Influenza A(H5N1) Virus Clade 2.3.2.1a in Traveler Returning to Australia from India, 2024

Abstract

We report highly pathogenic avian influenza A(H5N1) virus clade 2.3.2.1a in a child traveler returning to Australia from India. The virus was a previously unreported reassortant consisting of clade 2.3.2.1a, 2.3.4.4b, and wild bird low pathogenicity avian influenza gene segments. These findings highlight surveillance gaps in South Asia.

Keywords: Australia; H5N1; India; avian influenza; highly pathogenic; human; influenza; respiratory infections; traveler; viruses.

Figure 1

Evolutionary origins of isolate A/Victoria/149/2024(H5N1) (red circles and bold text) in study of influenza A(H5N1) virus clade 2.3.2.1a in traveler returning to Australia from India, 2024. A) Reassortant origins of A/Victoria/149/2024 based on analysis of each segment; detailed phylogenies for all segments are provided in Appendix Figure 1). B–D) Maximum-likelihood trees for HA (B), PB2 (C), and M (D) genes with a sample of BLAST-matched sequences (https://blast.ncbi.nlm.nih.gov). Bootstrap values >90% for key nodes are shown. Scale bars indicate number of nucleotide substitutions per site for each gene. HA, hemagglutinin; LPAI, low pathogenicity avian influenza; M, matrix protein; NP, nucleoprotein; NS, nonstructural; PA, polymerase acidic; PB1, polymerase basic 1; PB2, polymerase basic 2.

Figure 2

Numbers and diversity of highly pathogenic avian influenza A(H5Nx) virus isolates reported in South and East Asia in GISAID (https://www.gisaid.org) during January 1, 2020–July 29, 2024. Pie charts for India and Bangladesh, the only 2 countries in which clade 2.3.2.1a hemagglutinin sequences (light green, arrow) have been deposited into GISAID, have been enlarged.