Anthropisation and malaria transmission in rural Cambodia
Author: Pephey, Anaïs
Under the direction of: Benoit Witkowski
University of Montpellier
Texte français
Keywords: Epidemiology, Cambodia Malaria, Transmission, Anthropization, Epidemiology, Cambodia.
Abstract
Cases of malaria are down overall, including in the Greater Mekong sub-region, which aims to eliminate the disease by 2030. Cambodia, after implementing the use of insecticide-treated mosquito nets throughout the territory, now faces residual malaria transmission mainly around international borders and forests. The vectors live in wooded areas and infect forest workers as well as migrant populations, maintaining transmission despite the efforts of the teams in charge of detecting and treating cases of malaria. Rapid deforestation and economic growth could affect transmission, but their potential repercussions have been little or not studied or described in the sub-region, although their understanding may be necessary for effective and sustainable malaria elimination. To this end, this PhD proposes to observe and understand the dynamics of malaria in Cambodia in order to determine where, when and how the contact between the populations at risk and the vectors is created and its link with anthropization. The first chapter of this thesis focuses on environmental changes and the mobility of at-risk populations in the study area. Using high-resolution satellite images, we quantified the deforestation of an area particularly affected by malaria in the northeast of the country. We have characterized the evolution of forest cover, fragmentation and landscape diversity over 30 years, and gathered the available data on malaria cases for this same period. A cross-sectional study, a cohort and monitoring of at-risk populations in the same study area have made it possible to describe and better understand the behaviors and mobility associated with an infection, through the implementation of techniques frequently used in Cambodia. , such as questionnaires, and innovative, such as GPS beacons or the quantification of anti-saliva antibodies from Anopheles by ELISA. The second chapter is dedicated to the diversity, abundance and prevalence of mosquito vectors. Three types of traps (collection on human bait, double net trap and interception traps) and the collection of larvae along transects were used in different environments following a gradient of anthropization : villages, fields, plantations of trees and forests. . After identification of the Anopheles species collected, we determined the prevalence of Plasmodium in the mosquito population, in order to study which environmental factors affected the presence of human Plasmodium and the abundance of the vectors. We also compared the accuracy of morphological identifications versus molecular identifications. Finally, we identified the origin of blood meals extracted from the abdomens of fed females to determine if certain environmental or species factors were associated with cannibalism. The third and final chapter of this thesis focused on the nature of malaria transmission itself. To characterize the structure of parasite populations circulating between humans and vectors, we sequenced samples of Plasmodium falciparum and Plasmodium vivax from GPS tracking of forest workers and mosquitoes from our collections using the deep amplicon sequencing method. The genetic data associated with this sequencing will make it possible to understand the genetics of parasite populations as well as the nature of the clones making up the infections. Overall, this project is placed at the intersection of geography, epidemiology, entomology and genomics with the objective of completing knowledge on the relationship between anthropization and malaria transmission in Cambodia.
