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      Oropouche

      Latest update: - Authors: Eline Lambert, Félix De Bièvre, Nele Alders, Ula Maniewski

      Introduction

      Oropouche virus (OROV) is an arbovirus belonging to the Simbu serogroup of the viral genus Orthobunyavirus of the family Peribunyaviridae. The virus was first detected in 1955 in a febrile forest worker in a village in Trinidad and Tobago, near the Oropouche River. OROV is mainly transmitted by midges and is endemic to the Amazon basin. 

      Transmission

      Vector

      Oropouche virus spreads through insect bites, mainly by midges and some mosquitoes. Midges are tiny flies, usually one to three millimetres long. The risk of midge biting is highest at dawn and dusk, but they are active throughout the whole day and night. Midges found in the European territory do not currently spread Oropouche virus disease. In urban areas, certain Culex mosquitos have also been found to carry the virus, though midges remain the main vector. 

      Reservoirs and life cycle

      Transmission of Oropouche virus is mainly maintained in a sylvatic cycle in forested areas between the midge Culicoides paraensis and non-human vertebrate hosts, including sloths, certain non-human primates, and birds. In the urban cycle, humans are the amplifying host. 

      Risk for traveller 

      Infections in travellers are rare. However, the risk is perceived as moderate for those travelling to regions experiencing an outbreak and may vary locally, for example in the northern states of Brazil and the Amazon region.

      Incubation period    

      3–4 days (range 1–10 days).

      Symptoms

      The majority of people infected with Oropouche virus become symptomatic. Symptoms are similar to those of other arthropod-borne diseases, such as dengue, zika or chikungunya. Symptoms include sudden fever, severe headache, myalgia, fatigue, chills and arthralgia. Other signs and symptoms can include photophobia, dizziness, retro-orbital pain diarrhoea, nausea/vomiting, abdominal pain, maculopapular rash and back pain. Although most people recover within a week, up to 60% of cases experience relapses of symptoms days to weeks after recovery. Most Oropouche cases are mild, but severe disease and death have been reported. Severe manifestations of illness include haemorrhagic symptoms (e.g., gingival bleeding, melena, and menorrhagia), neurologic symptoms (e.g., meningitis, meningoencephalitis, Guillain-Barré syndrome), and adverse pregnancy outcomes.

      There is currently no specific treatment for Oropouche virus. Management of the disease is supportive.

      Pregnancy and outcomes

      For pregnant woman the clinical manifestations and complications of OROV infection appear to be similar to nonpregnant individuals. Mother-to-child transmission has been documented and is still under investigation. The significance of the timing of maternal infection and the absolute risk of abnormal pregnancy outcomes are uncertain. 

      The Oropouche viral RNA has been detected in vaginal secretions of patients with Oropouche virus disease. During the 2023-2024 outbreak, several pregnant women infected with OROV had miscarriages or stillbirth. Placental, umbilical blood and foetal organ samples of stillborn foetuses tested positive for OROV by Polymerase Chain Reaction (PCR). In addition, a retrospective Brazilian study found that in some infants with microcephaly of unknown cause, cerebrospinal fluid samples tested positive for IgM antibodies to OROV.

      These findings are all consistent with maternal OROV viremia resulting in transplacental transmission, in line with multiple other bunyaviruses showing a tropism for foetal and placental tissues, causing abortions, foetal losses, and multiple congenital deformities in pregnant livestock.

      At present, the significance of these signals is not clear yet. Further research is needed to determine whether a causal relationship exists between infection and congenital malformations.

      Culturable virus was also detected in semen, but currently no cases of sexual transmission have been described.

      Risk areas

      Prior to the year 2000, outbreaks of Oropouche virus were reported in Brazil, Panama, and Peru. In the early 2000s, cases of Oropouche have been identified in many countries in South America. 

      In late 2023, Oropouche virus was identified as causing large outbreaks in endemic areas and new areas in South America, Central America and the Caribbean. 

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      Additional information

      • PAHO for most recent epidemiological information 

      References

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