Poster #27 - One Health surveillance for influenza A viruses in Vietnamese live bird markets from January 2019 to April 2021

Tung D. Dao, Coleman, K.K., Vuong N. Bui, Anh N. Bui, Long H. Tran, Quy D. Nguyen, Son T. Than, Pulscher, L.A., Marushchak, L.V., Robie, E.R., Hung Nguyen-Viet, Phuc Pham-Duc, Christy, N.C., Brooks, J.S., Huy C. Nguyen, Rubrum, A., Webby, R.J. and Gray, G.C. 2025. Poster #27 - One Health surveillance for influenza A viruses in Vietnamese live bird markets from January 2019 to April 2021. One Health 20: 100822.

Background: The recent detections of H5N1 viruses among avian and mammalian species worldwide highlight the panzootic nature of influenza A viruses. There is specific concern that some influenza A viruses, such as H5N1, which are more generalist in nature and may be more prone to crossing the species barrier, causing disease in humans. Active surveillance for influenza A viruses among poultry, humans, and their shared environment is paramount to understanding their transmission potential and provides information on currently circulating avian strains.

Purpose: In this study, we employed a One Health approach for the surveillance of influenza A viruses in Vietnamese live bird markets.

Methods: Over a two-year period, oropharyngeal and environmental fecal swabs from birds, nasal washes from poultry market workers, and bioaerosol samples were prospectively collected monthly at four live bird markets in Vietnam in 5 provinces including Lang Son, Lao Cai and Quang Ninh that share the border with China, and Hanoi city. Influenza A viruses were studied using qRT-PCR and cell or egg culture, followed by Sanger sequencing for positive cases.

Findings: Among the 3493 samples collected, 37.5% (n = 314) of oropharyngeal swabs, 34.9% (n = 438) of fecal swabs, 25.1% (n = 144) of bioaerosol samples, and 1.9% (n = 16) of the human samples had evidence of influenza A viruses by qRT-PCR or egg culture. Of the poultry and environmental (fecal and bioaerosol) isolates tested, 83 (18.3%) had evidence of H5 influenza viruses and 70 (84.3%) of these were characterized as highly pathogenic avian influenza, including H5N2 and H5N6 strains. Of the human samples tested, one sample returned good Sanger sequence results for the PB1 gene. Phylogenetic analysis of this sample showed clustering with PB1 genes from H9N2 viruses isolated from chickens and ducks in Vietnam.

Conclusion: Together these data suggest that Vietnamese live bird markets continue to have a high prevalence of influenza A viruses circulating, many of which are highly pathogenic A/H5 strains. Additionally, the identification of an H9N2 avian-like PB1 gene in a poultry market worker suggests avian influenza viruses may be spilling over into the human population. These results set the stage for continued One Health surveillance for influenza A viruses in live bird markets to identify currently circulating strains and better understand the potential for cross-species transmission of such viruses to humans.