Oropouche virus: what is 'sloth fever'? Signs and symptoms as first cases of 'unstoppable' virus found in US

• Cases of the Oropouche virus have been detected in Europe and the US for the first time.
• Dubbed ‘sloth fever’, the virus is mainly spread by mosquito bites.
• An outbreak of the virus has been reported across countries in South America.
• Although fatal outcomes are rare, two people in Brazil have already died after contracting the virus.

Cases of the Oropouche virus, which has been dubbed “sloth fever”, have been detected in the US for the first time. This comes after the virus, which got its nickname due to originating in sloths was also confirmed in Europe in early August.

Outbreaks of the virus, which is spread by bites from mosquitoes and midges, have been reported in South America in 2024, with over 8,000 infections detected detected across Brazil, Bolivia, Colombia, Peru and Cuba, but cases have started to be reported elsewhere.

The Centre for Disease Control have confirmed that a total of 21 cases have been detected in the US so far amongst travellers returning from Cuba, with three experiencing recurrent symptoms. They have urged travellers to protect themselves from insect bites when travelling in areas experiencing an outbreak.

In early August, the European Centre for Disease Control (ECDC) confirmed that there have been 19 cases of the virus confirmed in Europe so far, with 12 in Spain, five in Italy and two in Germany.

Eighteen of the cases recorded had recently travelled to affected areas in South America where they are thought to have caught the virus.

Speaking to The Telegraph, Dr Danny Altmann, Professor of Immunology at Imperial College London, has voiced his concerns. Dr Altmann warned: "We should definitely be worried. Things are changing and may become unstoppable."

What is ‘sloth fever’?

Oropouche is a virus that is transmitted to humans by insect bites, such as mosquitoes and midges. It originates from pale-throated sloths, which is why it has been given the nickname, “sloth fever”.

What are the symptoms of Oropouche virus?

Most cases of Oropouche are mild, with symptoms including headache, nausea, vomiting, muscle and joint pains, with symptoms normally easing after four days.

However in some circumstances there can be severe symptoms and in rare cases it can be fatal. In Brazil, two women with no underlying health conditions died after contracting the virus on July 25, according to The Lancet.

The risk and impact of infection during pregnancy is still under investigation and has not been confirmed, but it’s believed being infected with the virus during pregnancy may lead to miscarriage, developmental problems, or deformities of the foetus.

What is the advice?

There is no vaccine or medicine approved to treat Oropouche, the ECDC has classed the risk to tourists travelling to an area in South America impacted by an outbreak as “moderate”.

The likelihood of catching the virus in Europe is “very low” as the midges and mosquitos that transmit it are absent and there have been no documented cases of human-to-human transmission.

For anyone travelling to an area affected, the ECDC recommends: "The use of repellent in accordance with the instructions indicated on the product label, wearing long-sleeved shirts and long trousers and using insecticide-treated fine mesh mosquito bed nets when resting.”

They add: "These measures are essential to provide protection against bites in rooms that are not adequately screened (with fine-mesh screens on doors and windows) or air-conditioned, and during outdoor activities."

You can learn more about how to avoid mosquito bites on NHS.UK.