Oropouche Virus Outbreak: First Deaths and Growing Concerns

An outbreak of the Oropouche virus, also known as sloth fever, is raising concern in South America following the first reported human deaths linked to the disease in Brazil. There are also growing reports of stillbirths and birth defects associated with infections during pregnancy. The virus is primarily transmitted through the bites of infected midges, although some mosquitoes can carry it as well.

The Oropouche virus was first identified in Trinidad and Tobago in 1955, named after the Oropouche River where it was discovered. Since then, it has circulated in Latin America and the Caribbean, with sporadic outbreaks in countries such as Brazil and Peru.

According to the Centers for Disease Control and Prevention (CDC), about 60% of those infected with the Oropouche virus exhibit symptoms, which can include fever, severe headache, joint and muscle pain, nausea, dizziness, chills, and sensitivity to light. These symptoms typically appear three to ten days after infection.

Most people recover within a few days to a month, with symptoms usually lasting less than a week. However, symptoms may recur days or even weeks later. A small percentage of people—fewer than 5%—may develop more severe conditions, including meningitis, brain inflammation, and bleeding, though death is rare.

Currently, there are no specific medications or vaccines for treating or preventing Oropouche virus infection. Health experts recommend preventive measures such as using insect repellents and installing door and window screens to avoid bites from midges and mosquitoes in areas where the virus is known to occur.

The Oropouche virus is sometimes referred to as “sloth virus” or “sloth fever” because it is found in regions inhabited by sloths, although sloths do not transmit the virus themselves. Researchers believe the virus has a reservoir in pale-throated sloths, non-human primates, and some bird species, which may help spread the virus through midges or mosquitoes.

While the Oropouche virus is endemic in parts of South America, making infections and outbreaks not unusual, the current situation is alarming for several reasons. This outbreak appears to be larger and more sustained than typical Oropouche outbreaks, with over 8,000 cases confirmed by laboratory testing this year alone. It is also geographically more widespread than previous outbreaks, affecting areas as far north as Cuba and south as São Paulo in Brazil. The CDC notes that the outbreak is occurring in both endemic regions and “new areas outside the Amazon basin,” where the virus is not usually found.

Brazil has been heavily impacted, with Bolivia, Peru, Colombia, and Cuba reporting locally acquired infections. Several other countries, including the United States, Spain, Italy, and Germany, have reported cases linked to travel, though there is no evidence yet that the virus has established a foothold outside its endemic regions. The outbreak is particularly concerning due to the first reports of fatalities from the virus among two otherwise healthy, non-pregnant women in Brazil. There are also growing concerns about the virus’s potential to spread from mother to fetus during pregnancy, with ongoing investigations into its role in stillbirths, miscarriages, or birth defects.

Despite the Oropouche virus not being new, much remains unknown about it. The Lancet medical journal recently described it as a “mysterious threat” in an editorial. Scientists are uncertain about the factors triggering the current outbreak, although there are theories. The Oropouche virus is an RNA virus with a segmented genome, allowing it to undergo rapid mutations and genetic mixing—a process known as “reassortment.” This can occur if an individual is infected with multiple strains of the virus, potentially leading to a more transmissible or pathogenic variant. Evidence suggests that such genetic changes may have contributed to the current outbreak in Brazil.

The initial symptoms of the Oropouche virus can resemble those of dengue, chikungunya, Zika, or malaria, which can lead to misdiagnosis or delayed identification. According to Stephen Graham, a virology professor at the University of Cambridge, the characteristics of the Oropouche virus make it unlikely to cause a global pandemic like COVID-19. “The good news here is that most people recover completely from Oropouche virus infection within a few weeks, so this virus won’t cause a SARS-CoV-2-like global pandemic,” he said. Since the discovery of the Oropouche virus, approximately 500,000 cases have been recorded, according to The Lancet.