Health experts sound alarm over new 'sloth fever' threat lurking in travel hotspots — here's what you need to know

In an effort to raise awareness, several health organizations throughout the world are sending out warnings regarding the emergence of an illness known as "sloth fever."   

What's happening?

Much like the coronavirus, sloth fever, or Oropouche virus, has been around for decades, yet it has managed to fly under the radar in the public eye. 

Now, health officials have begun warning of its dangers, such as in a recent advisory from the Canadian Medical Association Journal — noting outbreaks in warm-weather countries such as Bolivia, Brazil, Peru, and Cuba.

Why is sloth fever important?

Oropouche virus was first identified in 1955 in a 24-year-old forest worker in Vega de Oropouche, Trinidad and Tobago. According to the CDC, Oropouche virus is endemic to the Amazon basin. 

Oropouche virus became known as sloth fever after scientists first investigating the virus found it in a three-toed sloth. Since then, researchers have noted that the virus is transmitted primarily by mosquitoes and biting midges. This is called a vector-borne illness. 

Symptoms of sloth fever include fever, severe headache, chills, muscle aches, and joint pains, though many cases are considered relatively mild. Most symptoms can last between two to seven days. It has also been reported that 60% of those infected with sloth virus symptoms can experience a recurrence of symptoms days or even weeks after the initial infection.   

With increasing average temperatures seen across the globe, vector-borne illnesses have gained a longer window to spread. As the global temperature increases, the spread of infectious illnesses from vectors may increase thanks to more hospitable environments for a longer period of the calendar. 

It may seem small, but extending the mosquito season for even a week can have a significant impact on human health and is one of the simplest reasons to take pollution more seriously. 

In August 2024, the CDC issued an alert to the rise in sloth fever cases. The organization recognized an increased risk to travelers to the Amazon basin, this includes travelers returning to Canada and the United States. 

There have also been "locally acquired" cases reported in Brazil, Bolivia, Peru, Colombia, and Cuba. According to a study in the journal CMAJ, as of March 2025, "local transmission of Oropouche virus in the US has not been found."  

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Despite the increase in concern, the mortality rate of sloth fever still remains very low. In 2024, there were two deaths reported that were linked to sloth fever. However, like most RNA viruses, sloth fever could eventually have the potential to mutate. This could lead to variations that contain a much higher mortality rate, especially to those with underlying medical concerns.  

What's being done about sloth fever?

For now, travel restrictions have not been recommended, though travelers are encouraged to take the proper precautions. The Government of Canada has urged those who are pregnant or planning to become pregnant to discuss the risks of sloth fever with their health care provider.  

In order to avoid transmission of the virus, health experts are promoting the use of personal protection measures such as mosquito nets, insect repellent devices, repellent-treated clothing, and anti-mosquito repellents. While these measures can help prevent midge bites, they are not always 100% effective. 

Until more research is available, there are currently no vaccines to prevent sloth fever or medicines specifically designed to treat symptoms of the virus.  

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