The Oropouche virus is spreading in South America as scientists warn of possible outbreaks in the United States

As cases of the Oropouche virus rise across South America, experts are calling for urgent action to prevent its spread, with the US potentially at risk due to travel-related cases.

Summary: Reemergence of Oropouche virus in the Americas and risk of spread in the United States and its territories, 2024. Image source: CI Photos / Shutterstock

In a recent review published in the magazine Emerging infectious diseasesResearchers reviewed available information on the epidemiology, diagnosis, and transmission risk associations of Oropouche virus (OROV) (genus). Orthobunyavirus). Reports indicate that the disease has re-emerged and spread throughout its distribution area, particularly since the end of 2023. In just nine months (January-September 2024), more than 9,000 cases and two deaths were reported in six South American countries, including additional reports of travel-related cases in North America and Europe, highlighting the need to review preparedness ahead of a possible large-scale disease outbreak.

The results of the review indicate that the risk of Oropouche virus transmission is low in most parts of the United States. Still, some areas, including Puerto Rico and South Florida, are considered at increased risk of disease due to the frequent influx of potential carriers from Oropouche virus hotspots. Cuba, which is experiencing an active outbreak, has also contributed to the rising number of cases among travelers returning to the United States and Europe. Lessons from previous vector-borne outbreaks and current studies of transmission ecology in Cuba and other affected regions could inform future preparedness for the disease. In particular, given the limitations of current small (S) segment targeted genomic testing, more effective and specific detection and testing methods need to be developed.

What is Oropouche virus infection and what are its causes?

The Oropouche virus is a pathogen that belongs to the Simbu serogroup of the genus Orthobunyavirus (Peribunyaviridae Family). The virus was first detected in a feverish forest worker in Trinidad and Tobago near the Oropouche River. Transmission to humans occurs primarily through bites Culicoides paraensisa kind of biting mosquito. Until recently, the virus was considered endemic to the Amazon basin. Reports from before 2000 documented outbreaks in Brazil, Peru and Panama. Recent reports have observed the disease spreading to Argentina, Bolivia, Colombia, Ecuador, French Guiana and Haiti between 2000 and 2023.

Worryingly, despite previous declines in the prevalence of Oropouche virus disease across South America, the past year (January to September 2024) has seen numerous local outbreaks, causing more than 9,000 infections and at least two deaths in just six Latin American countries. Notably, Cuba, previously unaware of the disease, reported its first confirmed case in June 2024, sparking concerns about the disease's rapid transmission and outbreak potential.

Although nearly seven decades have passed since its initial discovery, scientific knowledge of the Oropouche virus is still limited. In particular, there are currently no vaccines, cures, or routine confirmatory diagnostic tests for the disease, presumably due to its predominantly mild clinical symptoms and limited long-term effects. Recent disease-related mortality and unprecedented range expansion have raised concerns about possible viral shifts and highlighted the need for additional epidemiological research on this disease.

Symptoms, transmission and diagnosis

Oropouche virus disease typically presents with a sudden onset of high fever, severe headache, chills, myalgia, and arthralgia. Unfortunately, these symptoms overlap with those of dengue fever, Zika virus, malaria, and chikungunya fever, often leading to misdiagnosis and sometimes masking outbreaks of Oropouche virus disease as a result of persistent episodes of malaria or dengue. In severe cases, oropouche virus disease can cause neurological symptoms including retro-orbital pain, dizziness, nausea, vomiting, and retro-orbital or eye pain. In rare cases, symptoms may include severe abdominal pain, conjunctivitis and bleeding.

Pathogen transmission generally occurs through either urban or forest transmission cycles. The urban cycle is better documented and involves the back and forth transmission of pathogens between infected people Culicoides paraensis and people. While Culex quinquefasciatusthe southern house mosquito, has been suggested as a transmission vector, previous assessments of vector competence have questioned this assumption with inconclusive results. However, the less understood sylvate transmission cycle requires extensive research given the potential for a wide range of mammalian and avian hosts, including sloths, non-human primates, wild rodents and birds.

Despite the high infection rate of the disease (up to 30% of the population can be infected in a single incident), the diagnosis of Oropouche virus disease remains challenging due to the lack of a dedicated diagnostic test and its symptomatic similarity to other vector-borne viral diseases (dengue, malaria , Zika). Although current reverse transcription-polymerase chain reaction (RT-PCR) assays can detect viral load, these tests remain sensitive only for the first 5-7 days after infection, raising the need for the development of more sensitive and specific diagnostic tests against the virus pathogen underlined.

Spread Risk and United States Preparedness

Despite the alarming increase in the prevalence of Oropouche virus disease, current epidemiological studies indicate that the risk of epidemic events in the United States is low. This is primarily due to the small range overlap between urban US residents and Culicoides paraensis, with the latter generally restricted to rural tree hollows in the Midwest and Southeastern US

“Oropouche virus disease is not a nationally reportable disease, but state and territorial health departments may voluntarily report identified cases to ArboNET. In addition, if Oropouche virus occurs in the United States, the Board of State and Territorial Epidemiologists may decide whether to make Oropouche virus notifiable at the national level and determine whether a new case definition should be developed to record potential fetal deaths or congenital infections, as was previously done for the Zika virus.”

Increased public health preparedness is essential, particularly in areas such as South Florida and Puerto Rico, where introduction of the virus via travelers is more likely. The U.S. can improve its outbreak preparedness by requiring physicians to report suspected patients to public health authorities, encouraging routine investigation of local cases with similar symptoms, and implementing community-wide mitigation measures, including pest control (to prevent transmission from forest animals). Since rare cases of vertical transmission from mother to fetus have been documented, pregnant women should be monitored and information about the disease should be widely disseminated.

“Past experience with several emerging and re-emerging vector-borne diseases as well as new information on Oropouche outbreaks (e.g., transmission ecology in Cuba) will help inform and refine Oropouche virus preparedness, detection, and response . Public health partners should prioritize timely detection and control of this emerging pathogen to prevent human cases and spread of the virus.”