Oropouche eruptions The virus has been flaring up in the Amazon for decades, but in the past the pathogen has caused little concern in the rest of the world. But that 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 old acquaintance, but it was also found in Bolivia, Colombia, Ecuador, Guyana, Panama and Cuba in 2024 – the latter reported 603 cases, as well as one for the first time Domestic transfer. Infected travelers also carried the virus to North America and Europe: This year it has been found twice in Canada and 94 times in the United States – 90 cases were reported in Florida – while 30 imported cases were found in Spain, Italy and Germany.
For those who study Oropouche and other arboviruses — the family of viruses transmitted by arthropods such as mosquitoes and ticks — the situation is concerning. Although there is evidence of the transmission cycle, there is not enough information to accurately predict Oropouche’s future behavior. “We have some pieces of the puzzle, but there is no complete certainty about what role each plays,” says Juan Carlos Navarro, research director at SEK International University, where he leads the Emerging Diseases and Epidemiology Group.
The first symptoms of the disease appear suddenly three to twelve days after the bite and usually last four to six days. Symptoms include headache, muscle and joint pain, chills, nausea, vomiting and sensitivity to light. Rashes and bleeding from the gums or nose may occur, and in severe cases, meningitis or encephalitis – an inflammation of the brain and its membranes – may develop. Oropouche infection is generally uncomplicated, if unpleasant, although Brazil recorded two deaths linked to the virus for the first time this year.
Where cases have emerged, researchers are increasingly discovering something that could explain why the virus emerges and spreads: deforestation. Conversion of natural land for growing crops, extracting oil or extracting resources “seems to be the main driver of outbreaks,” Navarro says. “It brings together three connections: the virus, the vector and the human.”
A natural cycle with gaps
In 1955, a young charcoal burner fell ill after working and sleeping for two weeks in the forest near the Oropouche River in Trinidad and Tobago. He had a fever for three days. This was the first documented case of Oropouche virus disease. Since then, dozens of outbreaks have been reported, most of which occurred in the Amazon basin.
Navarro has dedicated 30 years to researching arboviruses such as dengue fever, equine encephalitis, Mayaro and, since 2016, Oropouche. There are two transmission cycles. The reservoirs of Oropouche virus – the animals that keep the virus circulating even when they do not become ill themselves – are thought to be non-human primates such as Neotropical marmosets and capuchins, sloths, rodents and birds. The virus was either isolated from these creatures or antibodies were found in their systems. In fact, the disease is also known as “sloth fever.” It is unclear what role sloths and non-human primates play in the transmission cycle, says Navarro. “They are likely amplifying hosts” — meaning they likely allow the virus to reproduce quickly at high levels in their bodies.
In an epidemic among humans, a second cycle of transmission occurs. Humans are the amplifying hosts, and the virus is transmitted between them by blood-feeding insects. The main vector that transmits the pathogen between people is the mosquito Culicoides paraensis, It is the size of a pinhead and is found from Argentina to the United States. Some studies suggest that Culex and Aedes mosquitoes can also transmit Oropouche. In fact, the first isolation of the virus occurred in Trinidad and Tobago Coquillettidia venezuelensis, another type of mosquito.
