Silent Epidemic: 'Sloth Fever' Infects Millions

New research indicates the Oropouche virus, known as 'sloth fever,' has a far greater reach than official figures suggest. Scientists estimate that approximately 9.4 million people in Latin America and the Caribbean have been infected since 1960. In Brazil alone, around 5.5 million cases are calculated based on mathematical models and historical data.

The Oropouche virus is transmitted by biting midges, which are smaller than mosquitoes and carry the virus between primates and humans. While most infections are mild and resolve within a week, severe complications like neurological disorders, miscarriages, and liver issues can occur in about one in a thousand cases.

Historically confined to the Amazon basin, Oropouche cases have recently been detected in Cuba, Barbados, and Europe, with imported cases also reported in the UK, Italy, Spain, Germany, France, the Netherlands, the US, and Canada in 2024 and 2025. This spread highlights insufficient surveillance methods.

Researchers found that in Manaus, Brazil, an estimated 300,000 people were infected between 2023 and 2024, a figure nearly 260 times higher than confirmed cases. This vast underestimation is attributed to many cases being asymptomatic or mild and going undiagnosed.

Combating Oropouche requires different strategies than mosquito-borne diseases, as the midges thrive in humid, vegetated areas. The virus's ability to spread rapidly across Brazilian states and into neighboring countries underscores the need for enhanced detection systems, particularly outside major urban centers.