Abstract
BackgroundPlasmodium knowlesi is a zoonotic pathogen, transmitted among macaques and to humans by anopheline mosquitoes. Information on P. knowlesi malaria is lacking in most regions so the first step to understand the geographical distribution of disease risk is to define the distributions of the reservoir and vector species.MethodsWe used macaque and mosquito species presence data, background data that captured sampling bias in the presence data, a boosted regression tree model and environmental datasets, including annual data for land classes, to predict the distributions of each vector and host species. We then compared the predicted distribution of each species with cover of each land class.ResultsFine-scale distribution maps were generated for three macaque host species (Macaca fascicularis, M. nemestrina and M. leonina) and two mosquito vector complexes (the Dirus Complex and the Leucosphyrus Complex). The Leucosphyrus Complex was predicted to occur in areas with disturbed, but not intact, forest cover (> 60 % tree cover) whereas the Dirus Complex was predicted to occur in areas with 10–100 % tree cover as well as vegetation mosaics and cropland. Of the macaque species, M. nemestrina was mainly predicted to occur in forested areas whereas M. fascicularis was predicted to occur in vegetation mosaics, cropland, wetland and urban areas in addition to forested areas.ConclusionsThe predicted M. fascicularis distribution encompassed a wide range of habitats where humans are found. This is of most significance in the northern part of its range where members of the Dirus Complex are the main P. knowlesi vectors because these mosquitoes were also predicted to occur in a wider range of habitats. Our results support the hypothesis that conversion of intact forest into disturbed forest (for example plantations or timber concessions), or the creation of vegetation mosaics, will increase the probability that members of the Leucosphyrus Complex occur at these locations, as well as bringing humans into these areas. An explicit analysis of disease risk itself using infection data is required to explore this further. The species distributions generated here can now be included in future analyses of P. knowlesi infection risk.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1527-0) contains supplementary material, which is available to authorized users.
Highlights
Plasmodium knowlesi is a zoonotic pathogen, transmitted among macaques and to humans by anopheline mosquitoes
Our aim was to produce predicted species distributions, based on empirical data, that could be used in future studies, combined with what data there is on P. knowlesi infections at different locations, to predict geographical variation in disease risk in future studies
Notifications of knowlesi malaria cases increased in Malaysian Borneo between 1992 and 2011 [61] and our results indicate the conversion of intact forest to disturbed forest, and the resulting impact on the probability of encountering members of the Leucosphyrus Complex, could be a factor here
Summary
Plasmodium knowlesi is a zoonotic pathogen, transmitted among macaques and to humans by anopheline mosquitoes. Information on P. knowlesi malaria is lacking in most regions so the first step to understand the geographical distribution of disease risk is to define the distributions of the reservoir and vector species. Outside Malaysia, human cases have been reported from a small number of dispersed locations [3, 4] but the distribution of P. knowlesi in these countries is largely unknown. There are far more reports of macaque and mosquito populations, which provides an opportunity to use these distributions to refine estimates of the geographical distribution of knowlesi malaria. No study has analysed the relationship between forest cover and the distributions of the primary P. knowlesi host or vector species, across the ranges of these species, limiting our ability to understand the risk factors for disease transmission
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