US Records First Sloth Fever Cases After Cuba Travel

The United States has recorded its first cases of ‘sloth fever’ after 21 travellers returned from Cuba earlier in August carrying the oropouche (pronounced or-oh-poosh) virus.

The US Centers for Disease Control and Prevention (CDC) says most of those affected have made a full recovery from the insect-borne illness, though three patients continue to have recurring symptoms.

There is currently no evidence that the oropouche virus passes directly between people. It is believed to develop in tropical insects in Central and South America, which then transmit it to forest-dwelling animals - mainly sloths, as well as certain primates, rodents and birds.

Oropouche virus risks and regional spread

Although the likelihood of local transmission in the US is considered low, the Pan American Health Organization (PAHO) has recently issued an advisory asking member states to improve disease surveillance. Cases are rising for unexplained reasons across Central and South America and the Caribbean.

PAHO officials have expressed serious concern that the oropouche virus is reaching areas where it was not previously regarded as endemic, including Bolivia and Cuba. Public health specialists believe climate change, deforestation and unplanned urbanisation may be helping the disease spread.

No medicines are currently available to prevent or treat the ongoing outbreak. By July, the World Health Organization had recorded more than 8,000 cases across Bolivia, Brazil, Colombia, Cuba and Peru.

The oropouche virus is transmitted by at least two insects - a mosquito and a midge - and was initially identified in a three-toed sloth, giving rise to its informal name. In people, the viral illness can be readily confused with dengue fever, chikungunya, Zika or malaria. Symptoms can include a sudden fever, intense headache, diarrhoea, nausea, vomiting, chills, muscle pain or joint pain. On rare occasions, the infection can be fatal.

US sloth fever cases linked to Cuba travel

The Florida Department of Health (FLDOH) identified 20 of the travellers who returned to the US with sloth fever after the whole group tested negative for dengue. They had recently travelled to Cuba, where the oropouche virus has been circulating since June.

The remaining sloth fever case was detected in a traveller who arrived in New York state from Cuba.

"Oropouche and dengue viruses can co-circulate and cause similar symptoms" explain officials at the CDC; "patients with clinically suspected dengue should be managed according to dengue clinical management recommendations until dengue is ruled out."

European health authorities recently provided comparable advice after finding 19 sloth fever cases in travellers returning from South America.

Fatal cases and possible pregnancy risks

This is not the first oropouche virus outbreak to affect South and Central America. Since its initial detection in the Caribbean in 1955, about half a million people have been infected following bites from the midge Culicoides paraensis or a mosquito species known as Culex quinquefasciatus. Both insects occur in tropical areas.

Even so, this is the first occasion on which human deaths have been linked to the virus. Sloth fever has so far killed a 21-year-old woman and a 24-year-old woman in Brazil.

Experts are also concerned that the oropouche pathogen could have fatal consequences for foetuses, in a manner similar to the Zika virus. Antibodies to oropouche were recently detected in newborns with microcephaly in South America, a congenital condition that seriously affects brain development.

"Acknowledging that these observations are still in the initial stages of investigation and the true trajectory is unknown, the risk level for the region has been upgraded to high," PAHO warned on 3 August 2024.

It remains unclear whether insects found in other parts of the world can spread the pathogen. However, a recent study found evidence that a midge species present in the US and Canada could transmit oropouche if it became infected.

This may provide a pathway for the disease to begin spreading on another continent.

The CDC says it is collaborating with partners such as PAHO to gain a better understanding of how the disease is spilling over into people and why the present outbreak is occurring. Because of the possible risks during pregnancy, officials advise pregnant people to postpone travel to outbreak areas.

Avoiding mosquito bites while travelling in these locations is essential.