Oropouche virus: warning as threat spreads beyond the Amazon

/ in Arboviral Disease, Climate Change, Editors' Picks, Featured Articles

As global health authorities grapple with a host of established infectious disease threats, a previously obscure virus is steadily expanding its reach beyond its traditional Amazonian stronghold. Oropouche virus, first identified in Trinidad and Tobago in 1955, has emerged as a significant public health concern across South America and the Caribbean, with recent outbreaks reported in Bolivia, Brazil, Peru, and Cuba, including cases among travellers returning to Canada and the United States.

The current situation

Since late 2023, Oropouche virus disease has experienced a notable geographic expansion. According to the Pan American Health Organization (PAHO), between January and August 2024, more than 8,000 cases were reported across Peru, Brazil, Colombia, Bolivia, and Cuba. Some areas are seeing the virus for the first time, indicating a troubling pattern of spread.

Brazil has been particularly affected, with 7,284 confirmed cases reported between January and July 2024, with the Amazon region accounting for 75.7% of these cases. Six states reported cases, while ten non-Amazonian states, including Bahía, Espírito Santo, Santa Catarina, Pernambuco, and others, reported autochthonous transmission for the first time.

The virus has also established a foothold in Bolivia (356 confirmed cases), Colombia (74 cases), Peru (290 cases), and Cuba, where health authorities declared the first Oropouche viral illness epidemic in May 2024 with 74 confirmed cases across two provinces.

Of particular concern, Brazil reported two deaths in Bahia involving females aged 21 and 24—the first documented fatalities in Brazil and the Americas caused by acute Oropouche virus infection. The patients experienced severe coagulopathy and liver involvement, which were determined to be the likely causes of their rapid deterioration.

Why is it spreading now?

The increased spread of Oropouche virus is linked to a convergence of environmental and human factors. Climate change has intensified rainfall and temperatures, which has expanded the habitats of the virus’s vectors—biting midges (Culicoides paraensis) and certain mosquito species including Culex quinquefasciatus.

Meanwhile, human activities are reshaping the landscape of transmission. Deforestation and urbanisation have altered the natural habitats of vectors and hosts, creating new opportunities for interaction between them and humans, increasing the risk of spillover and transmission. As Okesanya et al. (2025) note in their comprehensive review, “These same characteristics have a significant impact on the habitats of the reservoir hosts, driving them to proximate areas of peri-urban and urban areas where the vectors are abundant.”

Construction projects, particularly in the Amazon region, have historically been associated with Oropouche outbreaks. A notable example occurred in 1961 when approximately 11,000 human cases were documented in Belém City, Brazil, coinciding with the construction of the Belém-Brasília highway. The construction likely increased workers’ exposure to infected vectors.

Additionally, air travel has become a significant factor in the virus’s spread. The prompt movement of individuals across regions with active virus circulation allows Oropouche to be transported to non-endemic areas, where it can potentially establish new transmission cycles if suitable vectors are present.

The danger it poses

While most Oropouche infections result in mild, self-limiting disease, several concerning developments warrant attention from public health officials and clinicians.

The most alarming recent finding is the potential link between Oropouche virus infection during pregnancy and adverse outcomes including foetal death and congenital abnormalities. According to a PAHO Public Health Risk Assessment from August 2024, in Brazil, one foetal death and one miscarriage were reported in Pernambuco, as well as four cases of newborns with microcephaly possibly linked to Oropouche virus.

These complications mirror those observed in Zika virus infections, which caused widespread concern during previous outbreaks. Das Neves Martins et al. (2024) documented newborns with microcephaly in Brazil with potential vertical transmission of Oropouche virus, reinforcing the need for enhanced surveillance and protective measures for pregnant women.

Additionally, neurological complications, although rare, have been documented. The virus has been detected in the cerebrospinal fluid of patients, and some have developed aseptic meningitis. There have also been cases of Guillain-Barré syndrome potentially associated with Oropouche infection under investigation.

The fatalities reported in Brazil highlight another concerning aspect of Oropouche virus disease—its potential to cause severe coagulopathy and liver involvement in some patients. While such severe manifestations appear to be rare, they demonstrate that the virus can occasionally cause life-threatening illness.

From a public health perspective, the emergence of Oropouche virus in new geographic areas poses significant challenges. Healthcare systems in affected regions, particularly those already struggling with other endemic diseases like dengue, malaria, and Zika, face additional burdens. The similar clinical presentation of these diseases complicates diagnosis and may lead to misdiagnosis or underreporting of Oropouche cases.

What can be done to stop it?

Controlling the spread of Oropouche virus requires a multifaceted approach targeting both the vector and human exposure. Vector control measures remain a cornerstone of prevention efforts:

1. Enhanced entomological surveillance: Strengthening monitoring of biting midge and mosquito populations can help identify areas at high risk for transmission.
2. Habitat modification: Reducing breeding sites for Culicoides paraensis by eliminating or treating organic debris, banana stems, and other decaying plant material can help control vector populations.
3. Targeted insecticide application: Strategic use of insecticides in areas with high vector density can reduce transmission risk.

Personal protective measures are equally important, particularly for individuals living in or travelling to affected areas:

1. Use of fine-mesh mosquito nets on doors and windows to prevent entry of biting midges and mosquitoes.
2. Protective clothing that covers arms and legs, especially during peak biting times.
3. Application of effective repellents containing DEET or icaridin, and use of bed nets while sleeping.

For pregnant women or those planning pregnancy, the Public Health Agency of Canada recommends considering deferring travel to areas experiencing Oropouche outbreaks. If travel cannot be avoided, strict adherence to protective measures is essential.

Health systems strengthening is also crucial for responding effectively to Oropouche outbreaks:

1. Enhanced surveillance systems to detect cases early and monitor the geographic spread of the virus.
2. Improved diagnostic capacity, including wider availability of polymerase chain reaction (PCR) testing for Oropouche virus.
3. Training of healthcare workers to recognise and appropriately manage Oropouche virus disease.
4. Cross-border collaboration to share information and coordinate response efforts.

Currently, there is no specific antiviral treatment or vaccine for Oropouche virus, highlighting the importance of prevention measures. However, research efforts are underway to develop both therapeutic options and vaccines.

 

Understanding Oropouche virus disease

 

Virology and transmission

Oropouche virus is an arbovirus of the genus Orthobunyavirus, belonging to the family Peribunyaviridae. The virus maintains both sylvatic (forest) and urban transmission cycles. In the sylvatic cycle, hosts include sloths, non-human primates, and certain birds, with forest mosquitoes like Aedes serratus and Coquillettidia venezuelensis serving as vectors.

In the urban cycle, humans are the primary amplifying host, with Culicoides paraensis (biting midges) and Culex quinquefasciatus mosquitoes serving as the main vectors. Biting midges are smaller than mosquitoes and can pass through conventional mosquito nets, requiring fine-mesh nets for effective protection.

Vertical (mother-to-child) transmission has recently been documented and is still under investigation, adding another dimension to the virus’s transmission dynamics.

Clinical presentation and diagnosis

The incubation period for Oropouche virus is typically 3–10 days. The disease presents as an acute febrile illness with symptoms similar to other arboviral infections, making clinical diagnosis challenging.

Common symptoms include:

• Sudden fever (usually lasting up to five days)
• Severe headache (often located posteriorly and continuing even after fever subsides)
• Extreme weakness (prostration)
• Joint and muscle pain (usually generalised)
• Chills
• Photophobia
• Dizziness
• Retroocular pain

Additional symptoms may include nausea, vomiting, diarrhoea, and low back pain. Up to 60% of cases are reported to have relapses of symptoms in the weeks following recovery, a distinctive feature of Oropouche virus disease.

While serious complications are rare, the disease can progress to aseptic meningitis, which usually manifests in the second week of illness, prolonging recovery by weeks. Haemorrhagic manifestations, including petechiae, epistaxis, and gingival bleeding, have been reported in some cases, though they are uncommon.

Laboratory findings may include leukopenia, lymphopenia, high C-reactive protein levels, and elevated liver enzymes. Thrombocytopenia has been documented in some cases.

Confirmation of Oropouche disease requires laboratory testing, as the clinical presentation overlaps significantly with other arboviral infections. The diagnostic test of choice is PCR of blood and urine samples within 7–10 days of symptom onset. Serological tests for Oropouche-specific antibodies can also be used, though cross-reactivity with other arboviruses may complicate interpretation.

Treatment and management

There is currently no specific treatment or vaccine for Oropouche virus disease. Management is supportive and focuses on symptom relief:

• Rest and adequate hydration
• Acetaminophen for fever and pain control
• Monitoring for possible complications

Importantly, nonsteroidal anti-inflammatory drugs should be avoided due to the risk of hemorrhage, similar to recommendations for other arboviral infections.

Most patients recover completely within a week, though some experience prolonged convalescence, particularly those who develop neurological complications.

Conclusion

As Oropouche virus continues its geographic expansion beyond its traditional Amazonian stronghold, heightened vigilance, enhanced surveillance, and robust preventive measures are essential to limiting its impact. The virus’s ability to cause severe disease in some patients, its potential for adverse pregnancy outcomes, and its adaptability to new environments underscore the importance of a coordinated public health response.

While not yet a global crisis, Oropouche virus serves as a reminder of the dynamic nature of infectious disease threats and the need for continued investment in disease surveillance, vector control, and healthcare system strengthening to address emerging pathogens.

 

References

• Cardoso, B. F., Serra, O. P., Heinen, L. B. da S., Zuchi, N., de Souza, V. C., Naveca, F. G., et al. (2015). Detection of Oropouche virus segment S in patients and in Culex quinquefasciatus in the state of Mato Grosso, Brazil. Memórias do Instituto Oswaldo Cruz, 110(6), 745–754.
• Das Neves Martins, F. E., Chiang, J. O., Nunes, B. T. D., et al. (2024). Newborns with microcephaly in Brazil and potential vertical transmission of Oropouche virus: a case series. Lancet Infectious Diseases. Published online October 15, 2024. doi: https://doi.org/10.1016/S1473-3099(24)00617-0 .
• Dinh, T., Kanji, J., & Vaughan, S. (2025). Five things to know about … Oropouche virus. Canadian Medical Association Journal, 197, E244. doi: https://doi.org/10.1503/cmaj.241440
• Okesanya, O. J., Amisu, B. O., Adigun, O. A., Ahmed, M. M., Agboola, A. O., Kab, T., et al. (2025). Addressing the emerging threat of Oropouche virus: implications and public health responses for healthcare systems. Tropical Diseases, Travel Medicine and Vaccines, 11(1), 1-19.
• Pan American Health Organization. (2024). Epidemiological update: Oropouche in the Americas region. Washington, DC: Pan American Health Organization, World Health Organization.
• Pan American Health Organization. (2024). Oropouche virus disease factsheet. Retrieved from https://www.paho.org/en/topics/oropouche-virus-disease
• Public Health Agency of Canada. (2024). Travel health notices: Oropouche virus disease in the Americas. Ottawa: Public Health Agency of Canada. Available at: https://travel.gc.ca/travelling/health-safety/travel-health-notices/534
• Travassos da Rosa, J. F., de Souza, W. M., Pinheiro, F., de Figueiredo, P., Cardoso, J. F., Acrani, G. O., et al. (2017). Oropouche Virus: Clinical, Epidemiological, and Molecular Aspects of a Neglected Orthobunyavirus. American Journal of Tropical Medicine and Hygiene, 96(5), 1019–1030. https://doi.org/10.4269/ajtmh.16-0672