Updating estimates ofPlasmodium knowlesimalaria risk in response to changing land use patterns across Southeast Asia

Abstract

BackgroundPlasmodium knowlesiis a zoonotic parasite that causes malaria in humans. The pathogen has a natural host reservoir in certain macaque species and is transmitted to humans via mosquitoes of theAnophelesLeucosphyrus Group. The risk of humanP. knowlesiinfection varies across Southeast Asia and is dependent upon environmental factors. Understanding this geographic variation in risk is important both for enabling appropriate diagnosis and treatment of the disease and for improving the planning and evaluation of malaria elimination. However, the data available onP. knowlesioccurrence are biased towards regions with greater surveillance and sampling effort. Predicting the spatial variation in risk ofP. knowlesimalaria requires methods that can both incorporate environmental risk factors and account for spatial bias in detection.Methods & ResultsWe extend and apply an environmental niche modelling framework as implemented by a previous mapping study ofP. knowlesitransmission risk which included data up to 2015. We reviewed the literature from October 2015 through to March 2020 and identified 264 new records ofP. knowlesi, with a total of 524 occurrences included in the current study following consolidation with the 2015 study. The modelling framework used in the 2015 study was extended, with changes including the addition of new covariates to capture the effect of deforestation and urbanisation onP. knowlesitransmission.DiscussionOur map ofP. knowlesirelative transmission suitability estimates that the risk posed by the pathogen is highest in Malaysia and Indonesia, with localised areas of high risk also predicted in the Greater Mekong Subregion, The Philippines and Northeast India. These results highlight areas of priority forP. knowlesisurveillance and prospective sampling to address the challenge the disease poses to malaria elimination planning.Author SummaryPlasmodium knowlesiis a parasite that can cause malaria when it infects humans. Although most people do not experience severe illness fromPlasmodium knowlesiinfection, a small number will develop serious or even fatal disease. The parasite is found naturally in some monkeys throughout Southeast Asia, and spreads from these monkeys to humans through mosquitoes. Previous research predicted where the risk of being infected is highest according to what we know about the environment across Southeast Asia, such as if there are forests in an area or if the altitude is high. In this work, we extend this previous research with more up-to-date data on environmental conditions and infections to predict the risk of being infected withPlasmodium knowlesi. We show that the riskPlasmodium knowlesiposes to humans is high across much of Southeast Asia, and that the disease will continue to challenge national goals to eliminate malaria.

The economic burden of zoonoticPlasmodium knowlesimalaria on households in Sabah, Malaysia compared to malaria from human-onlyPlasmodiumspecies

“…Rapid changes in land use have created complex environments, including reduced forest cover and biodiversity [12, 20], which have altered the interaction and parasite transmission dynamics between humans, mosquito vectors and macaque hosts [12]. P. knowlesi transmission is now demonstrated to occur in other locations in Southeast Asian locations [11]; without adequate control measures, the medical costs and indirect productivity losses will continue to place a substantial economic burden on patients and their families.…”

“…P. knowlesi infection also carries a high risk of severe disease, estimated at 6-9% of symptomatic cases presenting to health facilities in East Malaysia, comparable with previous risk for falciparum malaria in sympatric areas [5, 8–10]. Human infections with P. knowlesi occur in areas inhabited by natural macaque hosts where it is transmitted to humans via Anopheles Leucosphyrus Group mosquito vectors [11]. Due to the lack of effectiveness of traditional malaria public health control methods for zoonotic transmission primarily at the forest-edge [12, 13], the need for inter-sectoral approaches has been recommended for P. knowlesi [14].…”

Genomic epidemiology ofPlasmodium knowlesireveals putative genetic drivers of adaptation in Malaysia

“…P. knowlesi infections can cause severe, life-threatening malaria, with a case fatality similar to that of P. falciparum in Southeast Asia despite comparatively lower levels of parasitemia (4,5). The recent increased reporting of P. knowlesi infections in Southeast Asia has been strongly linked with the encroachment of humans on previously intact habitats of their natural macaque reservoir hosts (6). Zoonotic transmission of P. knowlesi is thought to occur largely in response to increasingly fragmented landscapes as a result of land clearing and associated agricultural activities, with increased exposure in at-risk workers and local populations in endemic areas to both pig-tailed (Macaca nemestrina) and long-tailed (M. fascicularis) macaques, and the Anopheles Leucosphyrus Group mosquito vectors (7,8).…”