A Monkey Bite in Thailand and the Risk of Herpes B Virus

This page summarizes a "Notes from the Field" report in CDC's MMWR by the Oregon Public Health Division, Clackamas County Public Health, CDC and the National B Virus Resource Center, about an exposure in December 2018.

What happened

On December 24, 2018, an Oregon teenager was bitten by a macaque monkey in a public park in Phuket, Thailand. The bleeding wound was rinsed right away with bottled water, without soap, and hotel staff applied a topical pain reliever. The next day she went to a local clinic and got her first dose of rabies postexposure vaccine, though no rabies immune globulin, and had two more doses before leaving Thailand on January 5, 2019.

On January 7 an Oregon physician, asked when to give the final rabies dose, contacted the local health department, which in turn contacted the Oregon Public Health Division. Officials there were concerned about possible exposure to Macacine herpesvirus 1 (B virus).

Why B virus matters

B virus is common in macaques. In rare cases it causes severe encephalitis in people if not treated promptly, and untreated infection kills close to 80% of those infected. There is no vaccine.

The state contacted CDC and the National B Virus Resource Center in Atlanta about testing, and advised that if symptoms appeared (fever, chills, myalgia, headache, blisters or discomfort near the wound, or problems with coordination) the patient should seek care and the provider should notify the center at once. She received her last rabies dose on January 8, and blood samples taken that day and 3 weeks later, on January 29, were tested for B virus IgM and IgG antibodies. Neither was positive.

A negative test does not settle the matter. After exposure, too little virus may reach the blood to trigger antibodies, and B virus can travel to the dorsal ganglion and cause infection years later, establishing a lifelong latent infection. The patient was advised to always carry a Medical Alert card in case symptoms ever appear.

How rare is it?

• Symptomatic B virus infection in people is rare, though seroconversion in some people suggests silent infection can happen.
• Nearly all documented human infections came from exposures in laboratories or animal facilities. Transmission from macaques to people in public places such as parks has not been documented.
• Still, macaques in such settings often carry B virus and can shed it without symptoms. The macaque here ran off and could not be tested.

The risk from macaques in public settings is considered low, but the consequences are severe enough that precautions are warranted, especially for bites and scratches.

What to do

• Avoid close contact with free-ranging macaques.
• After a bite or scratch, scrub the wound with soap, detergent or iodine for 15 minutes, then rinse under running water for another 15–20 minutes, and seek medical care right away. Treatment depends on the details of the incident.
• Rabies. Rabies from primate bites is uncommon because primates are not main rabies reservoirs, but postexposure prophylaxis should be considered after a primate bite in countries where rabies is enzootic.

Sources

• Wu AC, Rekant SI, Baca ER, et al. "Notes from the Field: Monkey Bite in a Public Park and Possible Exposure to Herpes B Virus — Thailand, 2018." MMWR 69(9). https://www.cdc.gov/mmwr/volumes/69/wr/mm6909a6.htm
• CDC, B virus first aid and treatment: https://www.cdc.gov/herpesbvirus/firstaid-treatment.html
• The report's photograph is not reproduced, because the report was prepared jointly with Oregon health agencies and Georgia State University's National B Virus Resource Center.