What is Oropouche fever? Why is it in the news? | 2024 Oropouche virus outbreaks

According to the World Health Organization (WHO), Oropouche virus disease was the second most common arboviral disease in South America. The virus is endemic to the Amazon basin in South America and the Caribbean [1, 2].

The Oropouche virus was first discovered in a febrile forest worker in Trinidad in 1955 [1, 3]. The first epidemic, however, was recorded in 1961 in Belem, Brazil. Since then, more than 30 epidemics and over half a million clinical cases have been reported in Brazil, Peru, Panama, Trinidad and Tobago. Human infection has also been reported in Ecuador and French Guiana [2].

Until 2024, most people had not heard of the virus, but a wave of Oropouche outbreaks suddenly thrust it into the spotlight.

2024 Oropouche outbreaks

Between December 2023 and October 2024, over 10,000 Oropouche cases were reported, including where it had not been seen before. 8,000 of these cases were in Brazil alone. Cuba, the Dominican Republic, and Guyana reported their first Oropouche cases in 2024 [1].

Plus, Oropouche cases linked to travelers were also detected in the United States, Canada, Spain, Italy, and Germany [4].

Most alarming is the report of the first Oropouche-related deaths in Brazil, where two women succumbed to the disease [5].

Additionally, in August 2024, a fetal death was reported. This was the first documented case of vertical transmission for Oropouche. Vertical transmission is when a person transfers an infectious pathogen to their fetus or newborn infant [6].

Despite these numbers, experts feel that the actual case count may be significantly higher. This is because several obstacles remain before we can gain a realistic picture, including the fact that:

• Testing for the virus is limited
• Specialized labs are necessary
• Oropouche is often misdiagnosed at point-of-care facilities because symptoms resemble dengue fever and other arboviral infections [1, 2, 7].

GIDEON provides comprehensive data on Oropouche outbreaks, including case counts, detailed country notes, an extensive list of clinical references, and more.

The Oropouche virus spreads through Culicoides paraensis biting midges or Culex quinquefasciatus mosquitoes [8]. Biting midges, also known as no-see-ums, resemble tiny flies; their bites often appear similar to mosquito bites. The insect’s activity level is highest at dawn and dusk.

Can Oropouche spread from person to person?

The Oropouche virus does not spread from person to person. One 2024 report discovered the presence of Oropouche in semen [9]. However, there is no conclusive evidence yet that an OROV infection may be spread through sex; more research is needed.

Not much is known about how the Oropouche virus infects humans, including why symptoms may recur after they subside. The Oropouche virus can lead to a body-wide infection and systemic inflammation in the Central Nervous System (CNS). Clinical research is underway to understand the exact pathogenesis of the Oropouche virus [7].

People living in dense, urban areas in endemic regions are at a higher risk as biting midges can infect many people within the same vicinity. Those with heart disease, including hypertension, face a higher risk of severe Oropouche fever and increased mortality from the infection. People who are pregnant are at risk of transmitting the virus to their fetuses [2].

Most people infected with the Oropouche virus will experience symptoms within 3-10 days of getting infected (incubation period) [1].

Common symptoms of Oropouche include:

• Fever (acute febrile illness)
• Severe headache
• Chills
• Muscle pain
• Joint pain
• Sensitivity to light [1, 10].

Other signs of Oropouche fever may include:

• Dizziness
• Nausea
• Vomiting
• Eye pain
• Diarrhea
• Abdominal pain
• Severe symptoms may include bleeding from the gums, stool, or petechiae (tiny spots on the skin from bleeding under the skin) [1, 10].

Symptoms last 2-7 days but, in the majority of cases, recur a few days or a few weeks later. Oropouche is not often severe, and people usually recover from the infection.

Unfortunately, Oropouche fever is often misdiagnosed as other diseases. This is because its symptoms are similar to dengue, chikungunya, malaria, and other arboviruses [11]. As a result, it’s important for healthcare providers to gather information about a patient’s activities before infection.

A patient’s travel details are valuable to help improve diagnostic accuracy, especially if the individual has visited areas with Oropouche outbreaks [1, 11].

Laboratory diagnosis includes using tests like reverse transcription polymerase chain reaction (RT-PCR), real-time RT-PCR, and serological assays. However, the tests are not easily available and have to be performed by skilled workers in specialized labs [10].

There is no specific treatment for an Oropouche virus infection. The best way to treat Oropouche is to manage symptoms with over-the-counter medication like acetaminophen.

Please consult a healthcare provider before starting any medication regimen for Oropouche fever.

The best way to avoid Oropouche virus disease is to prevent bites from biting midges and mosquitoes in endemic regions. There are no vaccines to protect against Oropouche virus disease.

Prevention strategies include:

• Effective insect repellants to minimize bug bites
• Using mesh screens in areas prone to Oropouche outbreaks
• Limiting outdoor activities during twilight hours when biting midge activity level is highest.

Note: Oropouche has been detected in semen, but there are no reports indicating sexual transmission [9]. To be safe, male travelers may use condoms and abstain from sex for a minimum of 6 weeks from the onset of symptoms.

Currently, there are no licensed vaccines to protect against Oropouche fever.

The Oropouche virus is not a new one; it has been commonly found in South America and the Caribbean. However, case counts have been relatively low, and since the virus has a low mortality rate, it hasn’t gotten much global attention. This situation changed in 2024. The rise in Oropouche cases, including in previously non-endemic countries, has intensified outbreak surveillance efforts.

Much remains to be learned about this virus, including its definitive hosts and true case numbers. Better outbreak surveillance, improved point-of-care testing, increased awareness, and effective vector and disease control could help contain, treat, and even prevent Oropouche virus outbreaks.

Global collaboration between public health officials, epidemiologists, and healthcare providers can help advance the fight against infectious diseases like Oropouche virus disease.

1. What is the life cycle of the Oropouche virus?

The Oropouche virus has two life cycles. This viral infection can be spread through two ways. One cycle is the sylvatic cycle, where a biting midge or mosquito passes the virus to a reservoir host like a sloth, non-human primate, or certain wild birds. This tends to occur in highly forested areas, like the Amazon basin [8].

Another transmission cycle involves a more direct relationship with humans. Biting midges and certain mosquitoes feed on human blood and transmit the virus. The biting midge species C. paraensis is linked to urban cycle transmission [8].

2. What is the incubation period of Oropouche fever (Oropouche virus disease)?

Oropouche incubation period is 3-10 days. Symptoms usually last about a week [1, 10].

3. Can symptoms of Oropouche virus disease be confused with other diseases?

Yes, Oropouche fever symptoms look a lot like those of dengue, chikungunya, or malaria [7]. To treat Oropouche virus disease, physicians need to consider recent outbreaks, any travel to affected areas, or contact with people who might have traveled from these regions.

4. What are the complications of Oropouche virus disease?

While most people recover from Oropouche disease, in cases of severe illness, the virus can cause abnormal bleeding. It can even cause encephalitis and meningitis, inflammation in the brain and surrounding tissues. Another complication is that pregnant women can transmit an Oropouche infection to their unborn fetuses, leading to birth defects [12].

5. Why is Oropouche known as ‘sloth fever’?

Oropouche virus disease, or Oropouche fever, is also called ‘sloth fever’ because the virus was first isolated from sloths in 1960. Eventually, researchers learned that sloths are one reservoir host for the Oropouche virus. Others include non-human primates and even some wild birds [2, 3].

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