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Little is known about the ecology of influenza A virus (IAV) in nonhuman primates (NHPs). We conducted active surveillance of IAV among 672 cynomolgus macaques (Macaca fascicularis) living in 27 free-ranging colonies in Thailand between March and November 2019. A hemagglutination inhibition (HI) assay was employed as the screening test against 16 subtypes of avian influenza virus (AIV) and two strains of the H1 subtype of human influenza virus. The serum samples with HI titers ≥20 were further confirmed by microneutralization (MN) assay. Real-time RT-PCR assay was performed to detect the conserved region of the influenza matrix (M) gene. The seropositive rate for subtypes of IAV, including AIV H1 (1.6%, 11/672), AIV H2 (15.2%, 102/672), AIV H3 (0.3%, 2/672), AIV H9 (3.4%, 23/672), and human H1 (NP-045) (0.9%, 6/672), was demonstrated. We also found antibody against more than one subtype of IAV in 15 out of 128 positive tested sera (11.7%). Moreover, influenza genome could be detected in 1 out of 245 pool swab samples (0.41%). Evidence of IAV infection presented here emphasizes the role of NHPs in the ecology of the virus. Our findings highlight the need to further conduct a continuous active surveillance program in NHP populations. [ABSTRACT FROM AUTHOR]

The present study conducted a longitudinal serological survey and active surveillance for influenza virus in freeranging nonhuman primates (NHPs) in Thailand. One hundred and nine serum samples from NHPs were collected between 2009 and 2017, in 4 provinces of Thailand; while 282 oropharyngeal swabs were collected between April to August, 2018, in 8 provinces of Thailand. Our results demonstrated that no antibody to influenza virus was found in NHP sera by using blocking enzyme-linked immunosorbent (ELISA) assay and hemagglutination inhibition (HI) assay. Moreover, no influenza genome could be detected in all new NHP swab samples by using real-time RT-PCR assay. However, monitoring and surveying of influenza virus in these species should be maintained. [ABSTRACT FROM AUTHOR]