Yellow fever plagues Brazilian monkeys

In accordance with current trends of animal endangerment, the brown howler monkey community has lost thousands of members. The brown howler is a New World monkey native to southeastern Brazil that has recently experienced declines in population due to mortality from yellow fever exposure.

Yellow fever is an infectious disease that affects both humans and nonhuman primates and is transmitted by mosquitoes that feed on infected primates.

The disease is quite prevalent in the tropical and subtropical regions of South America and Africa. In humans, symptoms range from fever to severe liver disease coupled with bleeding.

Since late 2016, a group of brown howler monkeys inhabiting a private, federally-protected reserve has been decimated by a wave of yellow fever. This is alarming, especially considering the fact that such a drastic drop in monkey population from disease is unprecedented.

The Feliciano Miguel Abdala Private Natural Heritage Reserve which houses these monkeys is four square miles of green, landlocked by agricultural and pasture lands. The isolation of the reserve brings into question the method by which the yellow fever reached the piece of land.

“It was just silence, a sense of emptiness. It was like the energy was sucked out of the universe,” Karen Strier, an anthropological professor at the University of Wisconsin-Madison, said upon her visit to the reserve in January 2017.

Strier leads a team of scientists that include Sérgio Lucena Mendes, an animal biology professor at the Universidade Federal de Espírito Santo, and Carla Possamai, a former postdoctoral researcher at the same university. Together, they plan to census the remaining monkeys at the reserve and analyze the data in comparison to previously conducted censuses.

Additionally, the team wants to study the way in which the remaining monkeys deal with the aftermath of the yellow fever wave, particularly the regrouping and restructuring of a society.

“I am very surprised at the speed with which the outbreak is advancing through the landscape and by how the virus can jump from one patch of forest to another, even if they are hundreds of meters apart. It is also surprising that it is spreading across such a large geographic region,” Mendes said in a press release.

But yellow fever has not only been affecting the brown howler monkeys. As of mid-March, Brazilian health officials had confirmed 150 human deaths among 400 cases of the disease. An additional 900 cases are yet to be confirmed, and there is mounting concern over the disease’s spread to cities. For now, the disease is fairly localized, with most cases taking place within Minas Gerais, the state where the brown howler monkey reserve is located.

Efforts to provide protection to the monkeys have begun with educating the public about the monkeys’ role in warning humans about the presence of a pathogen.

At the moment, there are not many estimates regarding the future of the brown howler monkeys, but Strier’s experience with the critically-endangered muriqui monkey has validated the possibility that decimated populations might recover under much protection.

Despite the effects of yellow fever on the brown howler monkeys, their partial elimination allows Strier to study the behavior of the muriqui monkeys in the absence of their main competitors. Thus, although the decline in population may be a grim discovery, it simultaneously paves the way for new discoveries to be made.