Oropouche Virus Disease Among U.S. Travelers — United States, 2024

Natural History and Clinical Symptoms

Oropouche virus (Simbu serogroup, genus Orthobunyavirus) is endemic to the Amazon region and was previously identified as a cause of human disease in several countries in South and Central America and the Caribbean (1). The virus circulates in a sylvatic cycle, possibly involving certain vertebrate hosts (e.g., sloths, nonhuman primates, and birds) and mosquitoes, and an urban cycle in which humans serve as amplifying hosts with known vectors being biting midges (Culicoides paraensis) and possibly mosquitoes (e.g., Culex quinquefasciatus) (1).

The clinical signs and symptoms of Oropouche virus disease are similar to those of other arboviral diseases such as dengue, Zika, and chikungunya. After an incubation period of 3–10 days, patients typically experience abrupt onset of fever, chills, headache, myalgia, and arthralgia. Other symptoms might include retroorbital pain, photophobia, vomiting, diarrhea, fatigue, maculopapular rash, conjunctival injection, and abdominal pain. Initial symptoms usually last only a few days, but up to 70% of patients are reported to have recurrent symptoms within days to weeks after resolution of their initial illness (2). Although illness is typically mild, hemorrhagic manifestations (e.g., epistaxis, gingival bleeding, melena, menorrhagia, and petechiae) or neuroinvasive disease (e.g., meningitis and meningoencephalitis) can rarely occur (1,3,4). No vaccines to prevent or medicines to treat Oropouche virus disease exist; treatment is supportive.

Recent Outbreaks in South America and Cuba

During December 2023–June 2024, large Oropouche virus disease outbreaks were recognized in areas with known endemic disease, and the virus emerged in new areas in South America and Cuba where it had not been historically reported (3). As of August 2024, over 8,000 laboratory-confirmed cases have been reported in Bolivia, Brazil, Colombia, Cuba, and Peru (3). These large outbreaks have resulted in travel-associated cases, with 19 Oropouche virus disease cases in European travelers returning from Cuba (n = 18) and Brazil (one) during June–July 2024 (5). Recently, cases of severe disease leading to two deaths and vertical transmission associated with fetal death and possible congenital malformations in Brazil have raised concerns about the threat of Oropouche virus to human health (3).

Identification of U.S. Cases

CDC and New York State Department of Health (NYSDOH) Wadsworth Center conducted Oropouche virus testing for travelers who had returned from areas with known Oropouche virus circulation and had an illness that was clinically compatible with Oropouche virus disease. Clinical diagnostic testing at CDC’s Arboviral Diseases Branch and NYSDOH Wadsworth Center Arbovirus Laboratory is performed using a 90% plaque reduction neutralization test (PRNT₉₀) to detect virus-specific neutralizing antibodies in serum or cerebrospinal fluid, with titers ≥10 considered positive. CDC also conducted surveillance testing on specimens collected ≤7 days after symptom onset using an Oropouche virus real-time reverse transcription–polymerase chain reaction (RT-PCR) assay (6). This activity was reviewed by CDC, deemed not research, and was conducted consistent with applicable federal law and CDC policy.*

The Florida Department of Health (FLDOH) identified suspected cases primarily by reviewing patients who received negative test results for dengue from state and commercial laboratories and who had a clinically compatible illness and exposure to areas with potential Oropouche virus circulation. Details of epidemiologic investigations, including risk factors, clinical features, and outcomes, are captured from patient interview, clinician interview, or review of medical records using a standardized case investigation form.

Characteristics of U.S. Cases