Ever since the first yellow fever epidemic was recorded in the Yucatán Peninsula in 1648, this mosquito-borne illness has ravaged communities around the world in various outbreaks. This virus causes severe fever, muscle pain, and severe bleeding in the liver that can lead to death. Yellow fever can also spread between humans and monkeys via mosquito transmission, which is probably how it was first passed to humans.
A current yellow fever outbreak in parts of Brazil is threatening to wipe out several populations of howler monkeys in that country. Thousands of these monkeys, known for their loud calls, have died already, with no sign of the epidemic slowing down. Large areas of protected rainforest areas, that used to resonate with the sounds of the brown howler monkey, have fallen silent.
Unlike past yellow fever epidemics in monkey populations, this one was probably not introduced by other monkeys. In fact, humans may be the culprits. Humans can become infected with the disease without showing symptoms. If they then travel to another area, and are then bitten by a mosquito, the mosquitos can pass the disease to monkeys nearby who have no natural immunity to the illness and who cannot be vaccinated against it. Humans can also carry contaminated mosquitos into the forests in their cars and luggage.
Though the decimation of this species is heart-breaking, there are other reasons to be concerned about this outbreak. First, it is spreading rapidly. It is jumping from one population of monkeys to another, leaving a path of devastation in its wake. Scientists have never seen an outbreak of the disease spread so far and so quickly. This could cause multiple and widespread groups of monkeys to be eliminated, which could have severe ecological repercussions for the rainforest.
This outbreak has also caused an epidemic among humans, the worst of its kind in decades. Officially, there have been over 320 human cases of yellow fever this year, and at least 220 deaths. There may be even more cases that have gone unreported in more remote areas. Authorities have been scrambling to vaccinate as many people as possible against the illness, and millions have already received the vaccine. A major concern for scientists and environmentalists is that people will wrongfully blame the monkeys for the disease, and will end up killing even more of them in an attempt to stop the spread of it.
Even with the loss of so many howler monkeys, many scientists believe the species can rebound after this epidemic. They are more concerned that it may spread to several threatened and endangered money species in the area, such as the black capuchin and the northern muriqui. Researchers are keeping a close eye on the epidemic to try to protect all of these monkeys. They also hope to learn about the spread of the disease so they can try to prevent, or lessen the impact of, future outbreaks.