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On the use of age-intensity data to detect immunity to parasitic infections, with special reference to Schistosoma mansoni in Kenya

Published online by Cambridge University Press:  06 April 2009

A. J. C. Fulford ,
A. E. Butterworth ,
R. F. Sturrock  and
J. H. Ouma
A. J. C. Fulford
Affiliation:
Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP
A. E. Butterworth
Affiliation:
Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP
R. F. Sturrock
Affiliation:
Department of Medical Parasitology, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT
J. H. Ouma
Affiliation:
Divison of Vector-Borne Diseases, Ministry of Health, P.O. Box 20750, Nairobi, Kenya
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Summary

We consider two phenomena, related to the host age-intensity profiles of parasitic infections, which have been suggested to be indicative of acquired immunity: (i) a lower age of peak intensity among more intensely infected hosts; and (ii) a decline with age in the dispersion of the distribution of parasites between hosts. We demonstrate that these phenomena occur among Kenyan schoolchildren infected with Schistosoma mansoni, although the magnitude of both is small. We also examine the mathematical models underlying these predictions and conclude that both phenomena are possible in the absence of acquired immunity or, indeed, in the absence of any density-dependent effect. In our opinion, insufficient attention has been focused upon mathematical models, describing the null hypothesis, i.e. density-independent models. In particular, we regard the usual assumptions made for the two stochastic components of these models, describing the heterogeneity between hosts and the probabilistic nature of infection and death of parasites, as too rigid and unrealistic. We demonstrate that deviation from these assumptions undermines the qualitative distinctions between models which describe acquired immunity or density dependence and those which are density-independent.

Keywords

Schistosoma mansoniacquired immunityage-intensity profilemathematical modeldensity dependencenegative binomial
Type
Research Article
Information
Parasitology , Volume 105 , Issue 2 , October 1992 , pp. 219 - 227
Copyright
Copyright © Cambridge University Press 1992

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