What is known about the Oropouche virus: how it is transmitted and what are the symptoms

The vectors are the mosquitoes Cx. quinquefasciatus and Aedes serratus and the sandfly Culicoides paraensis, as its main vectors (Canva)

The Oropouche virus was first described in 1955. It was identified from the serum of rural workers living near the Oropouche River in Trinidad and Tobago. There were then several outbreaks in Brazil towards the end of the last century. It is currently spreading throughout the Americas.

More cases of people affected by Oropouche fever are being detected in areas where the pathogen was already circulating. There has also been an expansion to areas of the Americas that had not previously reported cases, according to a warning from the Pan American Health Organization (PAHO).

This year also saw the first report of deaths associated with Oropouche infection, and “cases of vertical transmission related to fetal deaths and microcephaly in newborns” were identified, according to the health agency, based in Washington DC, United States.

This year it was discovered that the Oropouche virus can be transmitted from a pregnant person to the fetus in Brazil (AFP)

Taking into account the epidemiological situation, PAHO warned regarding the evolution of the spread of the virus: “The true trajectory is unknown.” For this reason, the risk level for the Region of the Americas was raised to “high” this month.

They clarified that this is based on “currently available information, with a moderate level of confidence and out of extreme caution.” Currently, there is no vaccine or specific treatment for the infection.

In an interview with Infobae, Dr. Paula Bergero, a researcher in mathematical models and infectious diseases at the Institute of Physicochemical, Theoretical and Applied Research (INIFTA), which is part of Conicet and the National University of La Plata, commented: “The risk is high, and it is a disease that has been little studied. I am concerned that it will be like dengue. Before 2009, dengue was very sporadic in cities like Buenos Aires. However, now it is established and cases are reported every year.”

The Oropouche virus was endemic in some areas of the Amazon. Since last year, cases began to be detected in non-endemic areas (Freepik)

The virus can be transmitted through the bite of various insects. After biting an infected person or animal, the insect can transmit the virus to a susceptible person. It is not transmitted from person to person.

The species of sandfly inhabits North America, Central America, the Caribbean and reaches Argentina and Uruguay. “It is abundant in the warm and rainy months,” according to information provided by the Argentine Ministry of Health on its website.

The virus has two transmission cycles. One cycle is wild: the reservoirs are vertebrates (primates, sloths and rodents), and its vectors are the mosquitoes Cx. quinquefasciatus and Aedes serratus and the gnat Culicoides paraensis, as its main vectors.

The second cycle is the urban epidemic cycle, in which the infection is maintained mainly between humans and the midge Culicoides paraensis.

Fever, headache, red spots on the skin, bleeding from the nose or gums, and vomiting are some of the symptoms of Oropouche (Getty Images)

Symptoms include sudden onset of fever, headache, joint stiffness, aches and pains, and in some cases, light intolerance, double vision, persistent nausea and vomiting. Signs may last five to seven days.

Symptoms are similar to those of other infections such as dengue fever. In rare cases, severe cases with aseptic meningitis may occur. Full recovery of those affected may take several weeks.

There is no specific treatment. “Patients should remain at rest, with symptomatic treatment and medical follow-up,” recommended the Ministry of Health of Brazil, which is the country most affected this year.

The sandfly that can transmit the Oropouche virus (Maria Luiza Felippe-Bauer, Oswaldo Cruz Institute)

Oropouche fever is generally mild to moderate in severity. People recover within 7 days. However, sporadic cases of aseptic meningitis have been documented.

Brazil recently reported two deaths from the virus as part of the ongoing outbreak in that country. These deaths are believed to be the first reports of fatal cases associated with the disease. The cases were in areas of active transmission of Oropouche during the ongoing outbreak on the southern coast of the state of Bahia, according to PAHO.

The law will guarantee a package of rights for women and pregnant people (Getty Images)

Yes. If the pregnant person is infected, she can transmit the pathogen to the baby. In 2024, Brazil was the first country in the world to confirm cases of vertical transmission (from mother to fetus) associated with infection by the Oropouche virus.

“The cases have evolved into fetal death and congenital anomalies. However, it is not yet possible to establish the frequency with which this occurs,” the Brazilian health ministry said.

There is still no vaccine or specific treatment for Oropouche (Getty Images)

As of July 30, 8,078 confirmed cases of Oropouche had been reported in five countries in the Americas: Bolivia, Brazil, Colombia, Cuba and Peru.

Autochthonous transmission has been documented in ten non-Amazonian states in Brazil, including some where no cases had previously been reported.

For Dr. Bergero, as prevention and preparation measures, “monitoring should be improved, studying the sandfly that can transmit the Oropouche virus and also the wild cycle of the infection, which is unclear. The disease should be considered within the framework of the One Health approach, because it is linked to what humans do to the environment, just like dengue, avian flu, mpox. Ultimately, we are the ones who create the opportunity for infections to pass to humans.”