Oropouche virus, a relatively unknown pathogen endemic to the Amazon region, is being tracked by public health officials. It has recently shown unusual activity, spreading to new areas in Central and South America. In the first eight months of 2024, there have been more than 8,000 confirmed infections across Brazil, Bolivia, Colombia, Cuba and Peru.
The United States does not currently have local transmission of Oropouche, but the Centers for Disease Control and Prevention has reported that U.S. travelers returning from active areas have tested positive for the virus. Europe also saw its first cases of Oropouche virus disease in the summer of 2024. As of Sept. 17, the CDC is reporting 74 imported cases of Oropouche disease, with one person exhibiting neuroinvasive disease. Five states and territories have reported these travel-associated cases, with Florida reporting 70 cases.
Maureen Long, D.V.M., Ph.D., associate director for research resources at the University of Florida Emerging Pathogens Institute and professor emeritus in the UF College of Veterinary Medicine, answers some common questions about Oropouche virus.
Q: What is Oropouche virus?
Oropouche is an RNA virus that causes Oropouche fever or disease in people. It belongs to the genus Orthobunyavirus, a group that is unique because the viral RNA is composed of three separate segments. This means when different Orthobunyavirus variants combine, in the case of co-infection, they are likely to develop new strains. Orthobunyavirus are also classically transmitted by arthropod vectors: organisms like mosquitoes, ticks and biting midges that bite livestock and people. Viruses in this genus cause fever and encephalitis in humans, as well as congenital infection and fetal loss in livestock.
Oropouche virus is also called “sloth fever,” because the virus naturally lives in sloths as well as primates and birds.
Q: How does Oropouche virus spread?
Oropouche virus is transmitted by insects in the genus Culicoides, commonly known as biting midges or no-see-ums. These are the little aggravating insects that buzz around your head and get in your mouth and eyes. Biting midges also breed in swampy water. Since Hurricane Debby, their activity has been very high locally due to standing water and high amounts of rainfall.
There is evidence that Culex mosquitoes may transmit Oropouche virus to humans, but they are not as efficient as the midges. Research is ongoing to determine the importance of mosquito transmission.
Q: What are the symptoms of Oropouche fever or “sloth fever”?
The most common symptoms are fever, chills, and headaches, plus muscle and joint aches, a bumpy rash, and light sensitivity. This virus also causes gastrointestinal symptoms, including vomiting and diarrhea, which occur more commonly than in other vector-borne viruses. The good news about the Oropouche virus is that the infection usually is not severe, and people recover in about six to nine days.
In a small number of cases, it can also cause bleeding abnormalities similar to those seen with dengue virus. Oropouche can also invade the brain and spinal cord causing encephalitis and meningitis — inflammation of the brain or tissues surrounding the brain and spinal cord, respectively.
One of the most concerning manifestations described in the current outbreak is that, like Zika virus, there’s evidence that if Oropouche virus infects a pregnant woman, it can then infect the fetus and cause congenital or developmental abnormalities.
Q: Who is at risk of catching Oropouche virus? Who is likely to have a bad outcome if they become infected?
There are two natural history cycles. One is the urban cycle where the virus, facilitated by a vector, moves between people: person — midge — person. The second is the sylvatic cycle, which occurs in nature where reservoir hosts like sloths, primates and birds transmit the virus to the midge and then to people.
For the current outbreak, the urban cycle is the primary mode of transmission. Thus, urban areas where there are dense human populations are of more concern, because there are more opportunities for infected midges to infect other humans.
Interestingly, this disease has a very low mortality rate. In fact, out of about 8,000 recent cases in the Americas, there have only been two deaths. That’s the good news. But those with cardiovascular disease and hypertension have increased susceptibility to the disease, have more severe illness and are likely at a higher risk for mortality. And, of course, there is risk for infection in a developing fetus.
Q: How do you treat Oropouche virus?
There is no treatment, unfortunately. The good news is that since most illnesses are mild, there is not a lot of intervention needed.
Q: What can people do to avoid getting Oropouche virus disease?
In the U.S., the threat is very low. The biggest risk to the U.S. population comes from travel and importation of the virus by an infected person. In these situations, the CDC and vector control personnel are working to make sure Oropouche virus does not become established in subtropical environments such as Florida or areas like Miami, where there’s heavy midge activity, lots of international travel and a high human population.
On a personal level, people should think about repelling midges. Like mosquitos, they are most active in the early morning and evening. On cloudy days right before a storm, when it’s really warm and humid, activity may be intense throughout the day.
Mosquito repellents such as DEET are most commonly used, but products containing picaridin may be a good alternative for people who are sensitive to DEET. Strong fans that move a lot of air to keep the bugs away are also important. Environmental control includes the same things we do to keep away mosquitoes, like getting rid of standing water and cleaning debris. Once a week, clean out plant pots and anything that can carry water, even in the slightest amount. Unfortunately, midges are small enough to get through screens on porches, but they do still help.
Q: Any closing thoughts?
I think people need to be vigilant, but not panic about Oropouche virus. I think pregnant women need to be aware of which countries have active disease, and this information can be obtained from the CDC website, as well as county public health departments. It is also important for pregnant women to visit with their doctor regarding overall risks. For those arriving from counties with ongoing Oropouche disease, the CDC recommends using measures to prevent midge and mosquito bites while traveling and for at least three weeks after arriving in the U.S. More information regarding travel can be obtained from the CDC website.
Written by: Jiayu Liang