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Frequency distribution of lymphatic filariasis microfilariae in human populations: population processes and statistical estimation

Published online by Cambridge University Press:  06 April 2009

B. T. Grenfell ,
P. K. Das ,
P. K. Rajagopalan  and
D. A. P. Bundy
B. T. Grenfell
Affiliation:
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ
P. K. Das
Affiliation:
Vector Control Research Centre, Medical Complex, Indira Nagar, Pondicherry-605 006, India
P. K. Rajagopalan
Affiliation:
Vector Control Research Centre, Medical Complex, Indira Nagar, Pondicherry-605 006, India
D. A. P. Bundy
Affiliation:
Parasite Epidemiology Research Group, Department of Pure and Applied Biology, Imperial College, LondonSW7 2BB
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Summary

This paper uses simple mathematical models and statistical estimation techniques to analyse the frequency distribution of microfilariae (mf) in blood samples from human populations which are endemic for lymphatic filariasis. The theoretical analysis examines the relationship between microfilarial burdens and the prevalence of adult (macrofilarial) worms in the human host population. The main finding is that a large proportion of observed mf-negatives may be ‘true’ zeros, arising from the absence of macrofilarial infections or unmated adult worms, rather than being attributable to the blood sampling process. The corresponding mf distribution should then follow a Poisson mixture, arising from the sampling of mf positives, with an additional proportion of ‘true’ mf-zeros. This hypothesis is supported by analysis of observed Wuchereria bancrofti mf distributions from Southern India, Japan and Fiji, in which zero-truncated Poisson mixtures fit mf-positive counts more effectively than distributions including the observed zeros. The fits of two Poisson mixtures, the negative binomial and the Sichel distribution, are compared. The Sichel provides a slightly better empirical description of the mf density distribution; reasons for this improvement, and a discussion of the relative merits of the two distributions, are presented. The impact on observed mf distributions of increasing blood sampling volume and extraction efficiency are illustrated via a simple model, and directions for future work are identified.

Keywords

Wuchereria bancroftilymphatic filariasismicrofilariaefrequency distributionstruncated negative binomial

Information

Type
Research Article
Information
Parasitology , Volume 101 , Issue 3 , December 1990 , pp. 417 - 427
Copyright
Copyright © Cambridge University Press 1990

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