Abstract
Malaria control is an evolving public health concern, especially in times of resistance to insecticides and to antimalarial drugs, as well as changing environmental conditions that are influencing its epidemiology. Most literature demonstrates an increased risk of malaria transmission in areas of active deforestation, but knowledge about the link between land cover evolution and malaria risk is still limited in some parts of the world. In this study, we discuss different methods used for analysing the interaction between deforestation and malaria, then highlight the constraints that can arise in areas where data is lacking. For instance, there is a gap in knowledge in Cambodia about components of transmission, notably missing detailed vector ecology or epidemiology data, in addition to incomplete prevalence data over time. Still, we illustrate the situation by investigating the evolution of land cover and the progression of deforestation within a malaria-endemic area of Cambodia. To do so, we investigated the area by processing high-resolution satellite imagery from 2018 (1.5 m in panchromatic mode and 6 m in multispectral mode) and produced a land use/land cover map, to complete and homogenise existing data from 1988 and from 1998 to 2008 (land use/land cover from high-resolution satellite imagery). From these classifications, we calculated different landscapes metrics to quantify evolution of deforestation, forest fragmentation and landscape diversity. Over the 30-year period, we observed that deforestation keeps expanding, as diversity and fragmentation indices globally increase. Based on these results and the available literature, we question the mechanisms that could be influencing the relationship between land cover and malaria incidence and suggest further analyses to help elucidate how deforestation can affect malaria dynamics.
Highlights
We further examine the considerations around malaria dynamics linked to anthropization in data-scarce conditions and potential methodologies for understanding vector exposure and its interaction with land use
Malaria control efforts achieved a diminution of estimated cases in Cambodia until 2016 (124,137 cases or 8 per 1000 inhabitants), a sharp increase occurred in 2017 and 2018 (202,696 cases or 13 per 1000 inhabitants, and 272,272 cases or 17 per 1000 inhabitants, Figure 4) [37]
Using a GIS approach, some malaria control strategies and elimination programmes have improved their efficacy [74,75,76]. These approaches must be transdisciplinary and include spatiotemporal, ecological as well as social perspectives in order to develop prevention methods able to break the transmission cycle [16]. This investigation illustrates the tremendous anthropogenic land use changes happening in the study area in Cambodia, affecting humans, vectors and their interactions
Summary
Conflicting reports exist on the effect of deforestation on the transmission of vector-borne diseases [1]. Deforestation greatly alters the breeding, abundance and species composition of Anopheles malaria vectors [5,6] This is mediated by changes in the availability of breeding sites for the immature stages [7], as well as differences in resources, predation [8,9], survival [10], fecundity [10] and ecological community structures [7]. Heterogeneity can be affected by fragmentation, the process of a homogenous patch of habitat evolving into smaller and disjoined patches [14] Another aspect of deforestation is landscape diversity, which corresponds to the proportion of patches from different classes. Even with variations among ecological groups and individual species [22], extensive anthropization substantially impacts malaria dynamics [17]
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