Epidemiological UpdatesPublic Health Risk Assessment
Oropouche virus disease (OROV) is a febrile infection caused by an arbovirus of the genus Orthobunyavirus, belonging to the family Peribunyaviridae. First identified in 1955 in Trinidad and Tobago, OROV has caused cases and outbreaks in several South American countries, including Brazil, Colombia, Ecuador, French Guiana, Panama, Peru and Venezuela. Outbreaks have been most frequent in the Amazon Basin region, where the most known vector, the midge (Culicoides paraensis), maintains a sylvatic cycle involving hosts such as sloths and non-human primates.
Symptoms of Oropouche fever include sudden fever, severe headache, extreme weakness (prostration), joint and muscle pain. In some cases, photophobia, dizziness, persistent nausea or vomiting, and low back pain may occur. Fever usually lasts up to five days. Although serious complications are rare, the disease can progress to aseptic meningitis, which usually manifests in the second week of illness, prolonging recovery by weeks. Up to 60% of cases are reported to have relapses of symptoms in the weeks following recovery.
The increased spread of OROV is linked to a variety of environmental and human factors. Climate change has intensified rainfall and temperatures, while deforestation and urbanization have altered the natural habitats of vectors and hosts, favoring interaction between them and increasing the risk of transmission.
To control the spread of OROV, vector prevention and control measures are recommended. This includes strengthening entomological surveillance, reducing midge populations, and educating the population on personal protection measures. Specific recommendations include using fine-mesh mosquito nets on doors and windows, clothing that covers arms and legs, repellents with DEET or icaridin, and fine-mesh nets over beds or sleeping areas.
- Since late 2023, outbreaks of Oropouche virus disease have been reported in several countries in South America and the Caribbean, including areas with no previous history of this disease.
- As of August 16, 2024, 9,852 cases of Oropouche have been confirmed in the Region of the Americas, including two adult deaths. These cases are distributed in seven countries: Bolivia, Brazil, Colombia, Cuba, Dominican Republic, Guyana, Peru, and the Dominican Republic.
- According to a PAHO Public Health Risk Assessment (August 2024) in Brazil, one fetal death and one miscarriage have been reported in the state of Pernambuco , as well as four cases of newborns with microcephaly possibly linked to OROV. A similar outbreak occurred in Manaus between 1980 and 1981, with nine infected pregnant women, two of whom suffered miscarriages.
- Confirmation of Oropouche disease is done by molecular and serological testing in laboratories with adequate capacity; there is no rapid test available.
- There is no specific treatment or vaccine for Oropouche. Management includes rest, hydration, and the use of medications to control fever and pain, as well as monitoring for possible complications.
- Four genotypes of Oropouche virus have been identified. Infection with any of these genotypes should induce antibody production, providing protection against future reinfection.
Oropouche virus is a re-emerging virus in the Americas, transmitted to people mainly through infected midges and some species of mosquitoes. Oropouche has been observed to be emerging outside the Amazon Basin, in previously unaffected areas.
In addition, as of September 2024, two deaths in infected persons have been reported so far in Bahia, Brazil. Infection during pregnancy has been linked to fetal death and possible birth defects. Neurological cases (Guillain Barre syndrome) possibly associated with OROV infection are also under study.
Transmission
OROV is transmitted mainly through the bite of the midge Culicoides paraensis, which inhabits wooded areas and near bodies of water, and certain mosquitoes such as Culex quinquefasciatus. Viral circulation is suspected to include both sylvatic and urban cycles. In the jungle cycle, primates, sloths and possibly some birds act as vertebrate hosts. In the urban cycle, humans are the amplifying host. Vertical (mother-to-child) transmission has been documented recently and is still under investigation.
Symptoms
Symptoms are similar to those of dengue and begin four to eight days after the infecting bite. Signs include sudden fever, severe headache, extreme weakness (prostration), joint and muscle aches, chills, nausea, diarrhea, and persistent vomiting. Approximately 60% of cases experience relapses of symptoms weeks after recovery. Although most recover within a week, some patients have a prolonged convalescence. Serious complications, such as aseptic meningitis, are rare, but may occur in the second week of illness.
Treatment and vaccine
There is currently no specific treatment or vaccine against Oropouche virus. Management of the disease is supportive and focuses on symptom relief, such as rest, hydration and the use of fever and pain medications, as well as monitoring the patient for possible complications, such as arterial hypotension, intense sweating leading to rapid dehydration and especially nervous system manifestations, such as meningitis, meningoencephalitis and Guillain-Barré syndrome. In case of severe manifestations, cases should be hospitalized.
Recommendations
- Vector control: Strengthen entomological surveillance, reduce mosquito and gnat populations, and educate the population on personal protective measures.
- Preventive measures for travelers: Travelers to affected areas should take precautions against insect bites, using repellents with DEET or icaridin, protective clothing and mosquito nets.
- Recommendations for pregnant women: According to the U.S. Centers for Disease Control and Prevention (CDC), pregnant women are advised to reconsider non-essential travel to areas with a Level 2 Travel Health Advisory for Oropouche virus due to the risk of mother-to-child transmission.
PAHO/WHO urges Member States to intensify surveillance for the timely detection of cases, train health personnel in the clinical detection and management of the disease and inform the population at risk about preventive measures. It also stresses the importance of laboratory diagnosis to confirm cases and monitor disease trends.
