• DHS encourages health care providers to: 
  • Maintain an increased suspicion of OROV infection among patients with fever who have a history of travel to an area with documented or suspected OROV circulation within 14 days before illness onset.  
  • Contact the DHS Bureau of Communicable Diseases at dhsdphbcd@dhs.wisconsin.gov or 608-267-9003 to request OROV testing if indicated.  
  • Promote insect bite prevention measures during travel to areas with current or previous OROV transmission. If travel occurs during seasonal vector activity in Wisconsin, continue insect bite prevention for three weeks after return.
  • Counsel pregnant patients and patients planning pregnancy about the possible risks to a fetus of OROV infection during pregnancy.

Background 

Oropouche virus belongs to the Simbu serogroup of the genus Orthobunyavirus in the Peribunyaviridae family. OROV virus was first detected in 1955 in Trinidad and Tobago and is endemic in the Amazon basin. The current 2024-2025 outbreak is occurring in endemic areas and new areas outside the Amazon basin. Although travel-associated cases have been identified in the United States (n=109), no evidence of local transmission currently exists within the United States or its territories. Biting midges (Culicoides paraensis), also commonly called no-see-ums, and possibly certain mosquitoes (Culex quinquefasciatus) are primarily responsible for transmitting the virus to humans. 

The majority of people infected with OROV become symptomatic. The incubation period is typically 3–10 days. Initial clinical presentation is similar to diseases caused by dengue, Zika, or chikungunya viruses, or malaria, with abrupt onset of fever, chills, severe headache, myalgia, and arthralgia. Other symptoms can include retroorbital (eye) pain, photophobia (light sensitivity), dizziness, nausea, vomiting, or maculopapular rash that starts on the trunk and goes to the extremities. Symptoms typically last 2–7 days, however, symptoms reoccur a few days or even weeks later in up to 60% of patients. Clinical laboratory findings can include lymphopenia and leukopenia, elevated C-reactive protein (CRP), and slightly elevated liver enzymes.

Although illness is typically mild, it is estimated that up to 4% of patients can develop neuroinvasive disease (for example, meningitis, meningoencephalitis). Neuroinvasive disease symptoms may include intense occipital pain, dizziness, confusion, lethargy, photophobia, nausea, vomiting, nuchal rigidity, and nystagmus. Clinical laboratory findings for patients with neuroinvasive disease include pleocytosis and elevated protein in cerebrospinal fluid (CSF). 

It is possible that the risk of Guillain-Barré syndrome (GBS) may increase following an OROV infection. One report described three patients who developed GBS 10-11 days after initial symptom onset of OROV disease.

Cases of vertical transmission of OROV associated with adverse pregnancy outcomes such as fetal deaths and congenital abnormalities have been reported. It is still unknown how frequent vertical transmission occurs during pregnancy, whether the timing of infection during pregnancy impacts the risk of an adverse outcome, and the specific risk of fetal loss or congenital abnormalities after OROV infection. Based on limited data available, CDC (Centers for Disease Control and Prevention) has drafted Interim Clinical Considerations for Pregnant Women with Confirmed or Probable Oropouche Virus Disease.  

No cases of sexual transmission of OROV have been reported, but the virus was found in semen of a patient who had OROV disease. This raises the concern about possible risk of sexual transmission.  

Laboratory diagnosis is generally accomplished by testing serum. CSF can also be tested in patients with signs and symptoms of neuroinvasive disease. Diagnostic testing via real-time reverse transcription-polymerase chain reaction (RT-PCR) and/or plaque reduction neutralization test (PRNT) is currently available at CDC. All OROV testing must first be approved by an epidemiologist at DHS Bureau of Communicable Diseases.  

Who should be tested?  

Clinicians should consider OROV diagnostic testing in patients who have been in an area with documented or suspected* OROV circulation within two weeks of initial symptom onset (as patients may experience recurrent symptoms), and the following: 

• In the absence of a more likely clinical explanation, meets one of the following clinical criteria:
  • Acute onset of fever or chills or two or more of the following: headache, myalgia, arthralgia, retroorbital/eye pain, or generalized rash; or  
  • Meningitis, encephalitis, acute flaccid paralysis, or other acute signs of central or peripheral neurologic dysfunction, and

• Tested negative for other possible diseases, in particular dengue.ǂ  

*Suspected OROV circulation may include areas bordering or adjacent to countries or territories with documented OROV circulation.     

Clinical management 

No specific antiviral treatments or vaccines are available for OROV disease. Treatment for symptoms can include rest, fluids, and use of analgesics and antipyretics. Acetaminophen is the preferred first-line treatment for fever and pain. Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) should not be used to reduce the risk of hemorrhage. Patients who develop more severe symptoms should be hospitalized for close observation and supportive treatment. Pregnant people with laboratory evidence of OROV infection should be monitored during pregnancy and live-born infants should be carefully evaluated. 

Prevention 

Travelers to areas with OROV transmission should use prevention measures to avoid biting midge and mosquito exposure during travel and, if travel occurs during seasonal vector activity in Wisconsin, for three weeks after travel to mitigate additional spread of the virus and potential importation into the state. The primary vector of OROV, Culicoides paraensis biting midges, has been reported from one location in Wisconsin, and its distribution throughout the state is still unknown. Given the unknown distribution of Culicoides paraensis biting midges in Wisconsin and given Culex quinquefasciatus mosquitoes are not known to be present in Wisconsin, the potential for local transmission of OROV in the state is most likely low.

Individuals with suspected OROV infection, however, should still use measures to prevent bites for at least three weeks after return to avoid potential further spread of OROV. 

To prevent possible spread through sex, male travelers diagnosed with OROV disease should use condoms or abstain from sex for six weeks from the start of their illness. Male travelers with symptoms of OROV disease during travel or within two weeks of travel should consider using condoms or abstaining from sex for at least six weeks from the start of their illness and should speak to a health care provider about whether they should be tested for OROV.

Recommendations for local and Tribal health departments  

• Share OROV prevention messages for travelers and people who are or may become pregnant with health care providers, travel health clinics, and the public. 
• Investigate all suspect cases of OROV disease in travelers who have been in areas with OROV transmission. Local transmission of OROV in Wisconsin is possible, but unlikely given the primary vector (Culicoides paraensis biting midges) is present in Wisconsin but their statewide distribution is unknown and given Culex quinquefasciatus mosquitoes are not known to be present in Wisconsin.
• Individuals with suspected OROV infection, however, should still use measures to prevent bites for at least three weeks after return to avoid potential further spread of OROV.    
• Assist DHS and health care providers with obtaining appropriate testing for diagnosing OROV infection. 
• Contact DHS Bureau of Communicable Diseases at dhsdphbcd@dhs.wisconsin.gov or 608-267-9003, if any concern exists for local vector transmission or sexual transmission. Consider if the patient had contact with a person with confirmed OROV infection or has known vector exposure (for example, mosquitoes or biting midges). 

Recommendations for travelers  

• All travelers can protect themselves from Oropouche, dengue, Zika, and other viruses transmitted by insects by preventing insect bites, including using an Environmental Protection Agency (EPA)-registered insect repellent; wearing long-sleeved shirts and pants; and staying in places with air conditioning or that use window and door screens. 
• Pregnant travelers should discuss travel plans, reasons for travel, steps to prevent insect bites, and potential risk with their health care provider. 
• Pregnant people considering travel to countries with an OROV Level 2 Travel Health Notice should reconsider non-essential travel. If travel is unavoidable, pregnant travelers should strictly follow OROV prevention recommendations to prevent insect bites during travel.  
• Travelers should be aware that the most common symptoms of Oropouche virus are fever, headache, chills, muscle aches, and joint pain and that symptoms usually begin 3-10 days after being bitten by an infected midge or mosquito. Most people infected with OROV feel better within a week, but symptoms often come back. 
• Travelers who have been in areas with OROV transmission should prevent insect bites for three weeks after travel.  
• Travelers to areas with OROV transmission, including South America, Central America, or the Caribbean, who develop fever, chills, headache, joint pain, or muscle pain during or within two weeks after travel, should: 
  • Seek medical care and tell their health care provider when and where they traveled.
  • Not take aspirin or other NSAIDS (for example, ibuprofen) to reduce the risk of bleeding. 
  • Continue to prevent insect bites during the first week of illness to avoid further spread, especially in areas where mosquitoes or biting midges are active.  

• Male travelers with OROV should use condoms or not have from sex for at least six weeks from the start of their symptoms to avoid potential spread of the virus through sex.  
• Male travelers who develop symptoms of OROV infection (such as fever, chills, headache, joint pain, or muscle aches) within two weeks of returning from travel should consider using condoms or not having sex for at least six weeks from the start of their symptoms and talk with a health care provider about whether they should be tested.  

Resources

Questions 

Questions regarding this health alert may be directed to the Bureau of Communicable Disease at dhsdphbcd@dhs.wisconsin.gov.  

About the Wisconsin Health Alert Network  

The content of this message is intended for public health and health care personnel and response partners who have a need to know the information to perform their duties. The HAN will be the primary method for sharing urgent and time-sensitive public health information with clinical and public health partners. For more information about the HAN, including how to subscribe and unsubscribe, visit DHS' HAN webpage.