ON THE SILVER RIVER — Wildlife managers in Florida say they want to remove roaming monkeys from the state in light of a new study published Wednesday that finds some of the animals are excreting a virus that can be dangerous to humans.
Scientists studying a growing population of rhesus macaques in Silver Springs State Park in Ocala say that rather than just carrying herpes B, which is common in the species, some of the monkeys have the virus in their saliva and other bodily fluids, posing a potential risk of spreading the disease.
Human cases of the virus have been rare, with about 50 documented worldwide, and there have been no known transmissions of it to people from wild rhesus macaques in Florida or elsewhere. However, the researchers say the issue has not been thoroughly studied.
The findings, published in the Centers for Disease Control and Prevention journal Emerging Infectious Diseases, prompted the researchers from the universities of Florida and Washington to warn Florida's wildlife agency that the infected monkeys should be considered a public health concern.
State wildlife officials say they are taking the problem seriously.
"Without management action, the presence and continued expansion of non-native rhesus macaques in Florida can result in serious human health and safety risks including human injury and transmission of disease," Thomas Eason, assistant executive director of the Florida Fish and Wildlife Conservation Commission, said in a statement.
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Eason would not elaborate on what specific management tactics the state may employ, but a spokeswoman said the commission supports ridding the state of the invasive creatures.
"The commission supports the removal of these monkeys from the environment to help reduce the threat they pose. This can be done in a variety of ways," spokeswoman Carli Segelson said in an email.
The macaques, native to Asia, are one of Florida's many nonnative wildlife species. Their contacts with the public, including last summer when the monkeys chased a family , have made them somewhat notorious critters and have caused two partial park closures since 2016. The monkeys also have roamed far outside the park: Dozens were photographed recently swarming a deer feeder outside a home in Ocala. They have been spotted in trees in the Sarasota and Tallahassee areas.
The herpes B virus has been fatal to 21 of the 50 humans known to have contracted it from macaque bites and scratches while working with the animals in laboratories, according to the CDC.
The CDC said there is always concern about the threat that diseases like herpes B virus pose to people, especially in settings where there is frequent interaction between animals and humans where scratches or bites can occur.
"Herpes B virus infection is extremely rare in people, but when it does occur, it can result in severe brain damage or death if the patient is not treated immediately," CDC spokesman Ian Branam said in a statement.
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The researchers estimate that up to 30 percent of the scores of Florida's feral macaques may be actively excreting the virus.
The findings suggest a public health concern, said David Civitello, an Emory University biology professor who was not involved in the study. Still, he said, while the research confirms the presence of the virus in the monkeys' bodily secretions, more work needs to be done to establish how much virus there is, and how easily transferable it is.
"It is interesting to see oral shedding at all," Civitello said in an email after reviewing the paper. "It will be important to figure out whether underreporting, low quantities, or low transmissibility would explain why infections in tourists have not been reported."
The presence of the virus in the monkeys' feces and saliva presents issues for park workers and visitors, who could be endangered if bitten or scratched.
"Human visitors to the park are most likely to be exposed ... through contact with saliva from macaque bites and scratches or from contact with virus shed through urine and feces," the paper's authors wrote.
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The creatures draw nature lovers. On a chilly day in November, Capt. Tom O'Lenick, who has navigated the Silver River for 35 years, hollered from his charter boat into the dense surrounding forest. "Monkey, monkey, monkey!" he cried.
More than two dozen monkeys eventually appeared in trees on the riverbank. Within minutes, curious kayakers and other boat tour operators pulled close to shore for a better look and to snap photos.
Minutes later another troop was running along the opposite riverbank.
The animals' forebears were brought to an island in the Silver River early in the 1930s as a tourist attraction due to the popularity of the Tarzan movies.
But there was human error in that plan.
"They didn't know monkeys could swim," O'Lenick said. Now there are believed to be about 175 in Silver Springs State Park.
While there are no official statistics on monkey attacks on humans in the park, a state-sponsored study in the 1990s found 31 monkey-human incidents, with 23 resulting in human injury between 1977 and 1984.
Samantha Wisely, a University of Florida disease ecologist and one of the study's authors, said whether the monkeys pose a significant public health threat is still unknown. The paper recommends that Florida wildlife managers consider the virus in future policy decisions.
"We don't have any silver bullet; that's the nature of science," Wisely said.