Human Infection with Avian Influenza A(H9N2) Virus, Vietnam, April 2024

Abstract

In April 2024, Vietnam confirmed its first human case of influenza A(H9N2) in a 37-year-old man, marking a critical point in regional infectious disease monitoring and response. This case underscores the importance of robust surveillance systems and One Health collaboration in managing emerging zoonotic threats.

Keywords: H9N2; Keywords: influenza; One Health; Vietnam; avian influenza; respiratory infections; viruses; whole-genome sequencing; zoonoses.

Figure 1

Phylogenetic tree of the hemagglutinin gene of human influenza A(H9N2) virus isolated in Vietnam (bold text) and reference sequences, constructed using the maximum-likelihood method and Tamura-Nei model. The bootstrap consensus tree inferred from 1,000 replicates represents the evolutionary history of the taxa analyzed. Branches corresponding to partitions reproduced in <50% bootstrap replicates are collapsed. We obtained initial trees for the heuristic search automatically by applying neighbor-joining and BioNJ algorithms to a matrix of pairwise distances estimated using the Tamura-Nei model and then selecting the topology with superior log likelihood value. This analysis involved 37 nt sequences; codon positions included were first + second + third + noncoding, for a total of 1,773 positions in the final dataset. Evolutionary analyses were conducted in MEGA 11 (https://www.megasoftware.net). Scale bar represents 0.8 nucleotide substitutions per site.

Figure 2

Phylogenetic tree of the neuraminidase gene of human influenza A(H9N2) virus isolated in Vietnam (bold text) and reference sequences, constructed using the maximum-likelihood method and Tamura-Nei model. The bootstrap consensus tree inferred from 1,000 replicates represents the evolutionary history of the taxa analyzed. Branches corresponding to partitions reproduced in <50% bootstrap replicates are collapsed. We obtained initial trees for the heuristic search automatically by applying neighbor-joining and BioNJ algorithms to a matrix of pairwise distances estimated using the Tamura-Nei model and then selecting the topology with superior log likelihood value. This analysis involved 37 nt sequences; codon positions included were first + second + third + noncoding, for a total of 1,524 positions in the final dataset. Evolutionary analyses were conducted in MEGA 11 (https://www.megasoftware.net). Scale bar represents 0.8 nucleotide substitutions per site.