outbreak of Oropouche The virus has been raging in the Amazon for decades, but historically the virus has been of little concern to the rest of the world. But this seems to be changing. In 2024, the virus showed that it can travel.
Most of this year’s 11,000-plus cases occurred in Brazil and Peru, where the virus is an adult, but it was also detected in 2024 in Bolivia, Colombia, Ecuador, Guyana, Panama and Cuba – these reported 603 cases as well as country transmission for the first time . Infected travelers have also transported the virus to North America and Europe: This year it was found twice in Canada and 94 times in the United States – with 90 cases reported in Florida – while 30 imported cases were found across Spain, Italy and Germany.
For those studying Oropouche and other arboviruses—a family of viruses spread by arthropods such as mosquitoes and ticks—this situation is troubling. Despite having clues about its transmission cycle, there is not enough information to accurately predict the future behavior of Oropouche. “We have pieces of the puzzle, but we are not completely sure what role each person plays,” said Juan Carlos Navarro, director of research at SEK International University, where he heads the group of emerging diseases and epidemiology.
The first symptoms of the disease appear suddenly between three and 12 days after the bite, and usually last between four and six days. Symptoms include headache, muscle and joint pain, chills, nausea, vomiting, and sensitivity to light. Skin rashes and bleeding from the gums or nose may occur, and in severe cases, meningitis or encephalitis—inflammation of the brain and its lining—may develop. Oropouche infections are usually mild, if not unpleasant, although for the first time this year Brazil has recorded two deaths linked to the virus.
Where conditions have occurred, researchers are increasingly finding something that may explain why the virus appears and spreads: deforestation. Changing the natural environment to plant crops, drill for oil, or mine for resources “seems to be the main cause of disease outbreaks,” Navarro said. “It includes three links: virus, vector, and people.”
A Spaced Natural Cycle
In 1955, a young charcoal burner fell ill after spending two weeks working and sleeping in the forest near the Oropouche River in Trinidad and Tobago. He had a fever for three days. That was the first documented case of Oropouche virus disease. Since then, numerous outbreaks have been reported, most in the Amazon region.
Navarro has devoted 30 years to the study of arboviruses such as dengue, equine encephalitis, Mayaro, and, as of 2016, Oropouche. It has two transmission cycles. In the wild, the sources of the Oropouche virus—animals that keep the virus circulating, even if they themselves are not sick—are believed to be non-neotropical marmosets and capuchin monkeys, sloths, rats and birds. The virus may have been isolated from these organisms or antibodies found in their systems. In fact, this disease is also known as “sloth fever.” It’s unclear what role sloths and great apes play in the transmission cycle, Navarro said. “Maybe they’re growing the hosts”—meaning they’re allowing the virus to replicate more and more in their bodies.
If there is an epidemic among people, there is a second round of transmission. In this case, humans are amplifying hosts, and the virus is transmitted between them by blood-sucking insects. The main vector that transmits the pathogen between humans is the midge Culicoides paraensis, about the size of a pinhead and is found from Argentina to the United States. Some research suggests that Culex and Aedes mosquitoes can also transmit Oropouche. In fact, the first isolation of the virus in Trinidad and Tobago was from Coquillettidia venezuelensis, another type of mosquito.
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