A primer on Oropouche virus

Thomas A. Moore, MD, FACP, FIDSA

9/13/2024

Oropouche virus, an arbovirus of the Orthobunyavirus group native to forested tropical areas, is the latest addition to the steadily growing collection of emerging infections this century. Originally isolated in 1955 from the blood of a 24-year-old forest worker in Vega de Oropouche, Trinidad (1), the virus has since been found circulating in the Amazonian region of South America, causing sporadic cases and outbreaks. (2)

Beginning in late 2023, it was identified as the cause of large outbreaks in Amazonian regions with known endemic transmission, but also in new areas in South America and the Caribbean. (3)

Oropouche fever is also known as sloth fever, after investigators of the original case identified the virus in a three-toed sloth. The virus has a sylvatic cycle, infecting pale-throated sloths, nonhuman primates and birds. It is primarily transmitted through the bite of a midge (Culicoides paraensis) and mosquitoes (Aedes spp) in the Amazon region.

However, due to the unholy trinity of climate change, deforestation and unplanned urbanization, the illness has spread to other, non-Amazonian areas of Brazil and to countries in which no cases had previously been reported — specifically, Bolivia and Cuba. Additionally, in the current outbreak, disease has developed in persons living far from forested areas, and certain mosquitoes (e.g., Culex quinquefasciatus) appear to act as additional vectors, suggesting that the virus now also has an urban cycle of transmission. (4)

Reported cases and symptoms

In addition to approximately 8,000 locally acquired cases in the Americas, travel-associated disease cases have recently been identified in European travelers returning from Cuba and Brazil. (5) As of Aug. 16, 2024, the Centers for Disease Control and Prevention had reported a total of 21 Oropouche virus disease cases among U.S. travelers, all of whom had returned from Cuba. (3)

The symptoms of Oropouche fever are identical to other arboviral illnesses (dengue, chikungunya, Zika), making it difficult to distinguish between them clinically. After an incubation period of 3-10 days, patients typically experience the abrupt onset of fever, severe headache, arthralgias, myalgias, and in some cases, maculopapular rash, photophobia, retro-orbital pain, conjunctival injection and abdominal pain. Rarely, hemorrhagic manifestations (petechiae, epistaxis, melena, gingival bleeding) or aseptic meningitis and encephalitis may occur. (6)

Most of the 21 U.S. cases reported by CDC initially experienced fever, myalgia and headache, often with other symptoms including arthralgias, nausea/vomiting, diarrhea and rash. At least three patients, however, experienced recurrent symptoms after the initial illness, a commonly noted characteristic of Oropouche virus disease.

Oropouche fever is not universally benign. In July, Brazil reported the deaths of two young women without any known comorbid illnesses. The possibility of vertical transmission is also being investigated after reports of Oropouche virus disease associated with one case of fetal demise, one miscarriage and four cases of microcephaly.

The Pan American Health Organization issued an epidemiologic alert concerning possible vertical transmission of Oropouche associated with adverse pregnancy outcomes, including fetal death and congenital malformations. (7)

Testing and treatment

Diagnostic testing is available through CDC for patients who meet testing criteria. Suspected cases are those with clinically compatible illness and exposure to areas with Oropouche virus circulation who tested negative for dengue. The presence of cough and other pulmonary symptoms are exclusionary.

Testing is performed using a 90% plaque reduction neutralization test to detect virus-specific neutralizing antibodies in serum or cerebrospinal fluid, with titers >10 considered positive. Specimens collected <7 days after symptom onset are tested using a real-time RT-PCR assay. (8)

There are no vaccines or specific antiviral treatments for Oropouche fever. Management of the disease is symptomatic. Until a vaccine becomes available, prevention will rely upon the use of personal protective measures to prevent insect bites.

For more information on increases in Oropouche virus activity and associated risks for travelers, see CDC’s Aug. 16 Health Alert Network advisory. The Aug. 28 CDC/IDSA Clinician Call, which focused on dengue and other vector-borne diseases, also included information on Oropouche virus. Watch the call recording.

Photo: An adult biting midge

References

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