Neutralizing antibody evidence of dengue and chikungunya virus exposure in macaques from an urban-forest fringe in Peninsular Malaysia.

Arboviruses such as dengue virus (DENV), chikungunya virus (CHIKV), Zika virus (ZIKV), and Japanese encephalitis virus (JEV) circulate between mosquito vectors and vertebrate hosts, with non-human primates (NHPs) playing an important role in sylvatic transmission cycles. In Malaysia, frequent interactions between long-tailed macaques (Macaca fascicularis) and humans at the Universiti Kebangsaan Malaysia (UKM) Bangi campus provide an opportunity to investigate arbovirus exposure at the human-wildlife interface. Forty free-ranging macaques were sampled from five locations within the UKM Bangi campus. Serum samples were screened for neutralizing antibodies against DENV, CHIKV, ZIKV, and JEV using the 90% focus reduction neutralization test (FRNT90), while whole blood was tested for viral RNA by RT-qPCR. Seventeen macaques (42.5%) had neutralizing antibodies, indicating previous arbovirus exposure. Specifically, 16 (40.0%) had neutralizing antibodies against DENV and one (2.5%) against CHIKV. Neutralizing antibodies against DENV-1, DENV-2, and DENV-3 were detected, whereas DENV-4, ZIKV, and JEV antibodies were not detected. No viral RNA was identified in any sample. To our knowledge, this is the first study in Malaysia to investigate arbovirus exposure in free-ranging macaques using FRNT90 neutralizing antibody assays. These findings provide updated evidence of DENV and CHIKV exposure in macaques at the human-wildlife interface and highlight the need for integrated longitudinal surveillance of NHPs, mosquito vectors, and humans to better understand arbovirus ecology and transmission dynamics.