High Prevalence of Highly Pathogenic Avian Influenza: A Virus in Vietnam's Live Bird Markets

Abstract

Background: In recent years, Vietnam has suffered multiple epizootics of influenza in poultry.

Methods: From 10 January 2019 to 26 April 2021, we employed a One Health influenza surveillance approach at live bird markets (LBMs) and swine farms in Northern Vietnam. When the COVID-19 pandemic permitted, each month, field teams collected oral secretion samples from poultry and pigs, animal facility bioaerosol and fecal samples, and animal worker nasal washes at 4 LBMs and 5 swine farms across 5 sites. Initially samples were screened with molecular assays followed by culture in embryonated eggs (poultry swabs) or Madin-Darby canine kidney cells (human or swine swabs).

Results: Many of the 3493 samples collected had either molecular or culture evidence for influenza A virus, including 314 (37.5%) of the 837 poultry oropharyngeal swabs, 144 (25.1%) of the 574 bioaerosol samples, 438 (34.9%) of the 1257 poultry fecal swab samples, and 16 (1.9%) of the 828 human nasal washes. Culturing poultry samples yielded 454 influenza A isolates, 83 of which were H5, and 70 (84.3%) of these were highly pathogenic. Additionally, a positive human sample had a H9N2 avian-like PB1 gene. In contrast, the prevalence of influenza A in the swine farms was much lower with only 6 (0.4%) of the 1700 total swine farm samples studied, having molecular evidence for influenza A virus.

Conclusions: This study suggests that Vietnam's LBMs continue to harbor high prevalences of avian influenza A viruses, including many highly pathogenic H5N6 strains, which will continue to threaten poultry and humans.

Keywords: avian influenza virus; highly pathogenic avian influenza virus; influenza virus; zoonosis; zoonotic influenza.

Figure 1.

Approximate geographical locations of live bird markets and swine farms studied in Northern Vietnam, 10 January 2019 to 26 April 2021.

Figure 2.

A neighbor-joining phylogenetic tree of the hemagglutinin (HA) gene segments of the isolated poultry H5N6 and H5N2 viruses and neuraminidase (NA) segments of isolated poultry H5N6 viruses. Red = HA and NA sequences from specimens collected in the Lang Son Province, Vietnam; green = HA and NA sequences from specimens collected in the Lao Cai Province, Vietnam; blue = HA and NA sequences from specimens collected in Hanoi, Vietnam; purple = HA and NA sequences from specimens collected in Quang Ninh Province, Vietnam; black = representative viruses from GenBank.

Figure 3.

A neighbor-joining phylogenetic tree of the neuraminidase (NA)(N2) gene segments of the isolated H5N2 poultry viruses collected in Lao Cai Province, Vietnam, compared to other representative HxN2 viruses from GenBank.

Figure 4.

A neighbor-joining phylogenetic tree of the hemagglutinin (HA) and neuraminidase (NA) gene segments of the isolated poultry H9N2 viruses. Red = HA and NA sequences from specimens collected in Lang Son Province, Vietnam; green = HA and NA sequences from specimens collected in Lao Cai Province, Vietnam; black = representative H9N2 viruses from GenBank.