Cases of sloth fever, also known as oropouche virus, have risen in August throughout the USA. Nine cases of the Zika-like virus have been reported by Florida’s health department this month, and one case has been reported in New York. As infections continue to rise in the United States, as well as Europe, Latin America, and South America, multiple agencies around the world like the Centers for Disease Control (CDC), Pan American Health Organization (PAHO), and European Centre for Disease Prevention and Control (ECDC) have warned travelers of the disease. Here’s what we know so far about sloth fever, its symptoms, and means of prevention.
What is the sloth fever virus, and how does it spread?
Sloth fever is a colloquial term for the Oropouche virus and is named after the sloth because it carries the virus, though it is spread through insect bites from mosquitos and midges, not through direct contact with the animal.
The disease is also called Oropouche fever, named after the first area where it was discovered in 1955 by the Oropouche River in Trinidad and Tobogo. Today, the virus is endemic to South and Central America, particularly the Amazon basin. Despite it being called “sloth fever,” the virus is also transmitted among primates, birds, and marsupials.
As for its spread in the US, an August report by the Florida’s health department says that it has identified “20 travel-associated Oropouche fever cases” in 2024. The ECDC, in a August 9 report, said that there were 19 imported cases of the virus in June and July 2024, with confirmed infections in Spain, Italy, and Germany. 18 of those cases had a travel history to Cuba and Brazil. As such, it stated that the likelihood of infection for citizens travelling to South and Central America to be “moderate.” Since the virus doesn’t spread between people, like COVID-19, the ECDC also says that catching locally in Europe is “very unlikely.”
The CDC states that more than 8,000 cases of the Oropouche virus disease were reported in the region, including two deaths, between January 1 and August 1, 2024. This is a significant increase from the 832 cases confirmed in 2023.
What are the symptoms of sloth fever?
General symptoms of sloth fever include nausea, dizziness, light sensitivity, fever, chills, muscle pain, headache, and vomiting. 60% of people infected with the Oropouche virus will experience these symptoms, according to the CDC.
However, more severe symptoms are experienced by 5% of patients or less and include neuroinvasive disease symptoms like confusion, intense occipital pain, bleeding, and inflammation in the spinal cord and brain.
It takes somewhere between 3 and 10 days for symptoms of sloth fever to appear, though it can be difficult to identify since the symptoms are similar to those of other viruses like Zika, dengue, and chikungunya. Typically, symptoms last around a week, though they can recur days or weeks later.
Unfortunately, there are no vaccines or medicines that are able to treat the Oropouche virus. As such, the ECDC recommends personal protective measures to reduce the risk of infection. This includes the use of insect repellants, wearing long-sleeved shirts and long trousers, and mosquito bed nets with insecticide-treated mesh. It is recommended that rooms for resting are air-conditioned and are adequately screened with windows and fine-mesh barriers.
Given five cases of transmission in Brazil associated with fetal death and birth defects, multiple health agencies recommend that pregnant women avoid travelling to potential areas of infection.
Despite the virus being known for over half a decade, there is still “very limited knowledge of the disease,” according to an August editorial in Lancet. One potential reason for the current outbreak of the disease is that the virus is composed of three RNA segments instead of one, leading to higher rates of mutations.
