Parasitology

Research Article

Spatial and temporal heterogeneity in the population dynamics of Bulinus globosus and Biomphalaria pfeifferi and in the epidemiology of their infection with schistosomes

M. E. J. Woolhousea1 and S. K. Chandiwanaa2

a1 Department of Pure and Applied Biology, Imperial College, Prince Consort Road, London SW7 2BB and Department of Biological Sciences, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, ZW

a2 Blair Research Laboratories, P.O. Box 8105, Causeway, Harare, ZW

Abstract

Populations of Bulinus globosus and Biomphalaria pfeifferi were studied in a river habitat in Zimbabwe over a period of 12 months. Data were obtained on the prevalences of infections of Schistosoma haematobium (also S. mattheei) and S. mansoni respectively. Population parameters showed the following patterns for both snail species. (1) A patchy distribution correlated with the distributions of aquatic plants. (2) Life-expectancies of only a few weeks. (3) Recruitment rates correlated with water temperature and showing a distinct seasonal peak. (4) Spatial variation in recruitment. (5) A redistribution of snails during the rainy season. Epidemiological parameters showed the following patterns. (1) Large seasonal variations in the prevalence of patent infections. (2) Evidence from size-prevalence curves that suggests a variable force-of-infection from man to snail, correlated with water temperature. (3) Prevalences of infection that were higher in the vicinity of (±60 m from) major water contact sites. Local prevalences of infection for B. globosus sometimes exceeded 50% and may have approached 100% if pre-patent infections are included. Snail numbers may limit transmission at these locations. Attention is drawn to the need to make field observations at an appropriate spatial scale and also to the implications for the effectiveness of focal snail control as a means of reducing transmission.

(Accepted July 13 1988)

Key words

  • Bulinus globosus;
  • Biomphalaria pfeifferi;
  • population dynamics;
  • epidemiology;
  • Schistosoma haematobium;
  • Schistosoma mansoni
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