March 22 (UPI) -- Yellow fever, a viral disease transmitted by mosquitoes, is spreading through Brazil, infecting and killing both monkeys and humans.
According to the latest reports from local scientists, several thousand monkeys -- most of them howler monkeys -- have been killed by the virus since the outbreak began in late 2016.
Significant portions of the Brazilian rainforest are without a single howler monkey, researchers say.
"It was just silence, a sense of emptiness," Karen Strier, an anthropologist at the University of Wisconsin, said of visiting a familiar patch of forest in the state of Minas Gerais. "It was like the energy was sucked out of the universe."
Strier's patch of forest, like most of what's left of the Amazon, is now a fragment -- protected but isolated, surrounded by agricultural lands. Somehow, yellow fever has spread from patch to patch across large swaths of the rainforest, wiping out significant portions of the resident monkey populations.
"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," Sérgio Lucena Mendes, a professor of animal biology at the Universidade Federal de Espirito Santo, said in a news release. "It is also surprising that it is spreading across such a large geographic region."
The outbreak is affecting humans, too. At least 400 people have been infected, and approximately 220 have died -- most of them in Minas Gerais. Several hundred more reported infections are being investigated.
Officials are worried the virus could spread from rural areas to the coastal cities, like Rio de Janeiro and Sao Paolo. So far, there have been no confirmed cases of the virus being transmitted by Aedes aegypti, the mosquito vector capable of sustaining an urban outbreak.
In recent weeks, millions of people in Brazil's urban centers have been vaccinated against the disease, as health officials scramble to control the outbreak.
Meanwhile, in the jungle, scientists are anxious to observe the ecological consequences of the sudden trauma.
"No one really knows the consequences for the other primates or the forest when nearly the entire population of an abundant species dies from disease in just a few months," Strier said. "We are in a position to learn things we never knew before, with all the background information that we have collected."
Strier, who has worked hard to improve protections for several monkey species, believes the howler population can rebound. In the meantime, other vulnerable species -- like the black capuchin, the buffy-headed marmoset and the critically-endangered northern muriqui -- will have a bit more space and a lot more fruit.