TY - JOUR

T1 - Frequency distribution of lymphatic Filariasis microfilariae in human populations

T2 - Population processes and statistical estimation

AU - Das, P. K.

AU - Rajagopalan, P. K.

AU - Grenfell, B. T.

AU - Bundy, D. A.P.

N1 - Funding Information:
The Vector Control Research Centre is an institute of the Indian Council of Medical Research. B.G. and D.A.P.B. were supported by the Rockefeller Foundation and the Wellcome Trust. We thank an anonymous referee for very helpful comments.

PY - 1990/12

Y1 - 1990/12

N2 - 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.

AB - 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.

KW - Wuchereria bancrofti

KW - frequency distributions

KW - lymphatic filariasis

KW - microfilariae

KW - truncated negative binomial

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U2 - 10.1017/S0031182000060613

DO - 10.1017/S0031182000060613

M3 - Article

C2 - 2092297

AN - SCOPUS:0025605473

SN - 0031-1820

VL - 101

SP - 417

EP - 427

JO - Parasitology

JF - Parasitology

IS - 3

ER -