LONG-TERM SURVEILLANCE OF LANGUR ALPHAHERPESVIRUS IN A ZOO POPULATION OF SILVERED LANGURS (TRACHYPITHECUS CRISTATUS)

Langur alphaherpesvirus (HVL), a provisionally named alphaherpesvirus in the Simplexvirus genus, was first identified in 1991 at the Bronx Zoo in wild-origin silvered langurs (Trachypithecus cristatus) and their descendants. HVL is closely related to B virus (Macacine alphaherpesvirus 1) based on serologic and genetic data, but its natural history and zoonotic potential remain unknown. A cohort study was undertaken to describe the epidemiology, clinical impact, and potential management implications of this virus in a naturally infected, zoo-based population of silvered langurs. Opportunistic surveillance sampling from 1991 through 2015 resulted in 235 serum samples and 225 mucosal swabs from 75 individuals. A total of 43 individuals (57.3%) were seropositive for HVL within this period. Seroprevalence increased significantly with age, and indirect evidence suggested a peak in transmission at the onset of sexual maturity. These findings were similar to the behavior of other simplexviruses in their adapted hosts. Yearly cumulative incidence declined significantly through the study period, with zero or one new case detected each year from 2007 through 2015. The density of this population decreased within the study period for management reasons unrelated to HVL infection, and a change in age distribution or less-frequent contacts may have contributed to low transmission. In addition, clinical signs of simplexvirus infection were rare, and virus isolation was negative on all mucosal swabs, suggesting that viral shedding was infrequent. Yearly period seroprevalence remained relatively constant with a median of 45.8%, likely because of the extended survival of infected individuals within the population. Maintenance of a naturally occurring, novel virus with unknown zoonotic potential in a zoo population for over 25 yr highlights the importance of biosecurity and biosafety for management of silvered langurs and all primate species.