Mysterious Oropouche virus spreads: what you need to know

Once trapped Amazon RegionA mysterious virus that causes a disease called Oropouche fever has been expanding its range since late 2023, sparking international concern. The virus has already caused more than 8,000 infections in the Americas this year, mostly in Brazil, but also in Peru, Bolivia, Colombia and Cuba.

Brazilian authorities reported in July that two adults had died from the disease, the first time such deaths have occurred since the virus was identified nearly 70 years ago. Brazilian authorities are also investigating fetal deaths and birth defects that may be caused by the virus, which is known to be transmitted from pregnant women to their fetuses. There is no targeted vaccine or treatment for the disease.

Earlier this month, the Pan American Health Organization The risk level for Oropouche has been raised from medium to high.Citing the geographic spread of the virus and the occurrence of fatal cases in an illness historically known to cause mild to moderate symptoms, the World Health Organization on August 23rd declared: The virus poses a high public health risk at the local levelwhich is low by global standards. Recommendation: Close monitoring of people returning from affected areasThe United States, Spain, Italy and Germany have confirmed cases of Oropauche in travelers from Brazil and Cuba.

Nature We spoke with Gonçalo Bello, a public health expert at the Oswaldo Cruz Institute in Rio de Janeiro, Brazil, who is studying the lineage of Oropouche virus currently circulating in the Americas.

What is Oropoush?

Oropouche is a virus of the genus. OrthobunyavirusThis is different from other well-known vector-borne viruses. Dengue fever, Zika fever, yellow fever or Chikungunya fever This is because it is usually transmitted to humans by midges. Curicoides paraensisIt is also possible that other vectors, rather than mosquitoes, may be involved. [The virus has been found in other insects, including the mosquito Culex quinquefasciatus.]

How long has this virus been around?

It was discovered in the Caribbean island of Trinidad and Tobago in 1955. It was first detected in sloth blood samples in Brazil in 1960. Since the 1960s, human infections have been reported more or less intermittently in the Amazon region. [a vast area that spans nine countries in South America]We call it a re-emerging virus because, at least in the Amazon, where it is endemic, it has been circulating for decades.

Why are we only hearing about this now? Is this the biggest outbreak we've seen?

As for the Amazon region, it is difficult to say whether the current epidemic is larger than in previous decades, as for the first time a molecular surveillance and diagnostic system has been introduced that did not exist during previous epidemics.

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The geographical spread of the infection marks a change: the number of affected municipalities and states is now much higher. In addition, the virus has spread outside the Amazon region. Again, no surveillance of Oropouche has been carried out outside the Amazon until now, so we do not know if this is the first time.

There are also concerns that Cuba has confirmed its first locally transmitted infections, and that imported cases have been reported in Europe and the United States. Curicoides paraensis Chironomids are found throughout the Americas, from the United States to Argentina, and local transmission can occur when there is an infected individual and a vector, meaning that an infected individual can cause a local outbreak, which is the main concern.

What are the symptoms?

Symptoms [those of] Other arboviruses, such as dengue, can cause fever, headache, muscle and joint pain, pain behind the eyes, vomiting, and nausea. Therefore, it is very difficult to diagnose Oropausche infection based on symptoms alone, and molecular biology testing is really necessary. Although a small number of cases can develop into a more severe form with neurological and hemorrhagic symptoms, most cases are mild and resolve within 7-8 days.

Is the virus getting more dangerous? Could it cause microcephaly, a condition in which babies have abnormally small heads?

For the first time, the presence of antibodies against Oropouche, indicating recent infection, MicrocephalyAlthough this suggests an association, study limitations meant that a causal relationship between intrauterine infection and neurological malformations could not be established.

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However, in cases of fetal or neonatal death, it has been possible to establish evidence of mother-to-child transmission. In one case, a pregnant woman showed symptoms of Oropouche and the fetus died a few weeks later. Oropouche genomes were detected in several organs of the fetus. In another recent case, a pregnant woman tested positive for Oropouche. The baby was born but died a few days later. Postmortem examination identified the viral genome in various tissues, including the brain.

Two previously healthy young women, who were not pregnant, also died after developing severe dengue-like symptoms. These are the first documented cases classified as deaths associated with Oropouche infection.

It is not yet possible to determine how frequently these fatal cases occur, either in adults or in fetuses, and so far there is no evidence that symptoms have changed compared to previous outbreaks.