IPSF: H5N2 and H7N3 in Mexico

8 July 2026

1 minute read

By: Chris Wright

Editor's note: The following are excerpts of a poster presentation by Inkar Castellanos-Huerta and colleagues at the University of Arkansas, USA; Northwest Arkansas Community College, USA, and the Universidad Autónoma de Querétaro, Mexico, during the 2026 International Poultry Scientific Forum.

The influenza A virus is considered a significant agent due to its substantial socio-economic and eco-epidemiological impact, stemming from its ability to circulate in diverse species, where it can cross interspecies barriers and infect other hosts, demonstrating its high zoonotic potential. 

In Mexico, the avian influenza virus first appeared in 1994 with the H5N2 subtype, and later in the 20th century, the H7N3 subtype emerged. It is well established that migratory waterfowl facilitate the transmission and persistence of the virus in the national poultry population. 

This research evaluated the evolutionary dynamics over time and space of highly pathogenic avian influenza (HPAI) strains in relation to strains circulating in wild bird populations in the Americas, comparing them with recent isolates from wild birds to establish the evolutionary relationships between viruses of wild and domestic origin circulating in the country. 

Fifteen H5N2 strains, thirteen H7N3 strains, and one Mexican wild-origin strain, which differ from each other based on their spatiotemporal dynamics, were evaluated to determine evolutionary relationships using phylogenetic inference analysis. 

Phylogenetic trees were constructed by applying discrete trait variables to develop inference networks and perform discrete spatiotemporal diffusion analysis using geospatial software. Phylogenetic inference established that the Mexican lineage originated primarily from intraspecific diffusion of wild origin; however, it has not developed an evolutionary network with wild viruses circulating in the country. Domestic populations have been the focus of regional geographic persistence, continental genomic diffusion, genomic variability, and interspecies transmission, especially to mammals. 

Based on the results of this study, it is established that poultry production in Mexico plays a significant ecological role in the circulation of the avian influenza virus, and that wild birds play a crucial ecological role in the geographic dispersal of the virus. Still, domestic populations promote regional and continental genomic persistence and dynamism.