Experts investigate connection of yellow fever with environmental degradation

A yellow fever outbreak in Minas Gerais state has killed 38 in 2017, according to the latest epidemiological reports from the Minas Gerais Health Secretariat, released on Tuesday (Jan. 24). Other 45 deaths are being investigated.

A group of specialists from different Brazilian states is investigating the yellow fever outbreak and its association with the environmental degradation. They believe that if more information on the subject was provided, the sudden outbreak of the virus could be prevented.

Caused by a virus of the Flaviviridae family, yellow fever is an outbreak disease that can suddenly spread to groups of monkeys and human beings. The reasons for the disease behavior are not well known yet. But specialists believe that it is influenced by the environment. According to Sérgio Lucena, primatologist and zoology professor at the Federal University of Espírito Santo (UFES), the yellow fever outbreak is an ecological phenomenon.

The disease is transmitted in rural and forest areas by the Haemagogus mosquito. In urban areas, it can be transmitted by the Aedes aegypti, which also transmits dengue, Zika virus, and chikungunya fever. However, there are no records of yellow fever transmission in urban settings in Brazil since 1942. In the current outbreak, none of the confirmed, nor suspected cases in Minas Gerais are in urban areas.

Sérgio Lucena explains that the yellow fever virus surrounds some forests and wild regions, reporting a low rate of the disease. Suddenly, it spreads quickly, infecting monkeys and human beings. Animals die first. "They are our sentinels. If the virus spreads to a certain area, the death of monkeys sparks an alert," he said.

For the primatologist, Brazil could have a well-connected system to anticipate these outbreaks, but there is no investment in the sector. If more information was provided, Minas Gerais could, for example, have organized a vaccination campaign in towns located in areas of risk, preventing the disease from spreading. The vaccine is the primary measure for fighting against yellow fever.

Deforestation effects

One of the researchers' hypotheses for the current outbreak is the deforestation that over the years has restricted species of monkeys to very small fragments of forests, which produces several effects. "Impoverished ecosystems may present conditions favorable for the growth of mosquito populations. These outbreaks may be caused by infected mosquitoes finding large populations of monkeys in isolated pieces of the Atlantic forest," reported Sérgio Lucena.

Scientific evidence also suggests that healthy forests with high biodiversity would halt the spread of viruses. Although outbreaks could occur, their intensity could be lower in a preserved environment, as explained Servio Ribeiro, biologist and ecology professor of the Federal University of Ouro Preto (UFOP).

According to the researcher, the population of monkeys is greatly reduced in each outbreak, and it recovers slowly in the following years. "A new outbreak is likely to occur when the virus finds a large amount of monkeys with favorable conditions and genetic characteristics. When there are many infected animals, it is easy to spread the disease to humans," he said.

A forest full of fruits and shadows, with no pollution, helps monkeys grow healthier and stress-free, with a more efficient immune system, offering more resistance to the disease.

Mariana tragedy

On the other hand, Servio Ribeiro considers that there is a remote possibility of association of the tragedy in Mariana (in Minas Gerais state) with the yellow fever outbreak in Minas Gerais. Some of the towns affected by the disease are located close to the Rio Doce valley. Around 60 million m3 of tailings were released after the Samarco mining dam burst in November 2015, leaking all over the Rio Doce river and reaching the coast of Espírito Santo.

"Yellow fever is a disease of the forest. The mosquito that transmits it lays its eggs in trees hollows and bromeliads. The mosquito uses the forest structures, and is not closely connected to large bodies of water and rivers. Towns affected by the disease are located in areas where tailings were not at full strength to tear down the forest," said the biologist.

For Servio Ribeiro, the hypothesis would be more plausible if the outbreak occurred near Mariana, where the impacts of the tragedy were more aggressive and led to deforestation. "In the Rio Doce valley, tailings accumulated on the banks. Of course there was a degradation. But this degradation, based on the knowledge we have, should not have affected the connection of the [disease] vectors with monkeys in the forest," he added.

Endangered species

According to epidemiological reports of the state Department of Health, 18 municipalities have reported death of monkeys, which are under analysis. Other 70 municipalities heard rumors of death of monkeys. For Sérgio Lucena, these data do not give the dimension to the animals mortality. "Monkeys are dying in large numbers," he reported.

In Lucena's view, the phenomenon emerged in Minas Gerais, but it already spread to Espírito Santo. The situation threatens endangered species, like the native monkey muriqui. However, howler monkeys are the most affected. He also said that studies carried out during the 2009 outbreak in Rio Grande do Sul state showed that populations of howler monkeys were reduced to 20%.

The state Department of Health is concerned about the violence against monkeys, registered in some municipalities. Some people believe that killing the animals can help prevent the disease in humans. The department has wrote a post on its blog to tear down this myth and explain that animals are actually our allies and help map the disease. "Viral infection lasts only three to five days.”

Then monkeys die or become immune. Therefore, this violence is usually committed to healthy animals that have not had contact with the virus or are immunized and pose no risk," added the text.

Translated by Amarílis Anchieta