Experts fear that “sloth fever”, which causes swelling of the brain, could spread to the womb.
Their warning comes after a mother tragically lost her child before his birth, after he was infected with the virus.
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The little-known disease is officially called Oropouche Virus and tends to spread among primates such as sloths, hence its nickname.
But it is sometimes transmitted to humans through fly and mosquito bites.
Most cases of Oropouche infections are mild, with symptoms similar to dengue fever, including headache, body aches, nausea, rash, and sensitivity to light.
Some individuals may also experience gastrointestinal symptoms, such as illness and diarrhea.
In severe cases, the virus can also attack the brain resulting in meningitis or encephalitis, which can be fatal.
The Oropouche virus was found in Europe this summer for the first time, after it began spreading rapidly in Latin America.
Cases of the disease in Brazil have appeared in places previously unaffected, such as the state of Ceara, where 171 cases were reported after June 2024.
Most cases have been concentrated in the rural valleys of the Bathuretti Massif, where fields serve as an ideal habitat for a species of biting flies known to transmit sloth fever to humans.
Report published for New England Journal of Medicine She detailed the case of a 40-year-old pregnant woman who contracted Oropouche virus when she was 30 weeks pregnant.
The authors said that this case indicates the possibility of sloth fever being transmitted to children through the womb, in what they call “vertical transmission.”
The woman developed fever, chills, muscle aches and a severe headache on July 24 this year.
She was receiving routine prenatal care and was diagnosed with gestational diabetes, which was treated with medications.
The mother – who previously suffered a miscarriage at the age of 24 during the first three months of her pregnancy – also underwent four routine maternity ultrasounds, none of which showed any abnormalities.
After noticing light vaginal bleeding and dark vaginal discharge on July 27, she sought medical help.
The ultrasound showed that her baby was slightly larger than average, but no other red flags were identified, as her heart rate and movement were normal.
The woman sought help again on August 5, as she continued to suffer from fever and light vaginal bleeding.
She also told doctors that she noticed her baby moving less as of July 31.
Another ultrasound showed that the baby had died.
Paramedics tested the mother's blood and confirmed that she was infected with the Oropouche virus.
Other insect-borne viruses such as dengue, Zika, chikungunya and mayaro have tested negative.
Oropouche virus: everything you need to know
Oropouche fever is a disease caused by the Oropouche virus.
It is spread by the bites of infected midges (small flies) and mosquitoes.
Symptoms of Oropouche fever are similar to those of dengue fever and include headache, fever, muscle pain, joint stiffness, nausea, vomiting, chills, or sensitivity to light.
Severe cases may lead to brain diseases such as meningitis.
Symptoms usually begin 4 to 8 days after being bitten and last 3 to 6 days.
Most people recover without long-term effects.
There are no specific medications or vaccines available.
Precautions
Travelers heading to affected areas should take steps to avoid insect bites.
The virus is endemic in many South American countries, in both rural and urban communities.
Outbreaks of the disease are periodically reported in Brazil, Bolivia, Colombia, Ecuador, French Guiana, Panama, Peru, and Trinidad and Tobago.
Wear long-sleeved shirts and long pants, use insect repellent regularly, and sleep under a mosquito net if you are not in enclosed, air-conditioned accommodation.
source: US Center for Disease Control and Prevention
“Additional testing did not reveal infections or other conditions that could cause stillbirth,” the report authors said.
The family agreed to have doctors perform a minimally invasive tissue biopsy on the infant.
They did not notice any abnormalities but detected Oropouche virus in the baby's cerebrospinal fluid, brain, lungs and liver, as well as in the umbilical cord and placenta.
“These values confirmed the occurrence of vertical transmission,” the authors wrote.
They also sequenced the virus and confirmed that it was linked to strains circulating in the country.
Medics said the stillbirth was linked to the ongoing sloth fever outbreak in the country Brazil.
They concluded: “These findings underscore the risks of Oropouche virus infection during pregnancy and the need to consider this infection in pregnant women with fever or other suggestive symptoms who live or visit areas where the virus is endemic or emerging.”
In September, Brazil announced the world's first death from this bacteria after two women in their early twenties died in the northeastern state of Bahia.
The women, ages 21 and 24, suffered severe bleeding and low blood pressure and were reported dead on July 25.
At least 19 cases of Oropouche were first reported in Europe in June and July, according to the European Center for Disease Prevention and Control (ECDC) – with 12 cases in 2019. Spainfive in Italy And two in Germany.
But these cases were imported to Europe, where 18 of those infected had just returned from Cuba and one of them was from Brazil.
The virus has been spreading in Latin America and the Caribbean for decades.
But a rise in cases of the disease has been recorded in Brazil this year, according to the World Health Organization – 7,284, up from 832 in 2023.
Studies indicate that the disease may also be transmitted from one person to another through sex.
