This tropical virus is spreading from the Amazon to the US and Europe

hearths of Oropouche the virus has been raging in the Amazon for decades, but historically the pathogen has been of little concern to the rest of the world. But that seems to be changing. In 2024 the virus has shown it can travel.

Most of this year’s more than 11,000 cases are in Brazil and Peru, where the virus is long known but was also discovered in 2024. in Bolivia, Colombia, Ecuador, Guyana, Panama and Cuba – the latter reporting 603 cases as well as transmission in the country for the first time. Infected travelers also carry the virus to North America and Europe: this year it has been detected twice in Canada and 94 times in the United States – with 90 cases reported in Florida – while 30 imported cases were found in Spain, Italy and Germany.

For those studying Oropouche and other arboviruses — the family of viruses transmitted by arthropods such as mosquitoes and ticks — the situation is alarming. Although there are clues about its transmission cycle, there is not enough information to accurately predict Oropouche’s future behavior. “We have some pieces of the puzzle, but it’s not entirely certain what role each one plays,” said Juan Carlos Navarro, director of research at SEK International University, where he leads the Emerging Diseases and Epidemiology group.

The first symptoms of the disease appear suddenly between three and 12 days after a 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 membranes – may develop. Oropouche infection is usually uncomplicated, albeit unpleasant, although for the first time this year Brazil recorded two deaths related to the virus.

Where there are cases, researchers are increasingly finding something that may explain why the virus appears and spreads: deforestation. Alteration of natural land to grow crops, drill for oil or extract resources “seems to be the main driver of outbreaks,” Navarro says. “It brings together three links: the virus, the vector and the people.”

A natural cycle with gaps

In 1955 a young coal miner fell ill after spending two weeks working and sleeping in the forest near the Oropuche 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 them in the Amazon basin.

Navarro has devoted 30 years to the study of arboviruses such as dengue, equine encephalitis, Mayaro, and since 2016. Oropouche. There are two transmission cycles. In the jungle, the reservoirs of the Oropouche virus — the animals that keep the virus circulating even if they don’t get sick themselves — are thought to be non-human primates such as Neotropical marmosets and capuchins, sloths, rodents and birds. The virus has either been isolated from these creatures or antibodies have been found in their systems. In fact, the disease is also known as “sloth fever”. It’s not understood what role sloths and nonhuman primates play in the transmission cycle, Navarro says. “They probably amplify the hosts” — meaning they probably allow the virus to rapidly replicate to high concentrations in their bodies.

When there is an epidemic among humans, there is a second cycle of transmission. In this, humans are the breeding 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, which is about the size of a pinhead and is found from Argentina to the United States. Some studies have shown 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 kind of mosquito.