Feral macaques in Florida pose herpes B risk to humans

Feral rhesus macaques living in a Florida state park can transmit herpes B virus, which is potentially deadly in humans.

Transmission is a low-incidence, high-consequence risk, according to an article in the February issue of Emerging Infectious Diseases.

About 175 rhesus macaques, many of them acclimated to humans, lived within Silver Springs State Park as of 2015, the article states. The park is in north-central Florida between the city of Ocala and Ocala National Forest.

Macaques harbor the herpes B virus, or macacine herpesvirus 1, without having clinical signs. In humans, half of untreated infections cause fatal encephalitis.

After initial infection, macaques acquire latent infections. They are more likely to shed the virus when stressed, such as when aggression increases among males during the fall mating season.

Researchers from the University of Florida and University of Washington tested 317 blood samples that were collected by private trappers—unrelated to the study—from 2000-12. Eighty-four—or about one-quarter—were seropositive for the herpes B virus.

The article authors wrote that prevalence likely is higher in the wild population. People with state-issued trapping permits tended, at least in the later years, to target younger monkeys that were less likely to be seropositive.

The researchers also collected 121 saliva samples and 23 fecal samples from two social groups of macaques­ during times of stress: mating, gestation, and lactation periods. The researchers watched macaques chew and discard swabs soaked in sucrose solution, but they were unable to determine which macaques deposited saliva on some samples.

Three swab specimens collected during the fall 2015 mating season were positive for herpes B virus, and the research team estimated the range in numbers of animals sampled.

The researchers determined that 4 to 14 percent of macaques were shedding the virus during the mating season.

"Although the potential for transmission of virus to humans clearly exists in Silver Springs State Park, no human infections or deaths caused by McHV-1 from free-ranging animals have been reported, despite frequent human-macaque interactions among many macaque populations worldwide," the article states. "All documented cases of human contraction of and death from McHV-1 have been associated with captive animals within laboratory settings."

The authors wrote that macaque-transmitted herpes B virus infection in humans may be misdiagnosed and underreported. The etiology of encephalitis is undetermined in 30 to 60 percent of U.S. cases because of the rapid onset of nonspecific disease, transient nature of the viremia, and lack of rapid and specific diagnostic tests, the article states.

Nobody has reported contracting the virus from monkeys, but people have had violent encounters. State wildlife authorities received 23 reports of macaques biting people from 1977-84 in or near the state park.

"Given the current information available, we must consider the presence of the population of invasive rhesus macaques in Florida to be a public health concern," the article states.

Trappers removed about 1,000 monkeys from 1984-2012, bringing the population down from a peak of about 400. Public dispute over trapping ended the trapping program, and the state lacked population management plans as of December 2017.

The 2002 book "Primates Face to Face: Conservation Implications of Human-Nonhuman Primate Interactions" indicates the macaques may have originally been released in two batches between the mid-1930s and late 1940s by a glass-bottom boat tour company owner who wanted to increase excitement for a "jungle" cruise.

The EID article is available at http://jav.ma/EIDmacaques.