A little-known disease spread by insect bites has turned deadly, and health officials are sounding the alarm. More than 8,000 cases of Oropouche virus have been reported this year as of August 1. Most have been in South America, but infections are also spreading in countries where it hasn’t been seen before, and dozens of travel-related cases have been reported in the United States and Europe.
The Pan American Health Organization, a regional arm of the World Health Organization, has issued an epidemiological alert for Oropouche virus and raised the public health risk level to “high” for the Americas region.
“Although the disease has historically been described as mild, the geographic spread in transmission and the detection of more severe cases underscore the need for increased surveillance and characterization of possible more severe manifestations,” the agency said in a statement.
Here’s what to know about the emerging threat.
Oropouche Virus: Symptoms and Transmission
Oropouche virus gets its name from the village in Trinidad and Tobago where it was discovered in 1955. Since then, about 500,000 cases have been recorded. But knowledge of the disease is limited, with The Lancet medical journal even calling it a “mysterious threat” in a recent editorial.
About 60% of people who are infected develop symptoms, according to the CDC. These can appear similarly to those caused by dengue or Zika, including sudden onset of fever, chills, headache, muscle pain and joint stiffness. Other symptoms can include eye pain, light sensitivity, nausea, vomiting, diarrhea, fatigue and rash. In rare cases, the disease can infect the nervous system and cause meningitis and encephalitis.
It is endemic to the Amazon basin region of South America, particularly in forested areas where transmission is maintained in a cycle between insects and other hosts such as rodents, sloths and birds. It’s sometimes called “sloth fever.”
People who visit these areas can be bitten by an infected insect and carry the disease back to more urban areas.
Climate change and deforestation create more opportunities for people to interact with infected insects and the raise the risk of spread, according the Pan American Health Organization.
Global Spread and Concerns
The current outbreak is spreading rapidly in countries where the virus is known to circulate and in new places. Locally acquired cases have been reported in Bolivia, Brazil, Colombia, Cuba and Peru. There is no evidence of local transmission in the United States, but several cases have been reported in people who have traveled to places where it is spreading.
The current risk of sustained local transmission in the continental United States is believed to be low, said Dr. Erin Staples, a medical epidemiologist with the CDC’s Division of Vector-Borne Diseases. But the risk level is more uncertain in places like Puerto Rico and the US Virgin Islands that could have similar ecologies to Cuba, she said.
Shifts in the geography of the virus spread suggest that there may be new vectors involved in the cycle, experts say.
This year also marks the first time that there have been deaths reported from Oropouche virus and evidence that the disease can be transmitted from a pregnant woman to her fetus and cause adverse birth outcomes.
Earlier this year, Brazil reported deaths in two young women who were otherwise healthy and not pregnant. A third fatal case in a middle-age man is under investigation, according to the Pan American Health Organization.
There have also been at least five cases in pregnant people that have led to fetal death or congenital abnormalities including microcephaly, a rare birth defect that results in an underdeveloped brain.
Some of these severe outcomes may be the result of more virus circulating, Staples said.
“As we see more people becoming infected, we can see rare and unusual occurrences of clinical symptoms or death,” she said. “But these are all things that CDC is currently working with our partners to learn more about.”
Prevention and Treatment
There is no vaccine to protect against Oropouche virus, and there are no specific antiviral treatments available. Cases can be confirmed through laboratory testing, but it is not available at commercial diagnostic laboratories, and more common viruses like dengue often have to be ruled out first.
“This is a good time to think about mosquito bite prevention: Avoid going out at dawn and dusk, when mosquitoes are most likely to be biting; dress appropriately to protect your skin from bites from mosquitoes and other insects, and to use a mosquito repellent that is effective at preventing infections,” Hamilton said.
The CDC has issued two travel advisories, one encouraging travelers to South America to take “usual precautions” and another suggesting that travelers to Cuba take “enhanced precautions” in protecting themselves from bug bites and seeking medical care when necessary.
And pregnant women should take special precautions, experts say; the CDC recommends that pregnant people reconsider nonessential travel to Cuba.
Understanding Oropouche Virus: A New Threat Emerges
CDC medical entomologist Roxanne Connelly was advising a research fellow who wanted to study an obscure virus usually found in the Amazon region of South America.
“It is not a pathogen that had been in the U.S. before,” Connelly says. But the research fellow wanted to find out which insects found in the United States would be most likely to carry the virus if it spread beyond its usual range.
The virus was Oropouche, which is now making headlines due to an outbreak in Cuba, a handful of cases in travelers from the United States and Europe, and reports of possible stillbirths and birth defects in Brazil. A paper detailing the results was published in 2021—“And now, suddenly, that paper is very important,” Connelly says.
People can get infected with Oropouche virus through insect bites. The virus is spread mostly by tiny biting midges, sometimes called “no-see-ums,” though some mosquitoes can spread it as well. Oropouche infection can cause fever, joint pain, and body aches that usually get better within a week. But for some people, symptoms may come back a few days or up to a few weeks after initially getting better—and for others, the illness can be more severe.
The current outbreak has raised concerns that Oropouche could spread to the United States. A biting midge species that could carry the virus lives in the eastern United States. The study Connelly participated in found that another species usually found in western states could also carry Oropouche.
Connelly is a former University of Florida professor who frequently advised local governments in the state on how to control mosquito populations. But there’s less known about controlling biting midges in the community. Because of their small size, biting midges can crawl through most screens that otherwise keep out mosquitoes. Chemicals used to spray for mosquitoes in the community will also kill biting midges, but those are typically used when mosquitoes are most active. Biting midges can be out and around at different times of day, the time varies among different species, Connelly says.
“We know the equipment and products used to control mosquitoes will also work on biting midges,” she says. “But what’s not been evaluated is how effective the products are in getting to where the biting midges are.” CDC hopes to work with partner agencies to answer that question and conduct more tests on insects collected in the wild, Connelly says.
But the good news is that some of the same prevention tips that prevent other diseases spread by bug bites will help prevent midges from biting as well. If you're going to be outside in an area where biting midges are active:
- Wear light-colored clothing, as biting midges are more attracted to dark colors.
- Use a mosquito repellent that contains DEET, picaridin, or oil of lemon eucalyptus.
- Stay indoors at dawn and dusk when biting midges are most active.
- Use screens on windows and doors to keep biting midges out of your home.
CDC is working to learn more about the potential risks of Oropouche and will keep the public informed and update its recommendations as needed.
