BRAIN-swelling ‘sloth fever’ could be passed on in the womb, experts fear.
Their warning comes after a mum tragically lost her baby before it was born, following infection with the virus.
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The little-known disease is officially called Oropouche virus and tends to circulate between primates like sloths – hence its nickname.
But it’s occasionally passed on to humans through midge and mosquito bites.
Most Oropouche infections are mild, with symptoms similar to Dengue, including a headache, body pains, nausea, a rash and sensitivity to light.
Some individuals may also experience gastrointestinal symptoms, like sickness and diarrhoea.
In severe cases, the virus can also attack the brain leading to meningitis or encephalitis, which can be fatal.
Oropouche virus was found in Europe this summer for the first time, after it started spreading rapidly in Latin America.
Cases of the illness have cropped in Brazil in places that have previously remained unaffected, such as the state of Ceará, where 171 cases were flagged after June 2024.
Most cases were concentrated in the rural valleys of the Baturité Massif, as the fields fields serve as an ideal environment for a species of biting midge that’s been know to transmit sloth fever to humans.
A report published to the New England Journal of Medicine detailed the case of 40-year-old pregnant woman who got infected with Oropouche virus when she was 30 weeks along.
The authors said this case suggests sloth fever can be passed on to babies through the womb, in what they call “vertical transmission”.
The woman developed a fever, chills, muscle aches and a severe headache on July 24 this year.
She had been receiving routine prenatal care and been diagnosed with gestational diabetes that was being treated with medication.
The mum – who’d previously suffered a miscarriage at 24 during the first trimester of her pregnancy – also had four routine obstetric ultrasound examinations, none of which showed abnormalities.
After noticing some light vaginal bleeding and dark-coloured vaginal discharge on July 27, she sought medical help.
An ultrasound showed that her baby was a little larger than average, but no other red flags were identified, as both its heart rate and movement were normal.
The woman sought help again on August 5, as she continued suffering a fever and light vaginal bleeding.
She also told doctors that she’d noticed her baby moving less as of July 31.
Another ultrasound showed that the tot had passed away.
Medics tested the mum’s blood, which confirmed she’d been infected with Oropouche virus.
Testing for other bug-borne viruses like dengue, Zika, chikungunya, and Mayaro came back negative.
Oropouche virus: Everything you need to know
Oropouche fever is a disease caused by Oropouche virus.
It is spread through the bites of infected midges (small flies) and mosquitoes.
Symptoms of Oropouche fever are similar to dengue and include headache, fever, muscle aches, stiff joints, nausea, vomiting, chills, or sensitivity to light.
Severe cases may result in brain diseases such as meningitis.
Symptoms typically start 4–8 days after being bitten and last 3–6 days.
Most people recover without long-term effects.
There are no specific medications or vaccines are available.
Precautions
Travellers heading to affected areas should take steps to avoid bug bites.
The virus is endemic in many South American countries, in both rural and urban communities.
Outbreaks are periodically reported in Brazil, Bolivia, Colombia, Ecuador, French Guiana, Panama, Peru, and Trinidad and Tobago.
Wear tops with long sleeves and long trousers, apply insect repellent regularly, and sleep under a mosquito net if you are not in enclosed, air-conditioned accommodation.
Source: US Centre for Disease Control and Prevention
“Further testing did not reveal other infections or conditions that could cause stillbirth,” the report authors said.
The family consented for doctors to perform a minimally invasive tissue sampling on the baby boy.
They noticed no malformations but detected Oropouche virus in the tot’s cerebrospinal fluid, brain, lungs and liver, as well as in the umbilical cord and placenta.
The authors wrote: “These values confirmed that vertical transmission had occurred.”
They also sequenced the virus and confirmed that it was related to strains circulating in the country.
Medics said the stillbirth was linked to the ongoing sloth fever outbreak in Brazil.
They concluded: “These findings emphasise the risks of Oropouche virus infection in pregnancy and the need to consider this infection in pregnant women with fever or other suggestive symptoms who live in or visit regions in which the virus is endemic or emerging.”
In September, Brazil reported the world’s first deaths from the bug after two women in their early twenties passed away in the northeastern state of Bahia.
The two women, aged 21 and 24, suffered severe bleeding and hypotension and were reported dead on July 25.
At least 19 cases of Oropouche were reported in Europe for the first time in June and July, according to the European Centre for Disease Prevention and Control (ECDC) – with 12 in Spain, five in Italy and two in Germany.
But these cases were imported into Europe – 18 of the people infected had just travelled back from Cuba and one of them from Brazil.
The virus has been circulating in Latin America and the Caribbean for decades.
But a surge in cases of the bug was recorded in Brazil this year, according to the World Health Organization (WHO) – 7,284 , up from 832 in 2023.
Studies have suggested that the illness may also be passed from human to human through sex.
