Uptick in Oropouche 'Sloth' Virus Spurs CDC Health Alert

The mosquito-borne virus, which has caused over 8,000 infections, pregnancy complications, and two deaths, is expanding into South America and the Caribbean.

On August 16, the U.S. Centers for Disease Control and Prevention (CDC) issued a health advisory warning healthcare providers and travelers of an increase in Oropouche virus disease in the Amazon basin and its spread into new areas, including South America and the Caribbean.

So far this year, over 8,000 cases of the disease have been reported in seven countries. The virus is also linked to two deaths in Brazil and five cases of transmission from pregnant women to their unborn babies.

In the United States, the Florida Health Department says that in 2024, 11 travel-related cases of Oropouche virus disease have been reported in Hillsborough, Lee, Miami-Dade, Orange, and Polk counties.

European health authorities have also seen an increase in the disease among Europeans traveling to the affected regions. In June and July, 19 cases occurred among people who visited Cuba and Brazil.

The CDC says that despite the handful of travel-related cases, there is no evidence that midges or mosquitoes in the United States or its territories are transmitting the virus locally. Moreover, European officials report no local transmission of the disease.

What is Oropouche or ‘sloth’ virus disease?

Oropouche, also known as the "sloth virus," is transmitted via biting midges (no-see-ums) and mosquitoes. It's nicknamed the sloth virus because the pale-throated sloth is thought to play a key role in transmission to humans.

The disease has an incubation period of three to 10 days and causes symptoms in around 60% of those infected. Symptoms of Oropouche are similar to Zika, dengue, and chikungunya viruses and include sudden fever, rash, eye pain, muscle aches, and vomiting.

While the symptoms tend to be mild, the virus can cause spinal cord and brain inflammation or bleeding issues in rare cases.

In a Science Media Centre statement, Professor Stephen Graham from the School of Biological Sciences Infection and Immunity at the University of Cambridge said that the outbreak is unusual due to its broad geographic spread.

"It's also very unusual in the fact that we have observed the first recorded cases of mortality from Oropouche virus infection – two women in their 30s with no known co-infections or other serious disease," Graham added. "This marks quite a change in the virus as it has always made people sick, with debilitating fever and muscle pain for about one to two weeks, and occasionally neuronal symptoms like meningitis, but it has never before killed people."

Graham is also concerned about recent cases of vertical transmission.

"We have unfortunately now seen several cases of early-term abortions where the fetus was infected with Oropouche virus," Graham said. "This has potential public health implications, so we need to maintain vigilance and monitor the situation carefully."

According to the CDC, no specific treatments or vaccines are available to combat the Oropouche virus. The Agency says healthcare providers should closely monitor pregnant individuals infected with the disease and their newborns for signs of vertical transmission.

How to prevent Oropouche virus disease

People traveling to areas impacted by the Oropouche virus can help reduce their chances of becoming infected by wearing long-sleeved shirts and pants, using an Environmental Protection Agency (EPA) approved insect repellent, and staying in places with air conditioning and window screens.

Travelers should also protect against no-see-um and mosquito bites for three weeks after they return home to lessen viral spread and reduce the risk of importing the virus into the U.S.

"We have no evidence that the virus can spread directly from person to person – you need an insect to bite you and then bite someone else to transmit the disease," Graham said. "The good news here is that most people recover completely from Oropouche virus infection within a few weeks, so this virus won't cause a SARS-CoV-2-like global pandemic."