Prevalence of Herpes B Virus in Wild Long-Tailed Macaques, Thailand, 2018–2024

Herpes B virus (B virus) is an enigmatic zoonotic virus that has caused severe neurologic symptoms in humans exposed to captive macaques used for experimentation. We examined 864 wild long-tailed macaques from 22 locations across Thailand for B virus infection. All 22 macaque populations tested positive for B virus antibodies; seropositivity ranged from 25% to 100%. B virus shedding was detected in 9 (1.04%) oral swab samples by using quantitative PCR of the virus UL29 gene. We phylogenetically analyzed partial genome sequences of B virus (US5-US6 genes) from 6 of the PCR-positive samples. All 6 sequences were clustered in clade II, which includes B virus strains from rhesus, Japanese, and long-tailed macaques, suggesting co-evolution of B virus with macaques. Continued surveillance and sequencing of B virus in macaque populations will be needed to prevent B virus transmission to humans and to develop appropriate vaccines to prevent human B virus infections.