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Human Helminth Co-Infection: Analysis of Spatial Patterns and Risk Factors in a Brazilian Community

Pullan, R.L., Bethony, J.M., Geiger, S. M., Cundill, B., Correa-Oliveira, R., Quinnell, R.J., Brooker, S. and Raso, G. (2008) Human Helminth Co-Infection: Analysis of Spatial Patterns and Risk Factors in a Brazilian Community. PLoS Neglected Tropical Diseases, 2 (12). e352. ISSN 1935-2735



Individuals living in areas endemic for helminths are commonly infected with multiple species. Despite increasing emphasis given to the potential health impacts of polyparasitism, few studies have investigated the relative importance of household and environmental factors on the risk of helminth co-infection. Here, we present an investigation of exposure-related risk factors as sources of heterogeneity in the distribution of co-infection with Necator americanus and Schistosoma mansoni in a region of southeastern Brazil.


Cross-sectional parasitological and socio-economic data from a community-based household survey were combined with remotely sensed environmental data using a geographical information system. Geo-statistical methods were used to explore patterns of mono- and co-infection with N. americanus and S. mansoni in the region. Bayesian hierarchical models were then developed to identify risk factors for mono- and co-infection in relation to community-based survey data to assess their roles in explaining observed heterogeneity in mono and co-infection with these two helminth species.


The majority of individuals had N. americanus (71.1%) and/or S. mansoni (50.3%) infection; 41.0% of individuals were co-infected with both helminths. Prevalence of co-infection with these two species varied substantially across the study area, and there was strong evidence of household clustering. Hierarchical multinomial models demonstrated that relative socio-economic status, household crowding, living in the eastern watershed and high Normalized Difference Vegetation Index (NDVI) were significantly associated with N. americanus and S. mansoni co-infection. These risk factors could, however, only account for an estimated 32% of variability between households.


Our results demonstrate that variability in risk of N. americanus and S. mansoni co-infection between households cannot be entirely explained by exposure-related risk factors, emphasizing the possible role of other household factors in the heterogeneous distribution of helminth co-infection. Untangling the relative contribution of intrinsic host factors from household and environmental determinants therefore remains critical to our understanding of helminth epidemiology.

Item Type: Article
Copyright, Publisher and Additional Information: © 2008 Pullan et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Institution: The University of Leeds
Academic Units: The University of Leeds > Faculty of Biological Sciences (Leeds) > Institute of Integrative and Comparative Biology (Leeds)
Depositing User: Sherpa Assistant
Date Deposited: 06 Nov 2009 14:53
Last Modified: 24 Jun 2014 09:34
Published Version: http://dx.doi.org/10.1371/journal.pntd.0000352
Status: Published
Publisher: Public Library of Science
Identification Number: 10.1371/journal.pntd.0000352
URI: http://eprints.whiterose.ac.uk/id/eprint/10097

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