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Temporal patterns in the epidemiology of schistosome infections of snails: a model for field data

Published online by Cambridge University Press:  06 April 2009

M. E. J. Woolhouse  and
S. K. Chandiwana
M. E. J. Woolhouse
Affiliation:
Department of Pure and Applied Biology, Imperial College, Prince Consort Road, London SW7 2BB
S. K. Chandiwana
Affiliation:
Blair Research Laboratory, P.O. Box 8105, Causeway, Harare, Zimbabwe
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Summary

The prevalence of patent schistosome infections of intermediate host snails often shows seasonal variations. For schistosome, mainlySchistosoma haematobium, infections of Bulinus globosus field data from Zimbabwe show annual ranges in prevalence from 2% to 30%. In this paper a mathematical model is developed for B. globosus population dynamics and the epidemiology of schistosome infection. The model is a discrete-time analogue of a catalytic model, with an added recruitment term. Snail fecundity and survival are functions of age, infection, and temperature. The pre-patent period of infection is dependent on temperature.Parameter values, and relationships with temperature, are taken from earlier field and laboratory studies. The force-of-infection is estimated from analysis of age-prevalence data. Model predictions, making use of temperature data recorded in the field, are in good agreement with observations over a 2-year period at a study site in Zimbabwe. The key features of interest are a fall in the prevalence of patent infections during the cold season and a rapid rise to a peak early in the hot season. This pattern results from the accumulation of pre-patent infections which fail to develop at low temperatures, but mature en masse, together with new infections, after a few weeks at higher temperatures. Model analysis demonstrates that seasonal patterns in the prevalence of patent infections may be due largely to the influence of temperature on the pre-patent period. Seasonal and year-to-year variations in temperature may therefore have significant epidemiological effects.

Keywords

Bulinus globosusepidemiologymathematical modelSchistosoma haematobiumseasonality
Type
Research Article
Information
Parasitology , Volume 100 , Issue 2 , April 1990 , pp. 247 - 253
Copyright
Copyright © Cambridge University Press 1990

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