Aix Marseille Univ, IRD, INSERM, SESSTIM, ISSPAM, 27 boulevard Jean Moulin, 13005, Marseille, France.
Institut de Recherche pour le Développement, UMR 228 Espace-Dev (IRD, UA, UG, UM, UR), Phnom Penh, Cambodia.
Parasit Vectors. 2023 Sep 12;16(1):324. doi: 10.1186/s13071-023-05915-w.
In the Greater Mekong Subregion, case-control studies and national-level analyses have shown an association between malaria transmission and forest activities. The term 'forest malaria' hides the diversity of ecosystems in the GMS, which likely do not share a uniform malaria risk. To reach malaria elimination goals, it is crucial to document accurately (both spatially and temporally) the influence of environmental factors on malaria to improve resource allocation and policy planning within given areas. The aim of this ecological study is to characterize the association between malaria dynamics and detailed ecological environments determined at village level over a period of several years in Kayin State, Myanmar.
We characterized malaria incidence profiles at village scale based on intra- and inter-annual variations in amplitude, seasonality, and trend over 4 years (2016-2020). Environment was described independently of village localization by overlaying a 2-km hexagonal grid over the region. Specifically, hierarchical classification on principal components, using remote sensing data of high spatial resolution, was used to assign a landscape and a climate type to each grid cell. We used conditional inference trees and random forests to study the association between the malaria incidence profile of each village, climate and landscape. Finally, we constructed eco-epidemiological zones to stratify and map malaria risk in the region by summarizing incidence and environment association information.
We identified a high diversity of landscapes (n = 19) corresponding to a gradient from pristine to highly anthropogenically modified landscapes. Within this diversity of landscapes, only three were associated with malaria-affected profiles. These landscapes were composed of a mosaic of dense and sparse forest fragmented by small agricultural patches. A single climate with moderate rainfall and a temperature range suitable for mosquito presence was also associated with malaria-affected profiles. Based on these environmental associations, we identified three eco-epidemiological zones marked by later persistence of Plasmodium falciparum, high Plasmodium vivax incidence after 2018, or a seasonality pattern in the rainy season.
The term forest malaria covers a multitude of contexts of malaria persistence, dynamics and populations at risk. Intervention planning and surveillance could benefit from consideration of the diversity of landscapes to focus on those specifically associated with malaria transmission.
在大湄公河次区域，病例对照研究和国家级分析表明疟疾传播与森林活动之间存在关联。“森林疟疾”一词掩盖了次区域内各种生态系统的多样性，这些生态系统可能并不具有统一的疟疾风险。为了实现消除疟疾的目标，准确记录（时空上）环境因素对疟疾的影响至关重要，这有助于在特定地区内改善资源分配和政策规划。本生态研究旨在描述在缅甸克钦邦的一个村庄层面上，在几年的时间内，疟疾动态与详细的生态环境之间的关联。
我们根据振幅、季节性和趋势在 4 年内（2016-2020 年）的年内和年际变化，在村庄尺度上描述疟疾发病率特征。环境通过在该区域上叠加一个 2 公里的六边形网格，独立于村庄定位进行描述。具体来说，使用高空间分辨率的遥感数据进行主成分分层分类，将每个网格单元分配给一个景观和气候类型。我们使用条件推理树和随机森林来研究每个村庄的疟疾发病率概况、气候和景观之间的关联。最后，我们构建了生态流行病学区，通过总结发病率和环境关联信息，对该地区的疟疾风险进行分层和制图。
我们确定了 19 种高度多样化的景观（n=19），对应从原始到高度人为改造的景观的梯度。在这种景观多样性中，只有三种与受疟疾影响的景观相关。这些景观由密集和稀疏森林的镶嵌体组成，被小块的农业斑块所分割。一个单一的气候，适度的降雨量和适合蚊子存在的温度范围，也与受疟疾影响的景观相关。基于这些环境关联，我们确定了三个生态流行病学区，标志是疟原虫持续性较高、2018 年后间日疟发病率较高或雨季季节性模式。
森林疟疾一词涵盖了疟疾持续存在、动态和高危人群的多种情况。干预规划和监测可以从考虑景观多样性中受益，重点关注那些与疟疾传播特别相关的景观。
