Two deaths linked to spreading ‘sloth virus’
Key Takeaways
Cases of Oropouche virus—also known as ‘sloth fever’—are on the rise. Discovered in 1955 in Trinidad and Tobago, the virus has made its way around the globe. It is considered to be both a neglected tropical disease and an emerging infectious disease.
Symptoms include but aren’t limited to fever, fatigue, joint and muscle pain, rash, and vomiting or diarrhea. Illness usually clears up entirely, but recurring sickness can occur. Two deaths have been reported.
People traveling to the Amazon basin should remain vigilant—especially pregnant women, the immunocompromised, and the elderly.
In 1955, a 24-year-old who worked in the forests of Trinidad and Tobago, near the Oropouche River, became the first human on record to contract the fever-inducing ‘sloth virus’ or Oropouche virus.[][] While the virus is endemic to the Amazon basin, it is now spreading globally.[]
It’s worth noting that the moniker ‘sloth fever’ refers to the fact that the virus was initially found in a sloth, leading scientists to believe that the sloth played a key role in its spread between insects and animals.[][]
Over the years, outbreaks of the arthropod-borne virus have been seen in both humans and animals in Bolivia, Brazil, Colombia, Ecuador, French Guiana, Haiti, Panama, and Peru.[] Beginning in late 2023, large outbreaks occurred, impacting previously affected and new areas in South America and the Caribbean.[]
Understanding the movement of the virus is tricky, however. Brian Labus, PhD, MPH, REHS, Assistant Professor in the Department of Epidemiology and Biostatistics at University of Nevada’sSchool of Public Health, tells MDLinx, “It's hard to say if it has spread to new areas or if we are just doing a better job looking for it. Oropouche virus has been overshadowed by other viruses that cause similar diseases, like dengue and chikungunya, that circulate in the same places—and our surveillance for it hasn't been very robust. Cases have been reported in the United States and Europe, but these have all been in people who were infected while traveling to endemic regions.”
As of August 16, 2024, 21 cases have been reported among U.S. travelers returning from Cuba.[] While most of these patients saw their symptoms resolve entirely, at least three had recurrent symptoms after resolution of their initial illness. Researchers say this occurs in about 60% of patients.[] Cases have been found, for example, in Florida and New York, according to The Washington Post.[]
Globally, the virus is thought to have affected over 500,000 people.[] Case numbers are expected to rise in the coming years due to climate change and migration patterns of both humans and animals. Chad L. Cross, PhD, MFT, PStat(R), of the PARAVEC Laboratory at the University of Nevada’s School of Public Health, tells MDLinx that because of the virus’s relatively recent discovery and its episodic behavior, it’s considered both a neglected tropical disease and an emerging infectious disease.
Patients are infected by the bite of a mosquito or midge (small fly) carrying the virus, not patient-to-patient transmission, Dr. Cross says. “If a human becomes infected and develops viral disease and then comes back to an urban area, then the urban cycle allows ready spread through vector feeding among humans,” he explains. For this reason, he says, anything that brings hosts, vectors, and pathogens together—like deforestation, wildfires, or long droughts—can bring about an epidemic.
Oropouche virus symptoms
Dr. Labus says that the symptomatology of Oropouche virus looks like that of many other viruses. “About 60% of infected people develop symptoms, most typically fever, fatigue, joint and muscle pain, a rash, and vomiting or diarrhea,” he says. “These symptoms last for less than a week, although they can reoccur weeks later. About one in 20 people progress to a more serious disease that affects the nervous system, but death from the disease is very rare.”
Researchers have also noted that there have been reports of patients with hemorrhagic symptoms or neurological complications associated with the virus.[]
The Centers for Disease Control and Prevention (CDC) says that sickness is usually self-limited, but there have been reports of two deaths in patients with Oropouche virus infection.[] More so, there are concerns over vertical transmission or transmission between mother and baby in utero.
Dr. Labus says that physicians can tell the Oropouche virus apart from other viruses by using a patient’s travel history as a diagnostic tool. “Oropouche can be considered in symptomatic patients who were in the areas with increased Oropouche virus activity—currently Brazil, Bolivia, Peru, Colombia, and Cuba—within two weeks of the onset of initial symptoms,” he says. But the disease does look very similar to other vector-borne diseases, like dengue, chikungunya, and zika, so laboratory testing will help differentiate. “The CDC recommends ruling out dengue virus infection as the two viruses circulate in the same areas,” Dr. Labus adds.
Dr. Cross notes that blood serum or cerebrospinal fluid can be tested to confirm infection.
What this means for you
Physicians should warn patients—especially pregnant, older, or immunocompromised patients—traveling to areas where Oropouche virus spreads to take extra caution to avoid insect bites. “Because of the danger to a developing fetus caused by the virus, pregnant people should reconsider travel to areas where the virus is currently spreading,” Dr. Cross stresses. Dr. Cross says that patients returning from these regions should also take caution not to be bitten by mosquitoes back home. “Once you return to your hometown, you should avoid insect bites, as well, so that if you are infected, then you minimize the probability of inadvertently spreading the disease to new areas,” he says.