Oropouche Virus

The Oropouche virus was first identified in 1955 in a forest worker from the village of Vega de Oropouche in Trinidad and Tobago, near the Oropouche river. It was later detected in a sloth in Brazil in 1960. Since then, there have been more than 30 outbreaks in those countries as well as Peru, Panama, Columbia, French Guiana, and Venezuela. 

Oropouche virus is an arbovirus like dengue, Zika, and Chikungunya. The virus naturally circulates among nonhuman primates, rodents, sloths, and birds in the Amazon forest. Humans can be infected by the bite of infected midges (Culicoides paraensis) and some mosquitoes (Culex quinquefasciatus). Biting midges are known as “no-see-ums.” They are so small they can fly through standard window screens. 

Between 2015 and 2022, there were only 261of Oropouche cases. The virus made a resurgence in the Americas in 2023. Since then, the virus has spread to Brazil’s densely populated east coast and throughout South America, Central America, and the Caribbean.

The Pan American Health Organization (PAHO) reported 16,239 cases from 11 countries and 1 territory in 2024, including four deaths. PAHO has confirmed 12,786 Oropouche cases in 11 countries in 2025, as of August 14. In both years, Brazil had the highest number of cases followed by Panama, Peru, Cuba, Columbia, Venezuela, and Guyana. 

Imported cases have been reported in Uruguay, Chile, Canada, and the United States. The United States has confirmed 109 cases of Oropuche virus. All of them involved people who had traveled to Cuba. In 2025, the United Kingdom confirmed three Oropouche virus cases in people who had traveled to Brazil.  

Oropouche virus has begun infecting people in urban areas far from forests. Climate change has increased temperatures and rainfall, which help create breeding grounds for mites and mosquitoes that transmit the virus. Deforestation and urbanization have caused people to encroach on the habitats of wild animals and increased the risk of viral transmission to humans. The virus has also undergone genetic reassortment that has increased its ability to replicate in mammalian cells. Infected people and sloths have higher viral loads in their blood, making it easier or biting insects to transmit the virus. 

Oropouche virus can be vertically transmitted from mother to fetus during pregnancy, with harmful consequences. Brazil has reported 22 fetal deaths, 5miscarriages, and 4 cases of fetal anomalies linked to Oropouche infections. Brazilian scientists have also found evidence that Oropouche virus infections can cause microcephaly. 

Oropouche virus might also be spread by sexual intercourse. The virus has been detected in the semen of an Italian man who became ill after returning from a trip to Cuba. The virus was still detectable 58 days after his symptoms began.

On August 1, 2024, the Pan American Health Organization (PAHO) issued an epidemiological alert urging increased prevention, surveillance, and diagnosis of Oropouche cases. 

On August 16, 2024, the CDC posted a Health Alert Network to notify clinicians and public health authorities about an increase in Oropouche virus disease in Cuba and parts of South America. The CDC urged clinicians to consider Oropouche virus in people who had traveled to countries with known cases within two weeks of their initial symptoms. CDC also instructed them to rule out dengue infection. CDC also recommended that male travelers who developed Oropouche symptoms after visiting endemic areas should consider using condoms or abstaining from sexual activity for at least 6 weeks from the start of their symptoms. 

Approximately 60% of people infected with Oropouche virus become symptomatic. The incubation period is 3 to 10 days. Oropouche virus infections typically cause an abrupt onset of fever, chills, severe headache, myalgia, and arthralgia. Symptoms typically last between 2 and 7 days. However, symptoms reoccur in up to to 60% of patients. 

Most cases are mild but approximately 4% of patients develop neuroinvasive disease. These patients experience intense occipital pain, dizziness, confusion, lethargy, photophobia, nausea, vomiting, nuchal rigidity, and nystagmus. CSF studies reveal elevated white blood cell count and elevated protein. 

Another 5% of patients can develop hemorrhagic manifestations including epistaxis, gingival bleeding, melena, menorrhagia, or petechiae. 

Preliminary diagnosis of Oropouche viral disease is based on the patient’s clinical symptoms, location, and activities that may have increased the risk of exposure. Unfortunately, the clinical presentation is often mistaken for other arboviruses such as dengue, chikungunya, and Zika viruses. 

Clinical laboratory findings include lymphopenia, leukopenia, elevated C-reactive protein (CRP), and slightly elevated liver enzymes.

The virus can be cultured from blood during the first few days of infection. Viral RNA can be detected by PCR for several more days. Toward the end of the first week of illness, IgM antibodies are detectable, followed by IgG antibodies. CSF can be tested in patients with signs and symptoms of neuroinvasive disease. 

References

Moutinho S. Virus spreading in Latin America may cause stillbirths and birth defects. Scienceinsider, July 20, 2024.

Clinical Overview of Oropouche Virus Disease, https://www.cdc.gov/oropouche/hcp/clinical-overview/index.html

CDC health Alert Network (HAN) Health Advisory, Increased Oropouche Virus Activity and Associated Risk to Travelers, CDCHAN-00515, August 16, 2024

Morrison A, White JL, Hughes HR, et al. Oropouche Virus Disease Among U.S. Travelers — United States, 2024. MMWR Morb Mortal Wkly Rep. ePub: 27 August 2024. DOI: http://dx.doi.org/10.15585/mmwr.mm7335e1

Schnirring L. As Oropouche cases continue in the Americas, PAHO urges countries to keep their guard up. CIDRAP, February 12, 2025. 

Fischer C, et al. The spatiotemporal ecology of Oropouche virus across Latin America: a multidisciplinary, laboratory-based, modelling study, The Lancet Infect Dis, published online April 14, 2025, DOI: 10.1016/S1473-3099(25)00110-0.