People in Brazil are killing dozens of monkeys out of fear they will spread yellow fever, despite the fact that the illness cannot be transmitted between monkeys and humans.

Officials are trying to stop locals in Rio de Janeiro, who are poisoning the monkeys and beating them to death, AFP reported. So far this year, authorities have found more than 200 dead monkeys, almost 70 percent of which were attacked by humans. That represents a significant jump in human-caused monkey deaths from last year, when less than half of the dead had been killed by people.

The violence against the animals comes as yellow fever spreads through the area. According to AFP, a couple dozen people have died already this year from the illness and the government does not have enough vaccine stock to inoculate everyone.

“People should understand that it’s the mosquito transmitting the yellow fever virus,” Rio Veterinary Center coordinator Fabiana Lucena told AFP. “The monkey is a victim and if there are no more monkeys in the countryside, then mosquitoes will come to attack people. … Monkeys serve as sentinels — they show us where the virus has gone.”

Yellow fever is a virus that affects tropical and subtropical areas, according to the U.S. Centers for Disease Control and Prevention. Most people who are infected do not become severely ill. Mild symptoms can include a fever, chills, a headache and other body aches, nausea and weakness while the more serious cases can bring on jaundice, bleeding, shock and organ failure.

The latter infections, which the Mayo Clinic refers to as reaching the “toxic phase,” may also come with a slowed heart rate, seizures, delirium and coma.

The CDC reported that between 20 percent and 50 percent of people who progress to the more severe form of the illness could die.

Symptoms could appear from a few days to a week after infection.

The Mayo Clinic points to the Aedes aegypti mosquito in particular as the culprit behind yellow fever transmissions, spreading the virus to a human or monkey by a bite that allows it to enter the bloodstream.

yellow-fever-vaccine Yellow fever has been spreading through Brazil, but a vaccine can prevent infection from the virus. Photo: MIGUEL SCHINCARIOL/AFP/Getty Images