Rhesus Macaques in Florida Park Threaten to Spread Herpes B to Humans

Florida wildlife officials were given a reason to remove free-ranging rhesus macaques from a popular park in Marion County, due to new research finding that the monkeys are harboring a virus that can be deadly if contracted by humans: herpes B.

The study, published this week in the journal Emerging Infectious Diseases, looked at macaques residing in Silver Springs State Park. The investigators concluded that these macaques can shed the virus, thus, putting humans at risk for exposure.

“In laboratory settings, rhesus macaques are considered an occupational health threat because they harbor herpes B virus. Although the infection does not produce clinical illness in macaques, ~50% of infections cause fatal encephalitis in humans if left untreated,” they write.

The most typical form of transmission is when humans come into contact with bodily fluids of macaques harboring the virus—this can occur through bites and scratches. However, the investigators note that at least 1 instance of the virus being transmitted from human-to-human contact has been documented. Outside of the laboratory setting, investigators report that not much is known about the risk for transmission or the incidence of human disease resulting from herpes B exposure. The good news is, no human deaths associated with the virus have been reported, which suggests that risk of transmission is not very high.

Introduced to the park in the 1930s in an effort to draw tourists, the macaques were first detected to be producing herpes B antibodies in 1992. A total of 12 out of 29 macaques tested were seropositive.

“During 1984-2012, ~1000 animals were removed intermittently by permit-holding private trappers, but the practice of animal trapping has ended because of public controversy,” the authors write. Furthermore, no population management plans have been put in place to address the issue, at least as of December 12, 2017.

According to the study, the investigators found 2 genotypes of herpes B virus “that varied by a single amino acid change. Both of these genotypes have been found in laboratory populations, suggesting that >2 different laboratory-like strains circulate in the park population of macaques.” However, they only observed the macaques shedding the virus during the breeding season in the fall.

At least 23 documented bites occurred during human-macaque interactions between 1977-1984; however, the investigators posit that this rate is likely an underestimation and that more bites and scratches probably happen on a yearly basis, particularly because boaters on the Silver River are known to feed the animals at close distances.

“This human behavior probably exacerbates the public health threat of the rhesus macaque population to park visitors because incidents of negative human-macaque interactions increase when macaques are fed by humans,” the authors write. In fact, the park had to close on several occasions during 2016 and 2017 because macaques were exhibiting aggressive behavior.

“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. We have shown evidence of viral shedding of herpes B in free-ranging macaques at the popular public park, Silver Springs State Park. Although shedding rates appear lower than in captive settings, the potential for human-macaque contact in this park is high,” the authors conclude. “As of December 12, 2017, no evidence of human transmission from free-ranging macaques to humans exists. However, this pathogen should be considered a low-incidence, high-consequence risk, and adequate public health measures should be taken.”