Wednesday at #TropMed25, researchers working in Panama and Colombia presented new insights from their investigations into recent outbreaks of oropouche virus in those countries as they seek to understand why this previously obscure pathogen is now emerging as a public health threat in the Americas.  

The disease, transmitted mainly by tiny flies (aka, midges or no-see-ums), was once seen mainly in the Amazon Basin. But it has recently been detected in several countries in the Americas, with outbreaks occurring in Brazil, Colombia, Panama and Cuba. And the flies that can transmit the disease are common in the United States. Oropouche virus can cause a range of symptoms, notably an abrupt onset of fever — which can subside and then recur several weeks later — along with muscle and joint pain. There have been reports, though rare, of infections causing meningitis or encephalitis and investigators are probing potential fetal risks. 

Sandra Lopez-Verges, PhD, with the Gorgas Memorial Institute of Health Studies in Panama, described the discovery of an outbreak in the Darien Gap region of Panama in December 2024 that began with reports of a mysterious illness that resembled chikungunya and dengue but turned out to be infections with oropouche virus. She said that as of July there have been 664 cases in Panama, most of them in the Darien province but also in the adjacent Panama province.  

She said that the virus was known to exist in Panama in animals, and while there have been occasional reports of human infections, the scale of the current outbreak is unprecedented. She said genome sequences taken from patients in the Darien Gap revealed that their infections were caused by a strain of the virus that has never been seen in Panama. It appears to be similar to what is now circulating in Brazil, she said, with an even closer match to oropouche virus samples recently taken from patients in Cuba.  

Lopez-Verges said health officials in Panama now believe the strain currently circulating in Panama may have come into the country via migrant workers traveling from Cuba.  

The outbreak in Panama bears similarities to the 2024 oropouche outbreak in Leticia, Colombia, in that the virus detected in Leticia patients is distinctly different from oropouche that’s been seen previously in Colombia — and the country has never experienced such large outbreaks. Jorge Osorio, DVM, PhD, with the University of Wisconsin’s Global Health Institute, called it a “new lineage” of oropouche that arrived in Colombia from Brazil, possibly via three independent introductions.  

Alexander Ciota, PhD, director of the Arbovirus Laboratory at the New York State Department of Health, said there is growing interest in whether the virus has undergone genetic changes that are making it more transmissible. He pointed to a 2025 study in Scientific Reports that found that the strain involved in recent outbreaks is more transmissible than older strains of the virus. The study authors said their findings should increase concern about the risk of spread within the United States following potential introduction.