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The relationship between the frequency distribution of Ascaris lumbricoides and the prevalence and intensity of infection in human communities

Published online by Cambridge University Press:  06 April 2009

H. L. Guyatt
Affiliation:
Parasite Epidemiology Research Group, Department of Biology, Imperial College, University of London, Prince Consort Road, London SW7 2BB
D. A. P. Bundy
Affiliation:
Parasite Epidemiology Research Group, Department of Biology, Imperial College, University of London, Prince Consort Road, London SW7 2BB
G. F. Medley
Affiliation:
Parasite Epidemiology Research Group, Department of Biology, Imperial College, University of London, Prince Consort Road, London SW7 2BB
B. T. Grenfell
Affiliation:
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ

Summary

Observed field data from a range of geographically distinct human communities suggest a consistent non-linear relationship between prevalence and mean intensity of Ascaris lumbricoides infection. Utilizing the negative binomial distribution as a description of observed aggregation, maximum-likelihood analysis reveals that the degree of aggregation is a negative linear function of mean worm burden. The factors responsible for this relationship in human populations require further study but may involve some combination of (i) density-dependent reduction in worm numbers within individuals, (ii) density-dependent parasite-induced host mortality or (iii) self-treatment by heavily infected hosts. Variability in the degree of aggregation appears dependent on the level of infection in a community and independent of geographical differences in the host or parasite populations.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1990

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