Serological insights into zoonotic viruses in urban long-tailed macaques: A case study from Bali

Zoonotic diseases like COVID-19 and Ebola highlight the rising risks linked to habitat degradation and intensified human-wildlife interactions. Primates closely related to humans can harbor zoonotic pathogens, such as yellow fever and malaria. This study examines the host potential of synanthropic long-tailed macaques (Macaca fascicularis) in a Bali tourist site, where frequent human-macaque interactions pose zoonotic risks, emphasizing the need to monitor pathogens for public health and conservation. Using ELISA-based analyses, 78 samples from 6 groups of macaques were tested in 2022 for zoonotic viruses: Norovirus GII4, Rotavirus, Measles morbillivirus, SARS-CoV-2, Herpes B, Japanese Encephalitis Virus (JEV), and Dengue. To assess the role of intrinsic host parameters on macaque infection risk, we investigated the influence of age, sex, and group membership on seropositivity for each virus. Surprisingly, none of these factors significantly influenced seropositivity. However, our study is the first to report the presence of Dengue virus, Norovirus, Rotavirus, and Measles morbillivirus in wild macaques in Indonesia. Regarding JEV, compared to a former study on the same population, we found that seropositivity decreased from 39% to 9% in 2022, likely due to population turnover or seasonal vector activity. The high Herpes B seroprevalence (95%) we found aligns with findings in similar settings. However, the absence of documented natural transmission of Herpes B from macaques to humans in natural settings is notable, but further investigation of this pathogen in wild populations is needed. The high seropositivity for Rotavirus (65%), potentially from human origin, underscores the risk of reverse zoonotic transmission, raising concerns for primate conservation. These findings emphasize the need to maintain surveillance in primates of touristic areas through a One Health approach to understand pathogen dynamics and mitigate zoonotic risks at human-primate interfaces.