Simian adenoviruses: Molecular and serological survey in monkeys and humans in Thailand

Simian adenoviruses are in the genus Mastadenovirus of the family Adenoviridae. This family is composed of non-enveloped, double-stranded DNA viruses that infect a wide range of animals. Mastadenoviruses infect mammals, including non-human primates and humans. The close genetic relatedness between simian and human adenoviruses, with its associated potential for the cross-species transmission of zoonotic adenoviruses from monkeys to humans and vice versa, poses important health concerns and thus warrants research. In this study, we performed a molecular survey of adenoviruses in monkeys in Thailand. Most of the monkeys tested here were long-tailed macaques, free-ranging in areas close to human territories across four provinces: Ratchaburi, Kanchanaburi, Lopburi, and Prachuap Khiri Khan. A few fecal samples from captive wild monkeys (a stump-tailed macaque, pig-tailed macaques, gibbons, and a leaf monkey) were also tested. Adenoviruses were detected in 33.3% (70 out of 210) of the fecal or rectal swab samples. The viruses identified in these samples included Simian adenovirus (SAdV)-A, SAdV-B, SAdV-H, Human adenovirus (HAdV)-D, HAdV-G, and a bat adenovirus species. One SAdV-B, SAdV RBR-7-10, was isolated from a long-tailed macaque fecal sample and identified by mass spectrometry. Its full hexon gene and nearly complete DNA polymerase gene were sequenced and analyzed, and the virions were imaged by transmission electron microscopy. The SAdV RBR-7-10 virus was used in a microneutralization assay to identify virus-specific antibodies in monkey plasma and human serum samples collected from the same areas in Prachuap Khiri Khan Province. We detected neutralizing antibodies against SAdV RBR-7-10 in 6.8% (n = 103) of the monkey samples but in none of the 125 human serum samples, suggesting no cross-species transmission of SAdV RBR-7-10 occurred at this study site. Nevertheless, a continuing surveillance of pathogens in monkeys is warranted to quickly identify possible emerging zoonotic outbreaks.