Studying Land Cover Changes in a Malaria-Endemic Cambodian District: Considerations and Constraints

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.

Anopheles ecology, genetics and malaria transmission in northern Cambodia

“…Secondly, variability between sampling sites is likely to be an important factor influencing the relative abundance of mosquito species collected. Thirdly, the increased human influence upon Cambodian landscapes including the studied area 55 – 57 is likely to impact mosquito ecology over time and space resulting in large changes in Anopheles communities. Finally, malaria vector control measures might have shifted the Anopheles species involved in malaria parasite transmission as observed in Africa 58 , 59 .…”

The spatial signature of Plasmodium vivax and Plasmodium falciparum infections: quantifying the clustering of infections in cross-sectional surveys and cohort studies

“…The 4200 study participants were 2–79 years old and from randomly sampled households based on a census prior to the survey. Villages of residence were classified into categories of proximity to the forest based on a forest cover remote sensing analysis [ 49 ]. In this and all following included studies, finger-prick blood samples were tested for P. vivax and P. falciparum infections by real-time PCR and GPS locations of households were collected.…”

Asia-Pacific ICEMR: Understanding Malaria Transmission to Accelerate Malaria Elimination in the Asia Pacific Region

“…To do so, we assessed the evolution of the land cover over 30 years and showed a high deforestation rate with wooded areas decreasing from 91% to 47% in our study site. 57 We developed GPS follow-ups of the local populations, which, with the land cover map produced, allows quantification of the different environments visited and the time spent therein. On the basis of these GPS follow-ups, we are now conducting mosquito vector collections in sites with high- and low-human visitation rates.…”