Updated | Monkeys in Brazil are being illegally killed for fear that they might help spread yellow fever. Not only is this fear misplaced, experts warn that killing monkeys could hinder efforts to get the vaccine to the most at-risk populations.
So far 238 monkeys were found dead in Rio state since the beginning of 2018, and of these, 69 percent showed evidence that they had been purposely killed by humans, either by beating or poisoning. This is compared to 602 monkeys corpses that were recovered in all of 2017, of which only 40 percent showed evidence of being killed by humans, AFP reported. When humans first began to die from yellow fever in early January, as many as 20 monkeys were found dead in a single day, with 18 showing signs of human attacks.
Related: What You Need To Know About Yellow Fever, The Virus Deadlier Than Zika
As of January 2018, the amount of confirmed yellow fever cases in Brazil tripled in comparison to those of 2017, The World Health Organization reported. The cases are concentrated in São Paulo, and include 20 deaths. On January 25, the World Health Organization issued an alert for potential travelers to Brazil to get a yellow fever vaccination before their trip, CNN reported.
Yellow fever is caused by a virus that is spread through the bite of infected mosquitos. Monkeys also contract the virus through mosquito bites but are unable to pass the virus to humans. Daniel Caplivski, an infectious disease specialist and the Director of the Travel Medicine Program at the Icahn School of Medicine at Mount Sinai, told Newsweek that although monkeys are not able to directly pass the disease to humans, in some cases a mosquito that bites an infected monkey can contract the virus and then pass it to a human. However, Caplivski explained that in most cases, it's mosquitos biting infected humans that causes the virus to spread among human populations. Nonetheless, Caplivski emphasized that killing monkeys would do nothing to quell human outbreaks.
"The short answer is no," said Caplivski. "Basically yellow fever is a virus that is transmitted by mosquitoes."
In addition, epidemiologists use monkeys as a way of tracking where infected mosquitoes dwell. Where there are sick monkeys, there will soon be sick humans, AFP reported.
"Often they [epidemiologists] do look for dead monkeys as a warning sign that yellow fever virus might be present in circulation nearby," said Caplivski. "It is part of the surveillance."
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Yellow fever is a virus found in tropical and subtropical areas. Most individuals with yellow fever do not have any symptoms. If they do display symptoms, they tend to be mild. The most common symptoms include a sudden onset of fever, headache, back pain and general body pain. In addition, individuals may experience nausea and vomiting, general tiredness and overall weakness, the Center for Disease Control and Prevention reported.
Although most who contract yellow fever will recover, about 20-50 percent with severe symptoms may die from the disease.
There are not enough yellow fever vaccines in Brazil to fully vaccinate every citizen. This problem is not unique to Brazil, as according to Caplivski it is related to the economics of global pharmaceuticals. Vaccines for diseases such as yellow fever simply do not make as much money and drug companies will not heavily invest in their production.
"Even in the U.S. we are currently going through a vaccine shortage and travelers are having trouble getting the vaccine," said Caplivski.
In addition, the vaccine is only effective if given at least 10 days before the individual comes in contact with the virus, CNN reported. For this reason, vaccines are usually reserved for the most at-risk populations. Following yellow fever trends in monkey populations allows researchers to predict which human populations are most at risk for disease outbreaks. They are then able to get the vaccines to the individuals who need it the most.
"The monkey is a victim and if there are no more monkeys in the countryside, then mosquitoes will come to attack people," Fabiana Lucena, the coordinator at the Rio Veterinary Center, in Rio de Janeiro, where the bodies of dead monkeys are being collected, told AFP. "Monkeys serve as sentinels—they show us where the virus has gone."
Updated: This article has been updated to include additional information and quotes from Dr. Daniel Caplivski.
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