U.S. health officials are warning travelers about a potentially deadly insect-borne virus known as sloth fever after U.S. travelers returned infected from Cuba.
The Centers for Disease Control and Prevention (CDC) reported Tuesday that 21 cases have now surfaced in the United States and 19 in Europe; all of the travelers returned from Cuba (and one from Brazil).
The Oropouche virus, commonly known as sloth fever, is endemic to the Amazon region in Central and South America and is spread by midges and mosquito bites.
The rare disease has been expanding its scope since late 2023, with more than 8,000 cases of Oropouche virus disease having been reported so far this year—most of them in Brazil, but Bolivia, Peru, Colombia, and Cuba have also been affected.
The disease was first detected in 1955 on the island of Trinidad, some 7 miles off the northeast coast of Venezuela. The virus got its moniker in 1960 when it was first detected in Brazil from a blood sample taken from a sloth.
Most patients experience fever, chills, muscle pain, joint pain, and headaches, the CDC said, with some suffering additional symptoms such as diarrhea, nausea or vomiting, and rash.
In exceptional cases, the disease can cause meningitis or encephalitis.
Symptoms usually appear very suddenly, three to 10 days after the initial infection, and last between two days and a week. As there is no vaccination or other antiviral treatment for Oropouche, doctors usually prescribe rest, plenty of hydration, and fever-reducing medication.
However, up to 70 percent of patients experience recurrent symptoms within days to weeks of recovering from their initial sickness, according to a Health Advisory from the CDC.
What’s more, the disease can, in some cases, be lethal. On July 23, authorities in Brazil reported three deaths; a 57-year-old man had died from the disease in April, and two otherwise healthy young women—ages 21 and 24—died as well, in May and March, respectively. All victims died in hospital within 3 and 4 days of the outbreak of the fever.
These cases are the first fatalities recorded since the virus was first identified nearly seven decades ago.
Brazilian officials are also investigating cases of fetal deaths and birth defects that the virus might have caused, which investigations have shown can spread from a pregnant woman to the fetus, known as vertical transmission.
So far, Brazil has reported one fetal death and one miscarriage in the state of Pernambuco, as well as four cases of newborns with a birth defect in which a baby’s head is smaller than normal as a result of the infection.
Three additional possible cases of vertical transmission are being investigated in the state of Pernambuco in relation to three fetal deaths, Brazilian authorities said.
Earlier this month, the CDC advised pregnant women to reconsider all non-essential travel to areas affected by the virus.
“Travelers to areas with Oropouche virus transmission should use prevention measures to avoid biting midge and mosquito exposure during travel and for 3 weeks after travel,” the CDC said.
Infected people should continue preventing insect bites to avoid further spread, the agency added.
The CDC recommends travelers use EPA-registered insect repellents, wear long-sleeved shirts and pants, stay in places with air conditioning, or use window and door screens.