What is ‘sloth fever’? The virus’ symptoms and why it’s concerning

A potentially deadly virus known as “sloth fever” has US officials on alert after Florida reported 20 travel-related cases, including nine last week.

Oropouche virus is spread through the bites of infected small flies and mosquitoes. It’s common in parts of South America, though Florida noted that its 20 cases — the first in the US — stemmed from Cuba travel. The virus has also been detected in Europe.

Infection can cause a headache, joint stiffness, pain, nausea and even death in a couple of rare cases. It’s particularly problematic for pregnant women.

Here’s everything you need to know about this emerging threat.

What is ‘sloth fever’?

Oropouche virus (pronounced o-ro-push) is transmitted via midge and mosquito bites to animals and humans, making it an arbovirus. The disease is known colloquially as “sloth fever,” as those slow-moving, bone-breaking mammals are among the animals regularly infected.

The first virus case was recorded in 1955 in a village near the Oropouche River in the Amazon River Basin. During outbreaks, humans carrying the virus are fed upon by insects, who then infect other people.

According to the Lancet Infectious Diseases journal, there have been around 500,000 recorded cases since the disease was first identified. The virus has circulated in Latin America and the Caribbean, with sporadic outbreaks in Brazil and Peru.

From January to the start of August, more than 8,000 “sloth fever” cases have been reported. There were 832 recorded in 2023.

Of these 8,000 cases, two deaths were recorded in Brazil in July. A few instances of transmission from mother to fetus have also occurred, resulting in fetal death or birth defects.

What are ‘sloth fever’ symptoms?

The incubation period for sloth fever is three to 10 days. Symptoms usually begin with a sudden fever and a severe headache, similar to those associated with dengue, chikungunya, Zika viruses or malaria.

Symptoms usually last less than a week, but some patients experience weakness for up to one month.

Around 60% of those infected develop symptoms, which include:

• Headache
• Chills
• Nausea
• Fever
• Maculopapular rash
• Muscle soreness
• Eye pain
• Joint pain
• Vomiting
• Diarrhea
• Fatigue
• Abdominal pain

Severe symptoms

In up to 4% of patients, infection can cause neuroinvasive diseases like meningitis and encephalitis.

Symptoms of neuroinvasive complications include eye pain, confusion, weakness, light sensitivity, neck stiffness and involuntary eye movement.

Sloth fever prevention

The best defense is bite prevention via insect repellent and window and door screens.

There are no vaccines to prevent Oropouche infection. The CDC recommends that pregnant people reconsider nonessential travel to areas of infection, like Cuba.

How is sloth fever treated?

There are no medications that specifically treat Oropouche virus.

Per the CDC, rest, fluids and over-the-counter pain relievers can address symptoms. To reduce the risk of hemorrhage, aspirin and other nonsteroidal anti-inflammatory drugs should be avoided.

Patients who experience severe symptoms should seek immediate medical treatment.