Oropouche virus disease was a relatively rare illness for decades, lurking on the margins of tropical rainforests in the Caribbean and South America.

Sporadic reports of an infection causing fevers, coughs, chills, and body aches emerged among people living near or moving into the jungle. A tiny insect called a midge spreads the disease, and the earliest known case dates back to 1955 in a forest worker near a village called Vega de Oropouche in Trinidad. Since most people who were infected with the virus recovered on their own and since cases were so infrequent, it barely registered as a public health concern.

But a few years ago, something changed.

A major Oropouche fever outbreak beginning in 2023 infected at least 23,000 people across Bolivia, Brazil, Colombia, Cuba, the Dominican Republic, and Peru. It wasn’t just confined to remote wilderness areas but was spreading in metropolises like Rio de Janeiro. In some cases, travelers were infected and then brought the virus home: So far, Oropouche fever has sprung up in the US, Canada, and Europe in people returning from the afflicted region. The outbreak has killed at least five people.

The sudden rise of Oropouche disease startled scientists and health officials. Since its discovery, there have only been around 500,000 known cases. By contrast, there are upwards of 400 million dengue infections each year. It’s likely then that many more Oropouche infections have gone undetected, especially since its symptoms overlap with those from other diseases and there’s little active screening for the virus.

What you’ll learn from this story

• What Oropouche fever is, how you can identify is and what spreads the disease.
• What researchers know about the startling outbreak across South American in 2023 and 2024.
• The threat the disease’s spread poses to the United States.

Now, researchers are looking back at the outbreak to try to find out what they missed and what lessons they can apply to get ahead of future epidemics. Oropouche virus is a critical case study in the complicated factors that drive vector-borne diseases. Dynamics like deforestation, urban sprawl, international travel, and gaps in surveillance are converging to drive up the dangers from infections spread by animals.

And as the climate changes, new regions are becoming more hospitable to the blood suckers that spread these diseases, increasing the chances of these seemingly-remote infections making it to the US and getting established. That means more people will face threats from illnesses that they may never have considered before.

“It’s very likely that these public health problems that people before called ‘tropical disease’ are not so tropical anymore and are basically everywhere,” said William de Souza, who studies arboviruses — viruses spread by arthropods like insects — at the University of Kentucky. “Vector-borne disease is not a local problem; this is a global problem.”

The rising specter of Oropouche fever comes at a time when the United States is cutting funding for research at universities, pulling back from studying vector-borne disease threats, and ending collaborations with other countries to limit their risk.

The Oropouche virus is a classic case study in how humans worsen vector-borne disease

The Oropouche virus belongs to the family of bunyaviruses. They appear as spheres under a microscope, and they encode their genomes in RNA, rather than DNA as human cells do. RNA viruses tend to have high mutation rates, making it harder to target them with vaccines and increasing the odds of reinfection.........

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