They have a herpes virus that can be fatal to humans. And their population could double by 2022.

“They” are a group of about 200 feral monkeys — rhesus macaques, to be exact — in Florida’s Silver Springs State Park. There is also a colony in Puerto Rico.

A 2018 report by the Centers for Disease Control and Prevention said researchers found that these rhesus macaques can shed the herpes B virus, known as macacine herpesvirus 1 or McHV-1, and this puts “humans at risk for exposure to this potentially fatal pathogen.”

No humans recently have contracted the virus, which is transmitted by bites, scratches and simian bodily fluids. For these reasons, the CDC issued a warning that officials should work on plans to limit the transmission of McHV-1.

“It’s going to be a problem. Continual growth of that population is going to occur without intervention,” University of Florida professor Steve Johnson said.

Johnson was part of a team of UF researchers that published the study of the monkeys over a nearly 15-year period starting in 2000 and reported by the CDC last year. The researchers analyzed blood and saliva from 317 of the monkeys and found that 25 percent of the population carried the virus and between 4 to 14 percent of the infected “were actively shedding the virus during the stressful fall mating season of 2015.”

The infection doesn’t produce clinical illness in macaques, but about 50 percent of the infections could cause fatal encephalitis in humans if left untreated, the UF study found. Researchers have documented 50 cases of the monkey B virus spreading to humans, with 21 of these proving fatal since the virus was identified in 1932. The risk of transmission is low, but the CDC noted: “Immunologic surveillance, reporting and diagnostic investigations in humans are lacking.”

For humans, untreated monkey B virus can feel like the flu, the CDC said, but could progress neurologically and have symptoms such as double vision and, later, paralysis and potential death.

The Journal of Wildlife Management noted that efforts to reduce the population hasn’t been easy because park visitors like seeing the monkeys, which are considered invasive. “They’re really charismatic and the public really likes them, so they’re really hard to manage,” lead author C. Jane Anderson said.