Over the past ten years, morbidity and mortality due to malaria have fallen considerably in Cambodia. Although in 2018 the country declared zero mortality from malaria for the first time, its elimination remains in jeopardy today.
“In Cambodia, unlike Africa, the majority of mosquitoes that transmit malaria are found in forest areas. This is where people are infected,” explains Patrice Piola, a researcher at the Institut Pasteur du Cambodge. The persistence of the infectious disease in rural Cambodia is therefore mainly attributed to people passing through or living in forests. However, the mechanisms of malaria transmission in forest environments have not yet been studied, and probably present several specificities, implying control measures specific to the forest and its populations.
Reaching remote populations
In Cambodia, the mobile and migrant population of forest workers, such as woodcutters, originates from the country’s remote provinces, but also from neighboring countries (Vietnam, Thailand and Laos). Around 7,000 forestry workers have been identified in the country, 90% of them men. These workers leave their villages in the morning to work in the forests, sometimes for days on end. In Cambodia, the main risk factor associated with malaria is the greater nocturnal activity of malaria mosquitoes. The families of these workers, estimated at 30,000 for the forests studied by the Institut Pasteur du Cambodge, live in or near the forests. Although they have access to the health system, many suffer from malnutrition and diseases such as tuberculosis and malaria. In addition, forest dwellings are often completely or partially open to the outside, and impregnated mosquito nets are not fully used. This increases the risk of malaria infection imported from the forest.
Faced with this situation, the Institut Pasteur du Cambodge set out to study the mechanisms of malaria transmission in the forest, in order to improve strategies for rapidly eliminating the parasite reservoir through community-based interventions in the forests. “First, we need to understand the epidemiology of malaria in forest areas, and then eliminate it with appropriate interventions. Currently, action against malaria takes place outside the forests. Since 2018, community agents have been moving into the forest without staying there. The permanent installation of our project in the heart of the reservoir of this disease gives us hope that it will be possible to bring it down in the forest and in the surrounding health centers. For this project, we have therefore chosen to collaborate with woodcutters, whom we equip and train. Our study forests are sectorized, and in each sector a worker carries out the study procedures, which mainly consist of an electronic questionnaire and blood sampling,” explains Patrice Piola. Worth over a million euros and lasting almost three years, this project is the fruit of a partnership with the national malaria control program and the NGO Partners for Development.
Documenting and preventing malaria transmission
In 2019, the Institut Pasteur du Cambodge and its partners set up the first network of forest workers specialized in malaria control within forests. Nearly 600 square kilometers of forest areas in Mondulkiri, Stung Treng and Kratie were covered by 30 agents, recruited from among the forest dwellers themselves. They worked in close collaboration with local communities, collecting data from 3,179 workers. This has enabled us to better understand the epidemiology of malaria in the forest areas studied.
In 2020, the network’s workers offered to test their peers: those found to be malaria-positive were treated. At the same time, a monthly intermittent preventive treatment was prescribed to forest workers. The effectiveness of the preventive treatment was evaluated in three cross-sectional studies between September 2020 and January 2021. In October 2020, following the rainy season with the highest annual malaria notifications, only 28 cases of Plasmodium falciparum, the malaria species responsible for fatal cases, were notified in all Cambodian health centers. The initial results of the study, together with recommendations for reducing the incidence of malaria in Cambodia’s forests, have been published by the Institut Pasteur du Cambodge (Choosing interventions to eliminate forest malaria: preliminary results of two operational research studies inside Cambodian forests).
