What Is Sloth Fever? MDs Explain Oropouche Virus Outbreak

There’s no shortage of illness swirling on a daily basis, but warm weather and travels brings in a slew of insect-borne diseases. From babesiosis to malaria to Lyme disease, it’s always worth protecting yourself from pesky critters. More recently, another less-known virus is making the rounds across the US: sloth fever.

Formally known as Oropouche virus, sloth fever is an insect-borne illness spread through the bite of an infected midge (a type of small fly) or mosquito, says Amesh Adalja, MD, an infectious disease expert and senior scholar at the Johns Hopkins Center for Health Security. It’s been around since the 1950s, but recent outbreaks in Brazil and Cuba have sounded the alarms causing national warnings among travelers, he says.

In fact, the Centers for Disease Control and Prevention (CDC) recently issued a health advisory after 21 Oropouche cases have been reported among US travelers returning from Cuba. Florida currently has the most cases, but there has been at least one in New York.

People who live and/or travel to the affected countries are at the highest risk of getting infected with Oropouche virus, but with cases on the rise, it’s important to know what causes sloth fever in the first place. Ahead, we outline everything you need to know about sloth fever and how to best stay protected.

Experts Featured in This Article:

Amesh Adalja, MD, is an infectious disease expert and senior scholar at the Johns Hopkins Center for Health Security.

What Is Sloth Fever?

Sloth fever, officially known as Oropouche virus, is a viral infection that spreads from the bite of an infected midge or mosquito, Dr. Adalja says. The virus is most commonly found in South America, Central America, and the Caribbean, and causes flu-like symptoms typically lasting between two to seven days, he says. More than 8,000 cases of Oropouche have been reported in Brazil, Bolivia, Peru, Colombia, and Cuba, and travelers returning from the affected countries have reported cases in New York and Florida, Dr. Adalja adds.

What Causes Sloth Fever?

Sloth fever is a virus transmitted to people primarily through the bite of an infected midge or mosquito, says Dr. Adalja. An insect becomes infected by feeding on a person or other animal who has sloth fever, and if that infected insect then bites you, it transmits the virus, causing you to become sick.

According to the CDC, the virus circulates in forested areas between insects and “non-human primates” such as rodents, birds, and sloths, hence the name. From there, infected insects bite humans, who then introduce the virus into urban areas further perpetuating the spread.

Person-to-person transmission has not been documented, so you can’t get sloth fever from being around an infected person (AKA it’s not contagious) — though there is concern that mother to fetus transmission is possible in pregnant people, Dr. Adalja says.

Sloth Fever Symptoms

Sloth fever can be present similarly to other mosquito-borne diseases like dengue fever, Zika, or malaria, and the following symptoms typically occur within three to 10 days of exposure, according to the CDC.

Symptoms typically last two to seven days, but up to 70 percent of infected people report having recurrent symptoms within days to weeks after the resolution of initial illness.

How to Prevent Sloth Fever

The key to preventing sloth fever is to protect yourself against bug bites, especially in areas with high transmission like Brazil and Cuba, Dr. Adalja says. Proper measures include using U.S Environmental Protection Agency (EPA)-approved insect repellent and wearing long sleeves, pants, and socks, per the CDC. Effective window and door screens and insect repellent nets over strollers and beds are also recommended, and it’s best to avoid areas with stagnant water. It can also be beneficial to use a fan when sitting outdoors to help blow insects away.

Additionally, the CDC recommends that pregnant people avoid nonessential travel to areas of high infection, including Brazil and Cuba, to minimize the risk of outbreaks.

Sloth Fever Treatment

There is no vaccine or specific medication for sloth fever, so treatment consists of supportive care that includes hydration, plenty of rest, and fever or pain management, Dr. Adalja says. Most symptoms are typically mild and subside within a week, but if you experience severe or persistent symptoms, visit your doctor immediately for a proper diagnosis.

From there, a healthcare provider will order a blood test to check for sloth fever antibodies and/or rule out additional infections, Dr. Adalja says.

Andi Breitowich is a Chicago-based freelance writer and graduate from Emory University and Northwestern University’s Medill School of Journalism. Her work has appeared in PS, Women’s Health, Cosmopolitan, and elsewhere.