Detection of Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Genotype D1.2 Virus in Swine after Experimental Inoculation.

Highly pathogenic avian influenza H5NX clade 2.3.4.4b viruses continue to circulate globally. Reintroduction of Eurasian lineage viruses into North America and reassortment with endemic low pathogenicity strains have resulted in new genotypes, including D1.2. To assess pathogenicity and cellular tropism, we intranasally inoculated genotype D1.2 virus into pigs. We isolated virus from nasal secretions from most inoculated animals for multiple days. At 5 days postinoculation, PCR and immunohistochemistry detected virus in musculoskeletal, respiratory, digestive, lymphatic, and nervous systems, and virus was isolated from meat juice. At 35 days postinoculation, we detected viral antigen and low levels of RNA in the brain of an animal with lesions consistent with a viral etiology and found viral antigen in the ethmoid of 2 animals. Consistent detection in nasal swab specimens, combined with subclinical respiratory infection, suggest that identifying infection in commercial swine without overt respiratory signs could be difficult.