A potentially deadly virus commonly known as "sloth fever" is sparking new pleas for caution across the United States after Florida reported nine new cases in a week related to international travel — a troubling sign as many Americans return from their summer vacations.
Spread by small biting flies and mosquitoes, sloth fever, or Oropouche fever, is caused by the Oropouche virus.
Earlier this month, the Pan American Health Organization (PAHO) put out an advisory warning of "highly concerning changes in the observed clinical and epidemiological characteristics" of the disease, including the recent increase and expansion of cases in newly recorded areas, outside the regions where Oropouche is previously considered to be endemic. More concerning have been the first-ever reports of deaths associated with sloth fever, and the identification of potential transmission of the disease contributing to fetal deaths or health problems at birth, officials say.
The risk to the Americas, including North and South America, where the disease has been spreading as of late, is considered to be high, according to PAHO. On the heels of the PAHO report, the Centers for Disease Control (CDC) and Prevention put out a note advising clinicians and public health authorities of the expanded threat. New York state health officials then disseminated that advisory to providers throughout the Empire State for awareness.
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According to the CDC, Oropouche virus gets introduced into urban environments from infected humans, who likely get the disease while visiting forested areas. The virus transmits from animals like sloths, hence the name, and rodents to mosquitoes and flies, who then transmit it to humans. There is no evidence of local transmission in the U.S., the CDC says. That said, biting midges and possibly certain mosquitoes can transmit the virus from an infected person to a non-infected person in urban areas, according to the CDC. Additional cases in the U.S. are expected, officials say.
Currently, the 2024 outbreak is occurring in endemic areas and new areas outside the Amazon basin, most notably Brazil, Bolivia, Peru, Columbia and Cuba, the CDC says.
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What are the symptoms of sloth fever?
Diagnosis has its challenges, because the clinical presentation is similar to diseases caused by other mosquito-borne viruses, like dengue and chikungunya.
According to the CDC, about 60% of people infected with Oropouche virus become symptomatic. The incubation period is typically 3 to 10 days.
Oropouche presents most often with acute onset of fever, chills, headache, muscle aches and joint pain. Eye pain, light sensitivity, nausea, vomiting, fatigue are also possible. Symptoms tend to resolve after a few days, the CDC says, but a vast share (70%) of people experience recurrent symptoms days to weeks after the initial symptoms resolve.
Although illness is typically mild, the CDC says less than 5% of patients can develop hemorrhages or neuroinvasive diseases like meningitis. Symptoms of the latter may include intense eye pain, dizziness, confusion and lethargy.
Although people exposed to infected biting midges or mosquitoes are most at risk for developing the disease, the CDC says the risk factors for more severe cases are not well-defined. People at risk for more severe disease likely include those at higher risk for other severe viral infections, like people aged 65 and older and those with underlying conditions. No specific antiviral treatments or vaccines are available. Treatment includes rest, fluids and pain meds.
So far this year, more than 8,000 cases of Oropouche virus have been confirmed in the five South American countries.
Florida has reported 20 travel-related cases of Oropouche virus this year, nine of which were reported last week. Thus far, one case has been reported in New York, according to the state health department's latest update.
