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During October 2022-March 2023, highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b virus caused outbreaks in South Korea, including 174 cases in wild birds. To understand the origin and role of wild birds in the evolution and spread of HPAI viruses, we sequenced 113 HPAI isolates from wild birds and performed phylogenetic analysis. We identified 16 different genotypes, indicating extensive genetic reassortment with viruses in wild birds. Phylodynamic analysis showed that the viruses were most likely introduced to the southern Gyeonggi-do/northern Chungcheongnam-do area through whooper swans (Cygnus cygnus) and spread southward. Cross-species transmission occurred between various wild bird species, including waterfowl and raptors, resulting in the persistence of HPAI in wild bird populations and further geographic spread as these birds migrated throughout South Korea. Enhanced genomic surveillance was an integral part of the HPAI outbreak response, aiding in timely understanding of the origin, evolution, and spread of the virus.

We analyzed 15 cases of highly pathogenic avian influenza (HPAI) clade 2.3.4.4b virus infections detected in wild birds in South Korea during September 2023-March 2024. We isolated and sequenced 8 H5N1 and 7 H5N6 viruses. We investigated spatiotemporal transmission dynamics by using a Bayesian discrete trait phylodynamic model that incorporated geographic and host species information. Our source-sink dynamics support introductions of H5N1 viruses from northern Japan to South Korea and subsequent spread through multiple regions in South Korea. The H5N6 viruses were most likely introduced into southwestern South Korea and spread northeastward. Wild waterfowl, especially wild ducks, played a key role in transmission of both H5N1 and H5N6 viruses. Our data showed multiple introductions and extensive spread of HPAI clade 2.3.4.4b viruses and bidirectional transmission between Japan and South Korea. Our results highlight the value of enhanced active surveillance for monitoring HPAI viruses, which can provide insight into preventing future outbreaks.

We isolated novel reassortant avian influenza A(H5N6) viruses containing genes from clade 2.3.4.4b H5N1 virus and low pathogenicity avian influenza viruses in carcasses of whooper swans and bean geese in South Korea during December 2023. Neuraminidase gene was from a clade 2.3.4.4b H5N6 virus infecting poultry and humans in China.

We investigated the antimicrobial resistance (AMR) rates and profiles of Staphylococcus spp. and Escherichia coli ( E.coli ) isolated from dogs and cats in Seoul, South Korea during 2021–2023. We analyzed AMR profiles of Staphylococcus spp. and E. coli isolated from 2,180 samples (1,859 canine and 321 feline) collected from 36 veterinary clinics in Seoul, South Korea, as part of the Korean Veterinary Antimicrobial Resistance Monitoring System (2021–2023). A total of 484 Staphylococcus spp. isolates and 158 E. coli isolates were identified and used for AMR test. Staphylococcus spp. isolates exhibited the highest resistance to penicillin in both dogs (85%) and cats (29.81%). Multidrug-resistant (MDR) Staphylococcus spp. was more prevalent in dogs (65%) than in cats (14.42%), with three S. pseudintermedius isolates from dogs and a S. pseudintermedius isolate from a cat showing resistance to eight antibiotic classes. Methicillin-resistant S. pseudintermedius (MRSP) constituted 105 out of 284 S. pseudintermedius isolates (36.97%) in dogs and seven strains out of 14 (50%) in cats. E. coli isolates demonstrated the highest resistance to cefalexin in both dogs (61.72%) and cats (56.67%). The prevalence of MDR E. coli was higher in dogs (37.5%) than in cats (26.67%). This study highlights the concerning prevalence of AMR in commensal or potentially opportunistic pathogens from companion animals, particularly in dogs. It is crucial to promote the prudent use of antimicrobials in companion animals and ensure the ongoing monitoring of trends in antimicrobial-resistant bacteria to mitigate the selection and spread of antibiotic-resistant bacteria between humans and companion animals.