The prevalence of highly pathogenic avian influenza (HPAI) A(H5N1) viruses has increased in wild birds and poultry worldwide, and concomitant outbreaks in mammals have occurred. During 2023, outbreaks of HPAI H5N1 virus infections were reported in cats in South Korea. The H5N1 clade 2.3.4.4b viruses isolated from 2 cats harbored mutations in the polymerase basic protein 2 gene encoding single amino acid substitutions E627K or D701N, which are associated with virus adaptation in mammals. Hence, we analyzed the pathogenicity and transmission of the cat-derived H5N1 viruses in other mammals. Both isolates caused fatal infections in mice and ferrets. We observed contact infections between ferrets, confirming the viruses had high pathogenicity and transmission in mammals. Most HPAI H5N1 virus infections in humans have occurred through direct contact with poultry or a contaminated environment. Therefore, One Health surveillance of mammals, wild birds, and poultry is needed to prevent potential zoonotic threats.

高致病性禽流感 (HPAI) A(H5N1) 病毒在全球野生鸟类和家禽中的流行有所增加，并同时在哺乳动物中爆发。 2023 年，韩国报告了猫中爆发 HPAI H5N1 病毒感染。从 2 只猫中分离出的 H5N1 分支 2.3.4.4b 病毒在编码单氨基酸取代 E627K 或 D701N 的聚合酶碱性蛋白 2 基因中存在突变，这些突变与哺乳动物中的病毒适应有关。因此，我们分析了猫源性 H5N1 病毒在其他哺乳动物中的致病性和传播情况。这两种分离株均引起小鼠和雪貂的致命感染。我们观察到雪貂之间的接触感染，证实该病毒具有高致病性并在哺乳动物中传播。大多数人类 HPAI H5N1 病毒感染是通过直接接触家禽或受污染的环境发生的。因此，需要对哺乳动物、野生鸟类和家禽进行“One Health”监测，以防止潜在的人畜共患病威胁。