Hundreds of monkeys were found dead in Rio de Janeiro, Brazil, after a recent rise in yellow fever cases. Authorities suspect that about 69 percent of the deaths were due to illegal killings of the primates by humans.

Residents in Rio have falsely assumed that monkeys in the area were helping the spread of yellow fever — a disease that claimed the lives of 25 so far in 2018. 

Fabiana Lucena, who works as coordinator at the Rio Veterinary Center, where the bodies of the monkeys were brought in for autopsy, said the locals were making a huge mistake in fatally attacking the primate population due to their inaccurate notion about yellow fever.

"People should understand that it's the mosquito transmitting the yellow fever virus. The monkey is a victim and if there are no more monkeys in the countryside, then mosquitoes will come to attack people," she told French newspaper AFP. "Monkeys serve as sentinels they show us where the virus has gone.”

Monkey deaths in Rio have already reached 238 this year, while a total of 602 monkeys died in 2017. And about 40 percent of the deaths among primates last year were caused by humans. More than 50 percent of monkeys killed this year appeared to have been beaten to death or poisoned.

“Here, you see multiple fractures to the jaws, cervical area, as well as numerous skull traumas," Lucena said, as she examined a primate's head.

Another factor that raised a red flag was the fact that many of the primates’ bodies were recovered from the city, while their natural habitat is the forest. The situation reached a point where the mayor's office set up a hotline for reporting monkey corpses and the city sanitation service announced they will be launching a campaign against the killings.

“At the time of the first human deaths from yellow fever in mid-January, we’d sometimes get 20 monkeys found dead in a day, with 18 of them showing signs of attack,” Lucena said.

Monkey In this representational image, a veterinarian examines dead monkeys at the Municipal Institute of Veterinary Medicine in Rio de Janeiro, Brazil, Feb. 8, 2018. Photo: Getty Images/ CARL DE SOUZA

Although Rio government has launched a mass vaccination program, it lacked the extensive resources needed to cover lifetime vaccination requirements for its population.

According to Lucena, people might have decided to eliminate what they viewed as the root cause behind yellow fever because of the lack of governmental capabilities in tackling the situation.

"To have a more effective vaccination campaign, we have to identify the zones where monkeys are dying from yellow fever,” she said. “When people kill them, the virus is harder to trace."

Samples recovered from the corpses of the monkeys were also sent to the Osvaldo Cruz research center, at times, to be tested for yellow fever and other diseases. Similar surges in monkey deaths were also observed in Sao Paulo and Minas Gerais states in Brazil — both hit with the worst bouts of yellow fever this year.