Distributional Trends of Four Species of Freshwater Snails in South Africa With Special Reference to the Intermediate Hosts of Bilharzia

Abstract

Urinary bilharziasis has been known to occur in South Africa since 1864 when it was first discovered by Harley in the vicinity of Humansdorp. Its first local snail intermediate host, now known as Bulinus (Physopsis) africanus (Krauss) was only discovered in 1916 by Becker. In 1957 Mandahl-Barth also recorded Bulinus (Physopsis) globosus (Morelet) from this country whereas Krauss had already described what is now called Biomphalaria pfeifferi from natal in 1848. Up till now these three species are the only established intermediate hosts of Bilharziaknown to be endemic in teh Republic of South Africa. In the course of surveys conducted since 1956 by the Zoology Department of the Potchefstroom University, the Department of State Health Services, the Medical Ecology Centre of the S.A.I.M.R., Johannesburg, and numerous other collaborators and supplemented in 1963-64 by Dr. D. S. Brown of the British Medical Research Council, a large amount of preserved freshwater snail material has been collected and lodged in teh Zoology Department of the Potchefstroom University. Most prominent in these samples, because they are easily recognised as snails by untrained field staff, are the three species already mentioned together with Lymnaea natalensis Krauss and Bulinus (Bulinus) tropicus (Krauss). all these species, incidentally, are either of medical or veterinary importance. The present paper is an attempt to analyse some aspects of the distribution of these species which, in teh subsequent discussion, will be referred to by their generic or subgeneric names. In the analysis no ditinction is made between B. (P.) africanus and B. (P.) globosus. The geographic distribution in south east Africa of the individual species listed here are dealt with by van Eeden, Brown, and Oberholzer (1965). The locality records of that paper are also employed in the present paper, the approach of which is similar to that adopted by van Eeden (1965) which deals with the Transvaal only.