Destruction of the Amazon rainforest increases the risk of epidemics

Rabies, malaria, dengue, chikungunya, zika, oropouche, mayaro, Saint Louis encephalitis, leptospirosis, leprosy, Chagas, filariasis. These are some of the diseases that originated in animals and that have already triggered relevant cases, outbreaks or epidemics in the Amazon and beyond.

If the biodiversity of the Amazon rainforest is a potential source of diseases, on the other hand, it prevents them from getting out of control, the conclusions of a recent study show.

The work was conducted by Joel Henrique Ellwanger, from UFRGS (Federal University of Rio Grande do Sul), who reviewed hundreds of studies on the relationship between zoonoses (diseases transmitted from animals to humans) and environmental imbalances.

“We are issuing an alert with this article”, says the scientist, who sees “high risks” of the emergence and reemergence of infectious diseases from the Amazon.

The majority of infectious diseases (60%) originated from animal pathogens that jumped to humans (a phenomenon known as “spillover”, in English), such as Sars-CoV-2.

The IEC (Instituto Evandro Chagas), from Belém, isolated 180 different viruses from the Amazon, of which 116 were new to science, 37 associated with human diseases and nine with potential for outbreaks and important epidemics in the country, such as dengue, zika, chikungunya , yellow fever, Saint Louis encephalitis, West Nile fever, mayaro, oropouche and rocio.

The relationship between the emergence of these diseases and environmental changes is well established in science, says Pedro Vasconcelos, a retired virologist at the IEC.

Initial human contact with the pathogen, however, is insufficient to produce an epidemic or pandemic. Social, demographic, biological (such as high transmissibility) and environmental conditions are necessary, ponders Ellwanger.

Environments with high biodiversity “dilute” species at high risk of zoonoses, the so-called “dilution effect”. Mosquitoes, for example, can be eaten by a variety of predators in these environments.

In this sense, a study by USP (University of São Paulo) shows that the reduction of the forest reduced the general diversity of mosquitoes in areas of the Amazon, allowing the dominance of the species that transmits malaria.

Opening of roads is an important vector of deforestation and the reduction of biodiversity, resulting in outbreaks of diseases, as in the construction of the Trans-Amazonian highway, during the dictatorship, with outbreaks of leptospirosis, leishmaniasis, Chagas disease, malaria and mayaro.

Data from Inpe (National Institute for Space Research) show a significant increase in deforestation in the Amazon in the last four years. About 95% of deforestation in the region occurs at a distance of 5.5 km on each side of the road, according to researcher Carlos Nobre, from USP.

Another USP study showed that yellow fever disperses more quickly on roads adjacent to the forest and that forest blocks reduce this dispersion. Gaucho researchers also pointed out that roads act as wind tunnels transporting mosquitoes of the disease.

The construction of the Samuel (Rondônia) and Tucuruí (Pará) hydroelectric plants in the 1980s produced swarms of mosquitoes, according to research by Philip Fearnside, from Inpa (National Institute for Research in the Amazon).

In Tucuruí, Mansonia mosquitoes sprouted from aquatic plants on the surface of the reservoirs. The insect transmits the filariasis worm (or elephantiasis) still present in the Amazon. The phenomenon even led to significant migration of Parakanã Indians and other residents, Fearnside wrote.

“I was in Tucuruí at the time. It was crazy, Inpa researchers used to count 600 mosquito bites per hour on a person”, recalls Fearnside, who is currently studying the environmental impacts of the BR-319 in the Amazon.

In the Peruvian Amazon, an international study showed that the malaria vector (anopheles darlingi) was able to bite 278 times more in the deforested regions.

In the late 1980s, Rondônia came to be known as the “Malaria Capital of the World” due to the epidemic caused by the depredation of the forest. Up to 300,000 cases were registered a year, according to research.

Deforestation also impacts soil microorganisms, increasing their antibiotic resistance genes, making them potential threats to global health and food security, a Brazilian study concluded.

Hunting in the Amazon exposes humans to direct contact with wild animal fluids and viscera. Research has shown that 80% of the inhabitants of urban centers in the Amazon consume wild meat, coming from local markets (80%) or hunted by family members (15%), exceeding 10 thousand tons of meat per year.

In traditional fairs, such as Feira da Panair, in Manaus, animals and wild fruits are exposed to thousands of people daily. The habit of handling and smelling fish to assess quality is common. Contact is intense, similar to what happens in other parts of the world, says Inpa biologist Adalberto Luis Val.

In 2021, the ingestion of contaminated fish caused the “black urine disease” (Haff syndrome) in Amazonian regions. One of the hypotheses is that it is caused by a virus, says Val.

The consumption of armadillos led to outbreaks and cases of leprosy in Pará and systemic mycosis (“disease of the armadillo”) in Ceará and Piauí.

Health surveillance is deficient in the Amazon, assesses Adalberto Luis Val. Qualified researchers and state-of-the-art technology are needed to identify pathogens. Brazil allocates around 3% of the total invested in science and technology to the Amazon, covering an area of ​​60% of the country’s territory, regrets the researcher.

Veterinarian Alessandra Nava works on the front line of Amazonian zoonoses through Fiocruz Amazônia. She draws attention to the increase in human rabies cases in the region, “highly correlated with deforestation,” she says.

Deforestation also paves the way for cattle that, in turn, attract vampire bats, which transmit rabies. The result is that bat bites are increasing in humans and livestock, according to a survey by his team.

_{The Planeta em Transe project is supported by the Open Society Foundations.}