Highly Pathogenic Avian Influenza A(H5N1) Virus Infection in Cats, South Korea, 2023

Abstract

In July 2023, cases of highly pathogenic avian influenza (HPAI) were reported at 2 shelters for stray cats in Seoul, South Korea. The cause of infection was suspected to be improperly sterilized raw food made from domestic duck meat, which was manufactured in South Korea. All viruses isolated from cats at the shelters and from the raw food belonged to HPAI A(H5N1) clade 2.3.4.4b. The gene constellation of all viruses was most similar to that of viruses isolated in Korea in November 2022. Of note, the viruses isolated from infected cats harbored mutations E627K or D701N in polymerase basic 2, which are indicative of adaptation to mammals. Postmortem examination revealed systemic pathologic lesions and the presence of widespread virus in different tissues. Thus, consumption of raw duck meat contaminated with HPAI virus likely caused systemic symptoms and death in cats, indicating the introduction of mammal-adapted mutations of the virus.

Keywords: H5N1; South Korea; cat; highly pathogenic avian influenza; influenza; raw duck meat; viruses; zoonoses.

Figure 1

Gross, microscopic, and immunohistochemistry (IHC) findings in cats infected with highly pathogenic avian influenza A(H5N1) virus, South Korea, 2023. Findings are shown for cat carcasses from shelter 1 (Y cat carcass no. 3) and shelter 2 (G cat carcass no. 1). A–D) Gross findings: A) severe congestion and edema in the lungs; B) congestion and edema in the lungs; C) lack of lesions in the small intestine; D) bloody diarrhea in the small intestine (D). E–J) Hemotoxylin and eosin staining: E) brain showing no lesions; F) multifocal gliosis in the brain; G) interstitial pneumonia with focally extensive vascular thrombosis; H) interstitial pneumonia characterized by invasion of the alveolar lumina by mixed neutrophils and macrophages; I) intestine showing no lesions; J) necrotic enteritis with denuded villi. K–P) Immunohistochemical staining: K) brain showing no influenza virus antigens; L) influenza virus antigens in the neurons; M) influenza virus antigens in alveolar macrophages and bronchial epithelial cells; N) influenza virus antigens in alveolar macrophages and bronchial epithelial cells; O) influenza virus antigens in the small intestine; P) influenza virus antigens in the crypt epithelium and blood vessels in the submucosa. Original magnification ×100, except panel F, in which original magnification was ×10.

Figure 2

Maximum-likelihood phylogenetic tree for the hemagglutinin (HA) gene in study of highly pathogenic avian influenza virus A(H5N1) infection in cats, South Korea, 2023. The phylogenetic tree is based on H5N1 HA sequences of viruses isolated recently, as well as on the HA gene sequence of other H5Nx viruses. Bootstrap values (1,000 replicates) >70% are displayed at the branch nodes. The black circle denotes virus isolated from poultry in South Korea, 2022–2023, and the black triangle denotes viruses isolated from raw duck meat used for cat food. The blue shaded square denotes viruses isolated from cats in shelter 1, and the red square indicates viruses isolated from cats in shelter 2. The blue outlined square indicates viruses isolated from cats in shelter 1 by SNU. Scale bar indicates number of nucleotide substitutions per site. SNU, Seoul National University.

Figure 3

Maximum-likelihood phylogenetic tree for the neuraminidase (NA) gene in study of highly pathogenic avian influenza virus A(H5N1) infection in cats, South Korea, 2023. The phylogenetic tree is based on sequences of H5N1 NA sequences of viruses isolated recently, as well as on the HA gene sequence of other H5Nx viruses. Bootstrap values (1,000 replicates) >70% are displayed at the branch nodes. The black circle denotes virus isolated from poultry in South Korea, 2022–2023, and the black triangle denotes viruses isolated from raw duck meat used for cat food. The blue shaded square denotes viruses isolated from cats in shelter 1, and the red square indicates viruses isolated from cats in shelter 2. The blue outlined square indicates viruses isolated from cats in shelter 1 by SNU. Scale bar indicates number of nucleotide substitutions per site. SNU, Seoul National University.