Oropouche virus ‘massively underdiagnosed’ in Latin America, new study suggests

Oropouche virus may be far more widespread in Latin America than previously understood, new research has found.

Closely related to the Zika and Dengue viruses, Oropouche is transmitted by biting midges and mosquitoes. It poses a particular risk to pregnant women, having been linked to stillbirths and serious birth defects.

The virus was first detected outside of Brazil – where it is endemic – in October 2023, when it began spreading rapidly across other South American and Caribbean countries. Since then, over 20,000 cases and four deaths have been reported. 

However, a new study published in The Lancet Infectious Diseases suggests that the virus may have been circulating across the region undetected since as early as 2001.

Researchers analysed 9,400 blood samples collected between 2001 and 2022 from patients in Bolivia, Colombia, Costa Rica, Ecuador, and Peru. They found that at least 6.3 per cent – nearly 600 individuals – had antibodies against Oropouche, indicating past infection.

There were significant regional variants, however; while antibodies were present in two per cent of samples from Costa Rica, they appeared in five per cent of samples from Ecuador and over 10 per cent of samples from the Amazon region. 

People living in higher altitudes were also less likely to have experienced a previous Oropouche infection than those at warmer, lower altitudes – which offer more favourable conditions for the insects that transmit the disease. 

“Our data show that Oropouche virus is massively under-diagnosed in Latin America,” said Professor Jan Drexler, head of the Virus Epidemiology Laboratory at the Institute of Virology at Charité and lead author of the study. 

“We still know relatively little about the virus, the consequences of an infection, including on unborn babies, require further investigation and it’s not yet clear whether there are parallels with the Zika virus,” he added. 

The researchers said that Oropouche cases are often confused with dengue fever, which is widespread in Latin America, because they cause similar symptoms including high fevers, headaches, and muscle pain.

The study also found the El Niño phenomena – a naturally occurring weather pattern which creates warmer and wetter weather – significantly increases transmission of Oropouche, by creating conditions in which midges and mosquitoes can thrive. The 2023-2024 El Niño was one of the strongest on record, and was exacerbated by climate change.

“I think it’s possible that Oropouche virus will become even more widespread in the future as climate change progresses,” Dr Drexler said.

The authors of the study say the findings emphasise the need for the development of an Oropouche vaccine, which currently does not exist. 

They also recommend that healthcare workers in the Americas are better educated on the signs and symptoms of Oropouche virus, and that it should be considered when treating anyone with unexplained fevers, pregnancy complications, or in the case of unexplained death.

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