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. 2023 Dec;17(12):e13245.
doi: 10.1111/irv.13245.

Avian influenza A(H5) virus circulation in live bird markets in Vietnam, 2017-2022

Diep T Nguyen  1 , Kelsey M Sumner  2   3 , Thoa T M Nguyen  2 , Minh Q Phan  1 , Tien M Hoang  1 , Chuong D Vo  1 , Tho D Nguyen  4 , Phuong T Nguyen  5 , Genyan Yang  2 , Yunho Jang  2 , Joyce Jones  2 , Sonja J Olsen  2 , Philip L Gould  2 , Long V Nguyen  1 , Charles Todd Davis  2
Affiliations

Avian influenza A(H5) virus circulation in live bird markets in Vietnam, 2017-2022

Diep T Nguyen et al. Influenza Other Respir Viruses. 2023 Dec.

Abstract

Background: Highly pathogenic avian influenza A(H5) human infections are a global concern, with many A(H5) human cases detected in Vietnam, including a case in October 2022. Using avian influenza virus surveillance from March 2017-September 2022, we described the percent of pooled samples that were positive for avian influenza A, A(H5), A(H5N1), A(H5N6), and A(H5N8) viruses in live bird markets (LBMs) in Vietnam.

Methods: Monthly at each LBM, 30 poultry oropharyngeal swab specimens and five environmental samples were collected. Samples were pooled in groups of five and tested for influenza A, A(H5), A(H5N1), A(H5N6), and A(H5N8) viruses by real-time reverse-transcription polymerase chain reaction. Trends in the percent of pooled samples that were positive for avian influenza were summarized by LBM characteristics and time and compared with the number of passively detected avian influenza outbreaks using Spearman's rank correlation.

Results: A total of 25,774 pooled samples were collected through active surveillance at 167 LBMs in 24 provinces; 36.9% of pooled samples were positive for influenza A, 3.6% A(H5), 1.9% A(H5N1), 1.1% A(H5N6), and 0.2% A(H5N8). Influenza A(H5) viruses were identified January-December and at least once in 91.7% of sampled provinces. In 246 A(H5) outbreaks in poultry; 20.3% were influenza A(H5N1), 60.2% A(H5N6), and 19.5% A(H5N8); outbreaks did not correlate with active surveillance.

Conclusions: In Vietnam, influenza A(H5) viruses were detected by active surveillance in LBMs year-round and in most provinces sampled. In addition to outbreak reporting, active surveillance for A(H5) viruses in settings with high potential for animal-to-human spillover can provide situational awareness.

Keywords: Vietnam; avian influenza; live bird markets; poultry; surveillance.

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Conflict of interest statement

All authors report no conflicts of interest to declare.

Figures

FIGURE 1
FIGURE 1
Temporal distribution of influenza A(H5) viruses detected in live bird markets within each region. The numbers of samples that were tested in each province each month for influenza A and used as the denominator for A(H5) monthly percent positivity are indicated by the colored bars. The colors of the bars represent the overall region of Vietnam where red indicates the Northern region, orange the Central region, and yellow the Southern region. Monthly influenza A(H5) percent positivity within each region and year is indicated by the black lines. The bottom row indicates the mean monthly A(H5) percent positivity and corresponding 95% confidence interval within each region, averaging across all 6 years.
FIGURE 2
FIGURE 2
Temporal distribution of influenza A(H5N1), A(H5N6), and A(H5N8) viruses detected in three regions of Vietnam. (A) Monthly percent positivity of influenza samples that were confirmed as positive for influenza A(H5N1), A(H5N6), or A(H5N8) by rRT‐PCR and collected through active surveillance for avian influenza in live bird markets. Shaded areas indicate lack of surveillance activity. (B) Outbreaks of influenza A(H5N1), A(H5N6), and A(H5N8) reported to the Vietnam Department of Animal Health each month.
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