H5亞型流感病毒之演化、全球疫情現況與防治策略

H5 Subtype Influenza Virus Evolution, Current Global Situation, and Prevention and Control Strategies

H5亞型高致病性禽流感（highly pathogenic avian influenza，HPAI）近年呈現全球化、跨物種、長期化的新面貌。其中，以2.3.4.4b分支為主的H5N1病毒自2020年後在野鳥族群中持續擴散，反覆造成家禽疫情與大規模撲殺，並逐步外溢至多種哺乳類，形成「泛動物流行」（panzootic）。哺乳類感染不僅反映生態衝擊與經濟風險，也使病毒獲得更多在哺乳類宿主內演化與適應的機會，進而提高人畜共通傳播與大流行風險。以往人類H5亞型流感感染多屬散發且與禽鳥暴露相關。但2024年美國乳牛群出現H5N1外溢且出現跨域傳播，並伴隨乳汁高病毒量、貓科動物重症與人類輕症病例，為風險評估的重要轉折。然而，病例偵測易受暴露史調查、採檢部位正確性與病毒排出動力學差異而有所限制。此外，伴侶動物如貓對H5N1具高度易感性，且與未殺菌乳品與生食寵物食品可能相關，突顯家庭端與產業端新增的暴露風險。本文以健康一體（One Health）觀點，綜合整理H5亞型流感病毒演化與擴散、禽鳥類與哺乳類流行態勢、乳牛事件與人類感染特徵，並討論監測、風險溝通、職業防護、疫苗與候選疫苗株整備等策略，以供感染控制、公共衛生與臨床應對參考。

H5 subtype highly pathogenic avian influenza (HPAI) viruses have shifted from episodic outbreaks to a sustained global threat. Clade 2.3.4.4b H5N1 now circulates widely in wild birds, repeatedly seeding poultry outbreaks and spilling over into an expanding range of mammalian hosts, consistent with a modern panzootic. Growing mammalian involvement increases opportunities for viral adaptation and reassortment, broadening zoonotic pathways and complicating pandemic risk assessment.
The detection of H5N1 in U.S. dairy cattle in 2024 was a key inflection point. There were reports of spread within and between farms, high viral burdens in milk, and secondary infections in cats and other mammals, followed by sporadic infections among exposed workers. Recent H5N1 human infections are frequently mild, including conjunctivitis, and detection is limited by incomplete exposure histories, variation in optimal sampling sites, and heterogeneous viral shedding. Companion animals, particularly cats, appear highly susceptible, and emerging reports implicate contaminated raw milk and possibly raw pet foods in severe feline illness, highlighting new household-level exposure pathways.
This review summarizes current evidence for H5 evolution and dispersal, avian and mammalian epidemiology, and the dairy cattle event as a turning point in risk evaluation. Clinical and surveillance implications for human infection are discussed, along with One Health preparedness priorities, including integrated surveillance across wildlife, poultry, and livestock; occupational protection for high-risk workers; risk communication on avoidable exposures, such as unpasteurized milk and raw animal products; and continued development of vaccines and candidate vaccine viruses for rapid response.