Salpingitis and multiorgan lesions caused by highly pathogenic avian influenza A(H5N1) virus in a cat associated with consumption of recalled raw milk in California

A panzootic caused by highly pathogenic avian influenza (HPAI) A(H5N1) virus, clade 2.3.4.4b, has affected many animal species around the world since 2021. In March 2024, genotype B3.13 of this virus was identified in dairy cattle in the United States, following a spillover event from wild birds. Mammary gland lesions were a key finding in infected cows, with infectious virus detected in their milk. Raw milk is sold legally in retail establishments in multiple US states, including California. In November 2024, HPAI A(H5N1) virus, clade 2.3.4.4b, genotype B3.13, was detected in raw milk sold commercially in California and then in bulk milk tanks. The affected product later was recalled. We describe an 8-mo-old cat with a history of severe illness after consuming this raw milk before it was recalled. The cat was euthanized and submitted for postmortem examination and diagnostic workup. Autopsy and histopathology revealed icterus, nasal discharge, hydrothorax, gliosis, and necrotizing pneumonia, hepatitis, and salpingitis, among other lesions. Immunohistochemistry for influenza A virus revealed intralesional immunolabeling in many organs. Molecular detection was positive for HPAI A(H5N1) virus, clade 2.3.4.4b, genotype B3.13. To our knowledge, HPAI A(H5N1) virus has not been reported previously in cats after consuming raw milk purchased from a retail establishment, nor has salpingitis been associated with HPAI A(H5N1) virus infection in a mammal. Hepatic damage and icterus were prominent findings in our case rather than primary involvement of the CNS.