Oropouche outbreak viruses have been flaring in the Amazon for decades, but historically the pathogen has caused little trouble to the rest of the world. But this seems to be changing. In 2024, the virus shows it can move.
Most of the more than 11,000 cases this year occurred in Brazil and Peru, where the virus has long been known, but it has also been detected in 2024 in Bolivia, Colombia, Ecuador, Guyana, Panama and Cuba—the latter countries reported 603 cases as well as their first domestic transmission. Infected travelers have also transported the virus to North America and Europe: This year, the virus was detected twice in Canada and 94 times in the United States—with 90 cases reported in Florida —while 30 imported cases were detected across Spain, Italy and Germany.
For those who study Oropouche and other arboviruses – a family of viruses transmitted by arthropods such as mosquitoes and ticks – the situation is worrying. 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 there is not complete certainty about the role,” said Juan Carlos Navarro, director of research at SEK International University, where he heads the epidemiology and emerging diseases group. everyone’s role”.
The first symptoms of the disease appear suddenly 3 to 12 days after being bitten and usually last 4 to 6 days. Symptoms include headaches, 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 meninges—may develop. Oropouche infections are generally uncomplicated, although unpleasant, although Brazil recorded two virus-related deaths for the first time this year.
As cases occur, researchers are increasingly discovering something that might explain why the virus emerged and spread: deforestation. Changing natural land for farming, oil drilling or resource extraction “appears to be the main cause of the epidemic,” Navarro said. “It brings together three linkages: virus, vector and human.”
A natural cycle with gaps
In 1955, a young coal burner fell ill after two weeks of work and slept in the woods near the Oropouche River in Trinidad and Tobago. He had a fever for three days. That was the first recorded case of disease caused by the Oropouche virus. Since then, dozens of outbreaks have been reported, most occurring in the Amazon basin.
Navarro has spent 30 years studying arboviruses such as dengue fever, equine encephalitis, Mayaro and, since 2016, Oropouche. It has two transmission cycles. In the jungle, Oropouche virus reservoirs—animals that keep the virus circulating, even when not sick themselves—are thought to be non-human primates such as neotropical marmosets and capuchins, sloths, rodents and birds. Viruses have been isolated from these organisms or antibodies have been found in their bodies. In fact, this disease is also known as “lazy fever”. Navarro said the role sloths and non-human primates play in the disease transmission cycle is not understood. “They may be amplifying the host” — meaning they are potentially allowing the virus to reproduce rapidly in high concentrations in their bodies.
When an epidemic occurs in humans, there will be a second cycle of transmission. In this, humans are the amplifying hosts and the virus is transmitted between them by blood-feeding insects. The main vector that transmits pathogens between people is the mosquito Culicoides paraensis, about the size of the head of a pin and found from Argentina to the United States. Some studies show that Culex and Aedes mosquitoes can also transmit Oropouche disease. In fact, the first virus isolation in Trinidad and Tobago was from Coquillettidia venezuelensis, another type of mosquito.
