Malaria risk in the Amazon found to be higher in regions with intermediate forest degradation

Amid the preparatory discussions for COP30, which also involve health-related topics, a study contributes to our understanding of the relationship between deforestation and the spread of malaria in the Legal Amazon. This region encompasses all nine Brazilian states in which the Amazon biome is found and was established by the federal government for regional development purposes.

The study shows that intermediate forest cover with 50% deforestation increases human cases of the disease and infection rates by Anopheles mosquitoes, particularly the Nyssorhynchus subgenus.

The study emphasizes the need for targeted interventions that integrate vector control with forest conservation due to the persistent association between deforestation and disease. Malaria is transmitted through the bite of an infected female Anopheles mosquito carrying one or more species of the protozoan Plasmodium. The Anopheles mosquito is also known as nail mosquitoes or marsh mosquitoes.

The researchers conducted field collections at 40 sites in Cruzeiro do Sul, a municipality in the state of Acre located at a deforestation frontier. Along with other towns in the Juruá River Valley, the municipality is considered a persistent hotspot for malaria incidence; interventions over the past decade have not been able to interrupt endemic cycles.

The selected areas represent a gradient of forest cover and deforestation levels. The findings were published in the journal Acta Tropica.

“In our research, we found that the highest risk of malaria transmission occurs when there’s a 50% proportion of native forest near housing, settlements, or population centers. The risk is also high when vegetation is fragmented, allowing greater contact between vectors in the forest and humans.

“On the other hand, it decreases if deforestation is complete, because the environment becomes inhospitable to the vector, or when the forest is restored to levels above 70%, showing the importance of conservation and restoration,” said Gabriel Laporta, the corresponding author of the article and a biologist.

To assess how landscape structure influences transmission, data on mosquito vector abundance and infection rates, as well as malaria cases in humans, were used.

“We found it extremely important to collect not only the vectors, but also blood samples from residents. We tested infectivity in both the vector and host groups. This pattern of transmission risk in the middle of the forest cover gradient appeared in both sets,” Laporta explained.

Laporta, a professor at the FMABC Medical School University Center, has been researching malaria for over 10 years.

In the project, the scientists aim to better understand the persistent cycles of malaria, Chagas disease, and cutaneous leishmaniasis transmission in the context of deforestation. To this end, they are working with integrated geoprocessing modeling and remote sensing technologies combined with information on the incidence of human parasites and the levels of Plasmodium vivax, P. falciparum, Trypanosoma spp., and Leishmania spp. infection in mosquitoes. In total, the project will involve five years of monitoring, with completion scheduled for 2027.

Step-by-step science

In 2021, a group of scientists, including Laporta, published an article in Scientific Reports with findings from a longitudinal spatiotemporal study based on data collected in rural Amazonian settlements. The study showed a higher risk of malaria associated with deforestation.

Two peaks in vector occurrence were detected: the first, involving Plasmodium vivax, Nyssorhynchus darlingi, and local vectors, occurred between 10 and 12 years after the settlements began. The second peak occurred between 36 and 38 years later; however, local vectors were absent, and the other two types were prevalent.

Another study showed that changes to the Amazonian landscape reduced the overall diversity of mosquitoes, allowing Nyssorhynchus darlingi to become dominant.

Constant battle

Deforestation is one of the main causes of malaria spread in endemic countries such as Brazil. Other causes include changes in prevalent mosquito types, loss of biodiversity, and large infrastructure projects that modify natural landscapes, such as hydroelectric plants, mining activities, and urbanization.

Climate change has exacerbated the situation by creating conditions more favorable to the proliferation of mosquitoes through rising temperatures, combined with intense rains and droughts. Measures that can be taken to address these cases include health surveillance systems, attention to the most vulnerable populations, and rapid responses to natural disasters.

In recognition of the fact that the climate crisis directly impacts population health and the need to integrate these two agendas, the presidency of COP30, which will take place in November in Belém, the capital of the state of Pará, has included health in its thematic days.

“Environmental and public health issues seem far apart, but they’re closely connected. One way to intervene in areas such as those we studied would be to promote sustainable initiatives that provide income for residents. Conserved forests have valuable products, but they tend to be less profitable than opening up the land for pasture or agricultural use. Payment for ecosystem services, through the carbon market, for example, may be an alternative.

“A conference such as COP30, which brings together government officials and decision-makers, can be an opportunity to discuss how we’ll replace today’s modus operandi,” Laporta comments.

Malaria is considered a global public health problem and is endemic in the nine states of the Legal Amazon. According to the Ministry of Health, the region accounted for 138,000 of the 142,000 cases registered in the country in 2024.

Through the National Malaria Elimination Plan, Brazil has committed to reaching less than 14,000 cases by 2030 and achieving the final goal by 2035.

The study’s researchers warn that eliminating malaria requires effective treatments and comprehensive vector control strategies. They suggest making the environment less favorable to Anopheles vectors by maintaining biodiversity in conserved forest areas as a potential solution.

“The combination of these ecological factors with improved treatment protocols can leverage malaria elimination efforts,” they write in the article.

The World Health Organization (WHO) estimates that there were 263 million cases of the disease and 597,000 associated deaths worldwide in 2023. About 95% of these deaths occurred in African countries, where access to prevention, detection, and treatment services is still limited.

Individual prevention can be achieved by using mosquito nets and screens to protect against mosquitoes, as well as repellents. Collective measures include sanitation work, filling vector breeding sites, and improving the living conditions of vulnerable populations.

The disease causes fever, chills, tremors, sweating, and headaches. In severe cases, it can lead to seizures, bleeding, and altered consciousness. In Brazil, patients usually receive outpatient treatment from the SUS (Sistema Único de Saúde), the national public health network.