What is ‘Sloth Fever’? And How Can I Avoid It When Travelling to South America?

International authorities are issuing warnings about “sloth fever.” Despite the name, it’s not contracted via contact with sloths. Instead, it is spread by mosquitoes and biting midges.

What is ‘Sloth Fever’?

Sloth fever, formally known as Oropouche virus disease or Oropouche fever, is caused by the Oropouche virus, an orthobunyavirus. This virus is distinct from flaviviruses (like dengue and Zika) and alphaviruses (like chikungunya). It was first identified in Trinidad and Tobago in 1955.

Symptoms of Oropouche virus include fever, severe headache, chills, muscle aches, joint pain, nausea, vomiting, and rash. Approximately 60% of infected individuals become ill, with most recovering in under a month. Severe complications, such as encephalitis and meningitis, can occur but are rare.

Current Outbreak Situation

In July 2024, the Pan American Health Organization issued a warning following the deaths of two women in Brazil linked to Oropouche virus. There have also been cases of miscarriage, fetal death, and microcephaly in newborns due to the virus, echoing the 2015–16 Zika outbreak. Although historically significant, Oropouche had faded in prominence after outbreaks of chikungunya, Zika, and dengue.

How is Oropouche Virus Spread?

The Oropouche virus is primarily transmitted by blood-feeding insects, particularly biting midges (Culicoides paraensis) and mosquitoes. It circulates in forested areas with non-human primates, sloths, and birds as potential hosts. During urban outbreaks, the virus spreads among humans through these insects.

Why is Oropouche Virus on the Rise?

Recent reports from the CDC highlight a rise in Oropouche virus cases beyond its traditional areas, such as the Amazon basin. Over 8,000 cases have been reported across Brazil, Bolivia, Peru, Colombia, and Cuba. Factors like climate change, deforestation, and increased human movement may contribute to the virus’s spread. Oropouche virus may also evolve faster than other viruses, potentially increasing its impact.

Should Australia Be Concerned?

Currently, the risk of Oropouche virus spreading to Australia is low. The biting midges that spread the virus in the Americas are not present in Australia. However, authorities should be vigilant for returning travelers and ensure appropriate testing protocols are in place. Australia has its own local orthobunyaviruses, but the health risks are considered low.

How Can Travelers Protect Themselves?

There is no vaccine or specific treatment for Oropouche virus. Travelers to South and Central America should take precautions to avoid mosquito and biting midge bites:

• Use insect repellents containing DEET, picaridin, or oil of lemon eucalyptus.
• Wear long-sleeved shirts, long pants, and covered shoes.
• Sleep under insecticide-treated mosquito nets with fine mesh to protect against smaller biting midges.

Pregnant travelers should consult healthcare professionals about travel plans and potential risks.

Keywords: Sloth fever, Oropouche virus, mosquito-borne diseases, travel health, South America, disease prevention