CDC issues travel health advisory for Oropouche or ‘sloth fever’

The agency warned that there has been an increase in cases of Oropouche – colloquially known as ‘sloth fever’ – in the Americas, originating from endemic areas in the Amazon basin, as well as newly infected areas in South America and the Caribbean.

The advisory noted that between 1 January and 1 August 2024, there have been more than 8,000 cases reported globally, including two deaths and five cases of ‘vertical transmission’ – when a disease is transmitted in utero from mother to foetus.

Countries reporting cases include Brazil, Bolivia, Peru, Colombia, and Cuba, the CDC said. Additionally: “In the US and Europe in 2024, travel-associated cases have been identified in travellers returning from Cuba and Brazil.” More cases are expected as testing and surveillance for the virus increase in the Americas.

The European Centre for Disease Prevention and Control (ECDC) has reported cases among 19 Europeans, including those in Spain and Germany, in the last couple of months.

The CDC advisory recommended that clinicians and public health authorities evaluate and test travellers who have been to impacted areas, and who display signs and symptoms consistent with Oropouche infection. Additionally, they should highlight prevention measures to mitigate additional spread and potential importation to currently unaffected areas such as the US.

Transmission and treatment

The virus typically exists in forested areas of the Amazon basin, and is usually transmitted between mosquitoes and non-human vertebrate hosts such as sloths, primates, domestic and wild birds, and rodents.

Humans may become infected while visiting such areas, and can introduce the disease to urban environments. From there, further transmission may occur within the urban area if the virus is picked up by local biting midges or certain kinds of mosquitoes.

No specific antiviral treatments or vaccines are available for Oropouche – the disease must be treated through a combination of rest, drinking ample fluids, and the use of analgesics and antipyretics. Patients with more severe symptoms should be hospitalised, while pregnant patients should be closely monitored.

Advice for travellers

The CDC also recommended that travellers take prevention measures to avoid midge and mosquito exposure when travelling to regions affected by the disease, and for the subsequent three weeks after their return.

The agency recommended using an Environmental Protection Agency (EPA)-approved insect repellent; wearing long-sleeved shirts and trousers; and staying in places with air conditioning, or that use window and door screens.

Pregnant travellers should discuss their travel plans and potential risks with their healthcare provider, and should reconsider non-essential travel to countries with an Oropouche level 2 Travel Health Notice. If travel is unavoidable, they should strictly follow the above Oropouche prevention recommendations.

Those travellers who return from areas affected by the virus, and who then display symptoms of the disease, should immediately seek out medical care, and should not take aspirin, ibuprofen, or other non-steroidal anti-inflammatory drugs (NSAID).

Symptoms

Approximately 60% of those infected with Oropouche virus become symptomatic, with the incubation period typically lasting three to 10 days, the CDC advised.

The initial clinical presentation is similar to other diseases such as dengue, Zika, and chikungunya, with symptoms including “acute onset of fever, chills, headache, myalgia, and arthralgia”.

Other symptoms can include “retro-orbital eye pain, light sensitivity, nausea, vomiting, diarrhoea, fatigue, maculopapular rash, conjunctival injection, and abdominal pain”.

Initial symptoms typically resolve after a few days, but a high proportion (70%) experience recurrent symptoms days or weeks after the resolution of the initial illness.

The disease is usually mild, although a minority (less than 5%) of patients can experience “haemorrhagic manifestations or neuroinvasive disease”. The agency warned that the risk factors for more severe cases were “not well-defined”, but that those aged over 65 and those with underlying medical conditions such as immune suppression, hypertension, diabetes, or cardiovascular disease” are believed more likely to be at risk.