Second Human Case of Avian Influenza A(H5N2) Confirmed in Mexico
Mexican health authorities have confirmed that a human infection reported on 30 September 2025, initially classified as avian influenza A(H5), was identified as avian influenza A(H5N2). This represents the country’s second documented human case of H5N2. The first confirmed human infection with avian influenza A(H5N2) was reported on 23 May 2024 in a 59-year-old resident of the State of Mexico, who was hospitalized in Mexico City. The patient had no known exposure to poultry or other animals and died from the infection. That event marked the first laboratory-confirmed human case of H5N2 globally and the first recorded human infection with an avian H5 virus in Mexico.
The sequenced strain of the second case, A/Mexico City/INER INF1427/2025, belongs to clade 2.3.4.4b and, unlike the strain from the first case, has a highly pathogenic avian influenza signature in the HA segment. The HA segment is highly divergent from the LPAI A(H5N2) strains collected from the human case and birds in Mexico in 2024. The recent case clusters more closely with A(H5N1) viruses of clade 2.3.4.4b genotype B3.2.
