Topline
An outbreak of Oropouche virus, a little known and potentially dangerous disease also named sloth fever, is spreading in South America, concerning scientists after the first human deaths from the virus were reported in Brazil and growing reports of stillbirths and birth defects from infections during pregnancy.
There is an outbreak of sloth fever in South America.
Key Facts
Oropouche virus is primarily spread through the bites of infected midges, though some mosquitoes have been known to carry the virus.
It was first discovered in Trinidad and Tobago in 1955 on the Oropouche river that it was named after and the virus has circulated in Latin America and the Caribbean since, with sporadic outbreaks recorded in countries like Brazil and Peru.
Around 60% of people infected with the virus will display symptoms, according to the Centers for Disease Control and Prevention, which can include fever, severe headache, joint and muscle pain, nausea, dizziness, chills and sensitivity to light and typically arise three to 10 days after infection.
Most people recover within several days to a month and symptoms typically last less than a week, the CDC said, though they often recur days or even weeks later.
A small proportion of people infected with Oropouche—fewer than 5%—go on to develop more serious disease including meningitis, brain inflammation and bleeding, though death is rare.
There are no medicines to treat Oropouche or vaccines to prevent infection available or in development and health experts say the best way to protect against the disease is to prevent bites from midges and mosquitoes in areas where the disease is known to occur such as using insect repellant and door and window screens.
Why Is Oropouche Called Sloth Virus Or Sloth Fever?
Oropouche is sometimes called “sloth virus” or “sloth fever” because it is found in areas where sloths are present, not because contact with sloths transmits the virus. Scientists believe the virus has a reservoir in pale-throated sloths, as well as non-human primates and some birds, which can help transmit the disease through the bites of midges or mosquitoes.
Why Is This Oropouche Outbreak Causing Concern?
The Oropouche virus is endemic in parts of South America and has been for quite some time now, which means infections and outbreaks are not necessarily unusual. However, experts say there are several noteworthy factors that make the current outbreak a cause for concern. For one, the outbreak appears to be sustained and larger than usual for Oropouche, with more than 8,000 cases confirmed by laboratory testing this year so far. It is also more geographically spread out than previous outbreaks, said Stephen Graham, a virology professor at the University of Cambridge, reaching as far north as Cuba and as far south as Sao Paulo state in Brazil and the CDC said the outbreak is occuring in both endemic areas and “new areas outside the Amazon basin” where the virus is usually found. Brazil has been heavily hit and Bolivia, Peru, Colombia, and Cuba are all among the countries that have reported locally acquired infections. Several others— including the United States (11), Spain (12), Italy (5) and Germany (2)—have reported cases linked to travel, though there are not yet signs the disease has established a foothold. There are several unusual factors that make this current outbreak concerning as well, in particular the first reports of deaths from the virus among two otherwise healthy, non-pregnant women in Brazil, the virus’ first known fatalities. There are also growing concerns over the ability of the virus to spread from mother to fetus during pregnancy and experts are investigating whether it is responsible for stillbirths, miscarriages or birth defects.
What We Don’t Know
Though Oropouche is not a new virus, there is a lot about it that we do not know, enough that the top tier Lancet medical journal described it as a “mysterious threat” in an editorial earlier this month. Scientists are also uncertain over what sparked the current outbreak, though they do have an idea. Oropouche virus is an RNA virus and its genome is made up of multiple segments, Graham explained, meaning the virus is “capable of rapid mutation” and of mixing and matching different segments—a process akin to shuffling two decks of cards known as “reassortment”—if “you are unlucky enough to be infected with two different strains.” Such genetic mixing opens up more opportunities for the virus to become more transmissible or pathogenic, Graham said. Experts believe there is evidence that this is what happened in Brazil to launch the current outbreak.
Tangent
Many of Oropouche’s initial symptoms are similar to “symptoms of dengue, chikungunya, Zika, or malaria,” the CDC said, and the virus is often undiagnosed or confused with them.
Crucial Quote
The features of Oropouche mean it is unlikely to spiral into a global pandemic like COVID-19, Cambridge’s Graham said. “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.”
Big Number
500,000. That’s how many cases of Oropouche fever have been recorded since the discovery of the virus, according to The Lancet.
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Further Reading
billionaire space race, the health impacts of overturning Roe v. Wade, outbreaks of infectious diseases like Covid-19, Nipah and mpox and Elon Musk’s feud with OpenAI’s Sam Altman to Musk’s rebranding of Twitter, the future of GLP-1 blockbusters like Ozempic, Wegovy and Mounjaro, generative AI systems like OpenAI’s ChatGPT and the real science inspiring fiction like The Last of Us.
Prior to joining Forbes, Rob covered big data, tech, policy and ethics as a features writer for a legal trade publication and worked as freelance journalist and policy analyst covering drug pricing, Big Pharma and AI. He graduated with master’s degrees in Biological Natural Sciences and the History and Philosophy of Science from Downing College, Cambridge University.
Follow Rob Hart for the latest on obesity drugs and AI, deep dives and ethical investigations on the industries of the future and updates on Elon Musk’s many ventures including SpaceX, Neuralink and X. Connect with him on X @ theroberthart or email at rhart@forbes.com
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