Abstract
The zoonotic malaria species Plasmodium knowlesi has become the main cause of human malaria in Malaysian Borneo. Deforestation and associated environmental and population changes have been hypothesized as main drivers of this apparent emergence. We gathered village-level data for P. knowlesi incidence for the districts of Kudat and Kota Marudu in Sabah state, Malaysia, for 2008-2012. We adjusted malaria records from routine reporting systems to reflect the diagnostic uncertainty of microscopy for P. knowlesi. We also developed negative binomial spatial autoregressive models to assess potential associations between P. knowlesi incidence and environmental variables derived from satellite-based remote-sensing data. Marked spatial heterogeneity in P. knowlesi incidence was observed, and village-level numbers of P. knowlesi cases were positively associated with forest cover and historical forest loss in surrounding areas. These results suggest the likelihood that deforestation and associated environmental changes are key drivers in P. knowlesi transmission in these areas.
Highlights
IntroductionMarked spatial heterogeneity in P. knowlesi incidence was observed, and village-level numbers of P. knowlesi cases were positively associated with forest cover and historical forest loss in surrounding areas
The zoonotic malaria species Plasmodium knowlesi has become the main cause of human malaria in Malaysian Borneo
Since the initial description of a large cluster of human infections with the zoonotic malaria Plasmodium knowlesi in Malaysian Borneo in 2004, increasing numbers of P. knowlesi cases have been identified throughout Southeast Asia [1,2]
Summary
Marked spatial heterogeneity in P. knowlesi incidence was observed, and village-level numbers of P. knowlesi cases were positively associated with forest cover and historical forest loss in surrounding areas. These results suggest the likelihood that deforestation and associated environmental changes are key drivers in P. knowlesi transmission in these areas. Fragmentation of existing habitats can increase the frequency of disease transmission by creating transition areas with increased spatial overlap among human, mosquito, and wildlife populations or by altering vector ecology [16,17] The effects of these changes at forest edges have been described for malaria and other vector-borne zoonotic diseases [18,19] but not for P. knowlesi. A previous mathematic modeling study highlighted the potential for increased transmission resulting from increased spatial overlap among people, macaques, and mosquitoes at forest edges [20]
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