“Sloth Virus (Oropouche): Symptoms, Spread, and What’s New”

A weird virus that was previously exclusive to the Amazon is now spreading throughout America and may have become more potent as a result of genetic alterations.



Up until recently, the Oropouche virus was a relatively unknown disease that was primarily found in the Amazon Basin of South America. However, the virus has begun to spread outside of its usual territory as of late 2023. Thus far in 2024, over 8,000 instances have been reported across five countries; this illness is also referred to as “sloth fever.” The virus may have killed two unborn children in Brazil in addition to the two mothers who have lately died from it.

The number of oropouche cases spread by bug bites is rapidly rising, which is why the U.S. Centers for Disease Control and Prevention (CDC) have sent out a health advisory to doctors nationwide. In June and July of 2024, visitors from Brazil and Cuba were the first in Europe to report having contracted the illness.

So what is this mysterious virus exactly, where did it come from, and why should we be concerned about it?



What is Oropouche Virus?


In the South American Amazon, bites from insects carry the Orophouche endemic virus. Numerous species, including sloths, marmosets, and howler monkeys, have it, and it causes fever-like symptoms in people.

How does the virus spread?

The virus spreads through mosquito bites, which can occur in humans or animals. The disease is believed to be mostly carried by the pinhead-sized midge species *Culicoides paraensis*, which is common throughout the Americas. However, it can also be spread by mosquito bites from *Culex quinquefasciatus* and *Ochlerotatus serratus*. There isn’t any proof of direct human-to-human transmission to date.

After entering the bloodstream, the virus can swiftly spread throughout the body by breaching the blood-brain barrier and entering the central nervous system. It appears to focus primarily in the brain and liver.

The virus is made up of a single RNA strand that is protected from harm by a protein sheath. It’s thought to operate like a “Trojan horse” in the bloodstream, entering through immune cells called phagocytes, which enable it to travel unnoticed to various organs and tissues where it multiplies and infects cells.

Where Did Oropouche Come From?

The virus’s name pays tribute to the location of the initial case report. In the town of Vega de Oropouche, Trinidad and Tobago, a 24-year-old forest worker developed a fever in 1955, and it was found that the worker had the virus in his blood. Up to 100,000 cases have been documented in the Brazilian Amazon as a result of its sporadic outbreaks since then. In total, researchers estimate that there are over 500,000 cases; however, as many symptoms are similar to those of other illnesses that produce fever, this number may be overstated due to false positives.

Reports of epidemics in Ecuador, Peru, and Panama have surfaced since the late eighties. Bolivia, Ecuador, Colombia, and French Guiana are among the countries where instances of the virus have been reported since 2000.

What Caused the Most Recent Epidemic?

In the Amazon Basin, where the virus was already prevalent, and in other regions of South America, large outbreaks began towards the end of 2023. In June 2024, cases of the virus were detected in Cuba. Between January 1, 2024, and July 20, 2024, 8,078 cases of Oropouche were reported to the World Health Organization. Brazil reported the bulk of instances (7,284, including two fatalities); Bolivia recorded 356 cases, Peru 290, Colombia 74, and Cuba 74.

For public health experts, the most concerning trend is the rising number of cases in non-Amazonian regions, such as ten states in Brazil and Cuba that are not part of the Amazon. Recent, unpublished research have shown that the virus has undergone genetic modifications that may allow it to replicate more efficiently in infected cells. This could be a sign of a more severe disease and an increased risk of virus transmission through insect bites.

The virus can conceal itself among immune cells, which allows it to evade the body’s defenses, although there are hints that it may be more immune-stimulating from previous infections. Furthermore, scientists believe that one possible contributing cause to the recent epidemics is urbanization in formerly forested areas. Because of how climate change is affecting the areas where virus-carrying insects may live, the virus might continue to spread outside of its original range in South America.

Which Symptoms Are Present in Oropouche?



The virus causes a flu-like fever that includes headache, nausea, chills, stiff joints, painful muscles, and vomiting in infected individuals. Severe circumstances may arise from meningitis. The symptoms are generally similar to those of other mosquito-borne diseases such dengue, chikungunya, malaria, and Zika.

The symptoms often start to show up three to ten days after the bite and last for three to six days, as stated by the CDC. A few days or weeks later, symptoms can reappear in about 60% of patients, with comparable signs and symptoms after a recurrence. The reason for these relapses is unknown; it could be re-infection from high-transmission areas or the return of the same sickness.

How Serious Is Oropouche Fever?



On July 25, Brazil announced the first deaths linked to Oropouche fever. The two women who died were 21 and 24 years old, and there were no known medical conditions affecting them. A study conducted by the Brazilian Health Ministry found indications of a connection between Oropouche infection and stillbirths and miscarriages, suggesting that the virus may potentially infect fetuses during pregnancy. Additionally, the virus may have been the cause of four cases of newborns with microcephaly, a birth defect in which the baby’s head is smaller than usual. However, research on oropouche’s effects on pregnancy and fetuses is ongoing and results are preliminary.

Why Is It Called “Sloth Fever”?

The virus was first discovered in howler monkeys, but in 1960 it was also isolated from yellow-throated sloths in Brazil. However, the primary wild host of the virus is still unclear. It has been demonstrated that the virus is present in a wide variety of wild animals, including other primates and three-toed sloths. Many more wild species are suspected of being virus carriers, even if the main host of the virus is yet unknown.


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