Estimating the prevalence and intensity of Schistosoma mansoni infection among rural communities in Western Tanzania: the influence of sampling strategy and statistical approach

Bakuza, J. S., Denwood, M. J., Nkwengulila, G. and Mable, B. K. (2017) Estimating the prevalence and intensity of Schistosoma mansoni infection among rural communities in Western Tanzania: the influence of sampling strategy and statistical approach. PLoS Neglected Tropical Diseases, 11(9), e0005937. (doi:10.1371/journal.pntd.0005937) (PMID:28934206) (PMCID:PMC5626504)

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Abstract

Background: Schistosoma mansoni is a parasite of major public health importance in developing countries, where it causes a neglected tropical disease known as intestinal schistosomiasis. However, the distribution of the parasite within many endemic regions is currently unknown, which hinders effective control. The purpose of this study was to characterize the prevalence and intensity of infection of S. mansoni in a remote area of western Tanzania. Methodology/Principal findings: Stool samples were collected from 192 children and 147 adults residing in Gombe National Park and four nearby villages. Children were actively sampled in local schools, and adults were sampled passively by voluntary presentation at the local health clinics. The two datasets were therefore analysed separately. Faecal worm egg count (FWEC) data were analysed using negative binomial and zero-inflated negative binomial (ZINB) models with explanatory variables of site, sex, and age. The ZINB models indicated that a substantial proportion of the observed zero FWEC reflected a failure to detect eggs in truly infected individuals, meaning that the estimated true prevalence was much higher than the apparent prevalence as calculated based on the simple proportion of non-zero FWEC. For the passively sampled data from adults, the data were consistent with close to 100% true prevalence of infection. Both the prevalence and intensity of infection differed significantly between sites, but there were no significant associations with sex or age. Conclusions/Significance: Overall, our data suggest a more widespread distribution of S. mansoni in this part of Tanzania than was previously thought. The apparent prevalence estimates substantially under-estimated the true prevalence as determined by the ZINB models, and the two types of sampling strategies also resulted in differing conclusions regarding prevalence of infection. We therefore recommend that future surveillance programmes designed to assess risk factors should use active sampling whenever possible, in order to avoid the self-selection bias associated with passive sampling.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Mable, Professor Barbara and Denwood, Dr Matthew and Bakuza, Mr Jared
Authors: Bakuza, J. S., Denwood, M. J., Nkwengulila, G., and Mable, B. K.
College/School:College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation
College of Medical Veterinary and Life Sciences > School of Veterinary Medicine
Journal Name:PLoS Neglected Tropical Diseases
Publisher:Public Library of Science
ISSN:1935-2735
ISSN (Online):1935-2735
Copyright Holders:Copyright © 2017 Bakuza et al.
First Published:First published in PLoS Neglected Tropical Diseases 11(9): e0005937
Publisher Policy:Reproduced under a Creative Commons license

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
374091Genomes, pathogens and mate choice - implications for the evolution and maintenance of genetic diversityBarbara MableNatural Environment Research Council (NERC)NE/B50094X/1RI BIODIVERSITY ANIMAL HEALTH & COMPMED