of the subgenus Physopsis to the latter. Pictorial keys were prepared for field workers of schistosomiasis to identify freshwater molluscs in Ethiopia. Habitats of bulinid and biomphalarian snails were ecologically surveyed in connection with the epidemiology of human schistosomiasis. Rain falls and nutritional conditions of habitat appear to influence the abundance and distribution of freshwater snails more seriously than do temperature and pH, but water current affects the distribution frequently. Slight pollution of water brought about by immigration of people with their domestic animals under reclamation plans of land often results in abundance of snails in the waters and subsequently new endemic foci of schistosomiasis.