Over two dozen individuals who have returned to the United States from travels in Cuba have been diagnosed with Oropouche virus disease, colloquially referred to as "sloth fever," owing to the susceptibility of sloths to this pathogen. This recent surge in cases among travelers has led the Centers for Disease Control and Prevention (CDC) to issue a health advisory. The advisory emphasizes the importance of closely monitoring individuals returning from regions where the virus is known to circulate, such as Cuba, various parts of South and Central America, and the Caribbean.  

The Pan American Health Organization, which operates as the regional office for the World Health Organization in the Americas, has declared an epidemiological alert for the Oropouche virus. Concurrently, they have elevated the public health risk level to "high" across the Americas. Affected U.S. travelers have exhibited a range of symptoms including fever, muscle pain, and headaches, along with gastrointestinal issues like diarrhea, nausea, or vomiting, and skin rashes. Some have also reported experiencing recurring symptoms post-recovery, a phenomenon not uncommon among those afflicted with Oropouche virus disease.

Insights into Oropouche Virus

Dr. Chantal Vogels, an assistant professor of epidemiology at Yale School of Public Health, explains that the Oropouche virus has been predominantly found in South and Central America, as well as the Caribbean, with the first documented case in Trinidad and Tobago dating back to 1955. The primary mode of transmission for this virus is through the bite of biting midges, although certain species of mosquitoes are also capable of spreading it. These tiny insects, measuring less than 1/8 of an inch, are known to bite both humans and animals, with only the female midges engaging in this behavior.

Dr. Alex Greninger, a professor of laboratory medicine and pathology and the director of retrovirology at UW Medicine, points out that Oropouche shares significant similarities with the viruses responsible for Zika and dengue fever, which are primarily mosquito-borne. While Oropouche's transmission via midges is somewhat distinct, the symptoms it presents—such as fever, headaches, nausea, and vomiting—are quite comparable. Although severe illness is rare, there have been instances where the disease has led to cerebral swelling.

Concerns Raised by Health Officials

The rarity of Oropouche virus cases in the United States is contrasted by the alarming number of cases reported globally, the virus's expansion into new territories, and the fatal cases documented in Brazil, which have raised alarm bells among health officials. Dr. Vogels notes that since the latter part of 2023, the virus has been identified as the causative agent in substantial outbreaks in the Amazon regions and has been implicated in endemic transmission in new areas across South America and the Caribbean. This endemic transmission signifies a significant local spread, moving beyond isolated instances of travelers carrying the virus back to their home countries.

In July 2024, Brazil reported two fatalities linked to Oropouche virus, marking the first recorded deaths attributed to the virus in its nearly seven-decade history. Additionally, there have been worrisome reports of the virus being transmitted from mother to fetus, further escalating concerns.

Transmission Dynamics of Oropouche Virus

To grasp the spread of the Oropouche virus, it is crucial to examine its transmission cycle, which is bifurcated into the sylvatic-enzootic cycle and the urban-epidemic cycle, as elucidated by Dr. Vogels. In the sylvatic cycle, the virus is transmitted between biting midges or mosquitoes and animal reservoirs, such as sloths and non-human primates. The virus can then spill over into humans through the bite of an infected insect, potentially triggering an epidemic transmission cycle where humans become the hosts.

If an infected human or insect travels to a new area, the virus could initiate transmission there, provided the presence of suitable mosquito or midge vectors and a conducive climate. For instance, an individual might contract the virus in the Amazon region, return to their home country, and if bitten by another mosquito or midge while still carrying the infection, could spread the disease to others in their new locale.

Potential for Oropouche Virus Spread in the U.S.

Dr. Vogels clarifies that all reported U.S. cases are travel-related, with no evidence suggesting local transmission within the country. While the possibility of Oropouche spreading in regions of the U.S. where the relevant midge species are abundant cannot be entirely dismissed, the current risk of transmission in the U.S. is deemed to be low. Factors such as widespread access to healthcare, the prevalence of air-conditioning, and the use of screened windows in the U.S. contribute to reducing the likelihood of sustained transmission from cases associated with travel.

Treatment and Prevention of Oropouche Virus

Currently, there are no specific treatments or vaccines available for Oropouche virus, according to Dr. Greninger. Individuals experiencing mild symptoms can manage their condition through rest, hydration, and the use of over-the-counter pain relievers. However, those with severe symptoms are advised to seek immediate medical attention.

In the absence of vaccines or specific treatments, the prevention of insect bites stands as the most effective strategy to avert infection, as stated by Dr. Vogels. To this end, she recommends the following precautions:

• Use insect repellent: Apply insect repellents registered with the Environmental Protection Agency (EPA) that are proven effective against biting midges and mosquitoes.      
• Wear protective clothing: Opt for long-sleeved shirts, pants, and socks to minimize exposure of the skin.        
• Avoid peak activity times: Since mosquitoes are most active during dawn and dusk, reducing outdoor activities during these periods can lower the risk of being bitten.      
• Stay in screened or air-conditioned areas: This helps to prevent contact with insects that may carry the virus.
• Reconsider travel plans if pregnant: Pregnant individuals are advised to avoid non-essential travel to areas with a high risk of Oropouche virus transmission.

Dr. Vogels also emphasizes the importance of seeking medical care and informing healthcare professionals about one's travel history if experiencing any symptoms suggestive of Oropouche virus disease.