What is Oropouche virus?

Oropouche virus was first detected in 1955 in Trinidad and Tobago and is currently endemic in the Amazon basin, according to CDC. Previous outbreaks have occurred in Bolivia, Brazil, Colombia, Ecuador, French Guiana, Panama, and Peru.

Oropouche has also been nicknamed "sloth fever" or "sloth virus" because it has been found in areas where sloths are present. Contact with sloths, however, doesn't actually transmit the virus. Scientists believe the virus has a reservoir in pale-throated sloths, non-human primates, and some birds, which can help the virus travel through midge or mosquito bites.

According to CDC, around 60% of people infected with Oropouche develop symptoms, including fever, severe headache, muscle aches, chills, and joint pain. While the illness typically resolves after a few days, around 70% of people experience recurrent symptoms days or even weeks after their initial infection. Fewer than 5% of people who get the disease develop more serious conditions like meningitis, brain inflammation, or bleeding.

There are currently no vaccines to prevent or treat Oropouche, CDC said. Avoiding bug bites is the best way to prevent infection.

CDC issues warning about Oropouche virus

CDC's health advisory comes as Oropouche has led to more than 8,000 global cases this year as of Aug. 1 and caused two deaths, as well as five cases of fetal death or birth defects.

CDC has warned that pregnant women should reconsider any nonessential travel to countries where Oropouche is circulating, which currently includes Brazil, Bolivia, Peru, Colombia, and Cuba.

"If travel is unavoidable, pregnant travelers should strictly follow Oropouche virus prevention recommendations, to prevent insect bites during travel," CDC said.

The United States has seen 11 travel-related cases of Oropouche so far this year, CDC said, however there's no evidence the virus has begun circulating in North America.

Brazil has seen five cases of Oropouche in which infected pregnant women have lost their babies or had children born with birth defects, including microcephaly, a condition where a baby is born with a small, underdeveloped head.

CDC recommends that any travelers to nations affected by Oropouche avoid any biting midges and mosquitos during their travel and up to three weeks after returning home to prevent the spread of the virus to the United States.

"All travelers can protect themselves from Oropouche, dengue, Zika and other viruses transmitted by insects by preventing insect bites, including using an Environmental Protection Agency-registered insect repellent; wearing long-sleeved shirts and pants; and staying in places with air conditioning or that use window and door screens," CDC said.

While Oropouche isn't a new virus, some experts are expressing concern about the current outbreak, as it appears to be more sustained and larger than typical Oropouche outbreaks.

According to Stephen Graham, a virology professor at the University of Cambridge, the outbreak is also more geographically spread out than previous outbreaks, spreading as far north as Cuba and as far south as Sao Paulo state in Brazil. CDC has also said the outbreak is occurring in "new areas outside the Amazon basin" where the virus is typically found.

Graham said that Oropouche virus is an RNA virus with a genome made up of multiple segments, meaning that it's "capable of rapid mutation" and mixing and matching different segments if "you are unlucky enough to be infected with two different strains." This behavior provides more opportunities for the virus to become more transmissible or pathogenic, Graham said, which experts believe is what happened in Brazil to cause the outbreak.

However, Oropouche's features mean it's unlikely to turn into a global pandemic, Graham said. "The good news here is that most people recover completely from Oropouche virus infection within a few weeks, so this virus won't cause a [COVID-19] like global pandemic." (Thompson, U.S. News & World Report, 8/20; Sun, Washington Post, 8/17; Hart, Forbes, 8/19)

Over time, climate change has caused several disease-carrying species to become more widespread in the United States, significantly increasing the risk of certain diseases, such as West Nile virus and Lyme disease. However, experts say the United States isn't prepared for future outbreaks, Sara Van Note writes for STAT.