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Rhesus macaques in Florida expose parkgoers to deadly virus

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January 13, 2018

Image of rhesus macaque
Researchers warn that rhesus macaques in Florida can transmit McHV-1 to humans.

Researchers have found evidence that people visiting a popular public park in Florida are at risk for contracting a potentially deadly virus known as macacine herpesvirus 1, or herpes B virus, through contact with rhesus macaques.

In light of this new evidence, Florida Fish and Wildlife Conservation Commission (FWC) officials are considering removing the animals, which roam freely in the area and are frequently fed by visitors.

“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 H. Eason, PhD, FWC Assistant Executive Director, said in a statement. “Additionally, macaques can negatively impact Florida native wildlife and pose potential risks to agriculture and recreation. Therefore, the FWC supports active management to remove these threats.”

Macacine herpesvirus 1 (McHV-1) is typically transmitted to humans through exposure to macaque bodily fluids, including bites and scratches, according to Samantha M. Wisely, PhD, associate professor at the University of Florida, Gainesville, and Institute of Food and Agricultural Sciences, and colleagues. Rhesus macaques that harbor McHV-1 can shed the virus from oral, nasal or genital mucosa during periods of stress.

Photo of Samantha Wisely
Samantha M. Wisely

“Although the infection does not produce clinical illness in macaques, [approximately] 50% of infections cause fatal encephalitis in humans if left untreated,” the researchers wrote in Emerging Infectious Diseases.

All known cases and deaths caused by McHV-1 in humans are linked to captive animals in laboratory settings, according to the researchers. Rhesus macaques are considered an occupational health threat to laboratory workers. However, little is known about the risk for transmission outside of the laboratory setting.  

Rhesus macaques were first introduced into Silver Springs State Park in the 1930s as an attempt to increase tourism, the researchers noted. About 175 macaques were living in the park in 2015.

Wisely and colleagues collected saliva and feces samples from rhesus macaques in the Sliver Springs State Park in the fall of 2015 and spring and summer of 2016 to determine the frequency of viral shedding in the animals. The macaques belonged to social groups that are most habituated to people. The researchers also analyzed blood samples that were obtained from 317 rhesus macaques in the Marion County, Florida, region from 2000 to 2012.

From 2000 to 2012, the percentage of rhesus macaques with McHV-1 antibodies was 25%, indicating they are carriers of the virus, according to Wisely. In 2015, the percentage of rhesus macaques shedding virus ranged from 4% (95% CI, 1%-4%) to 14% (95% CI, 5%-35%). There was no evidence of viral shedding in the spring or summer of 2016, nor was there evidence of shedding in feces. The virus was detected only in saliva samples during the fall, which is the animals’ breeding season and a particularly stressful time of year, according to the researchers.

“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,” Wisely and colleagues warned.

However, because there have been no reports of McHV-1 transmission from wild macaques to humans, the exact threat that the animals pose remains unclear, according to Wisely. The researchers’ next phase of investigation, she said, is to determine whether McHV-1 strains differ among captive and wild rhesus macaques. 

“These macaques are spread all over the globe. There has to be hundreds of thousands, if not millions, of human-monkey interactions that occur,” Wisely told Infectious Disease News. “The risk for contracting the virus is probably really low, but if you get it, the consequences are extremely dire. People should always have an abundance of caution when near wildlife to reduce the risk for infection.”– by Stephanie Viguers

Disclosures: Wisely reports no relevant financial disclosures.