In Altamira, in the Brazilian Amazon, an ambitious campaign to combat malaria had almost achieved the impossible. Between 2013 and 2017, in the wake of the construction of one of the largest hydroelectric dams in the world named Belo Monte, cases of malaria fell impressively: from 1,200 cases in 2013, only around sixty remained at the end of the program. The respite, however, was short-lived. A few years later, infections started to rise again, affecting more than 700 people each year, mainly in rural areas.
In a study published July 9 in the journal GeoHealth, scientists sifted through more than fifteen years of malaria surveillance data. They cross-referenced them with satellite images of the forests surrounding Altamira, where vast areas have been cleared to make way for cattle breeding and urbanization. Previous work had already established a link between the spread of the disease and deforestation or the construction of dams. These structures promote the development of habitats appreciated by mosquito larvae, which live at the edges of forests.
The scientists’ conclusions are clear: the resurgence of malaria in Altamira cannot be explained solely by deforestation and work linked to the mega-dam. Maintaining surveillance in high-risk areas is just as essential as the initial reduction program, Live Science supports.
During construction on the dam, thousands of workers flocked to the site. The initiative to combat malaria then included several key measures to limit the risk of an epidemic: spraying of insecticides inside homes, distribution of mosquito nets, as well as the generalization of diagnosis and rapid treatment of patients. Measures which ended once the construction site was completed.
Mosquitoes contract the parasite that causes malaria by feeding on the blood of infected people, before transmitting it to other individuals through bites. Rapidly identifying and treating patients therefore makes it possible to break the chain of transmission.
Living on the edge of the forest, a risk factor
To understand why the disease returned, researchers compared clinical records from 150 health centers in the Altamira region with data on temperature, forest cover and precipitation. Their objective was to identify areas conducive to the breeding of mosquitoes and the development of parasites. The scientists also estimated the travel time between each infection center and the nearest city. According to their observations, the closer a person lives to the edge of the forest, the greater their risk of contracting malaria.
Before the construction of the dam, most of those infected lived in the heart of the city. Today, this trend has been reversed. Since 2020, isolated rural households, located on the edge of the forest, have been the most affected. “When the funded program ended, malaria re-emerged in the communities hardest for the health system to reachspecifies Eloise Skinner, epidemiologist at the University of Queensland in Australia and co-author of the study. The city remained protected, most likely because it is easier to ensure and maintain rapid diagnosis and treatment in an urban setting.”
While Brazil aims to eliminate malaria by 2035, the case of Altamaria has dashed some hopes. However, it allows certain conclusions to be drawn. When a population lives sustainably in contact with an environment favorable to the transmission of the parasite, such as ecosystems located at the edge of a forest, ending prevention measures too early can undo years of efforts.
“The take-home message for the 2035 target is not only that eradication requires sustained investment, concludes Eloise Skinner. Where the environment is a risk factor, that risk is predictable. By being prepared from the start, funds can be allocated where they are most needed.” It remains to be seen how the Brazilian authorities will adapt their prevention plans in the fight against malaria.
