History of Major Epidemics of Avian Influenza in Humans and Public Health Perspectives

Avian influenza (AI) has had great impacts on global health and socioeconomics in the past two decades. Among many newly emerged influenza viruses, avian influenza viruses (AIVs) have played either indirect or direct role in human infections. The continuous evolvement of AIVs through antigenic drift and genetic reassortment has led to emerging diversities of local virus strains or variants. These dynamic changes of AIVs, even low pathogenic avian influenza (LPAI) viruses, have not only affected poultry health but also resulted in severe and fatal human cases. Moreover, the persistence of these viruses at a population level may lead to outbreaks of AI occurring year after year in a vicious cycle, if they are not completely eradicated. In light of the emergence of novel H7N9 and other subtypes of AIVs in China in recent years, residents of Taiwan who live closely to this neighboring country must be well prepared in case these viruses are imported. Furthermore, the potential for interspecies transmission to humans from either of the two subtypes of avian H5N2 and H6N1 viruses increases the risk assessment of potential public health threats coming from continuous viral mutations. These two AIV subtypes are relevant in chickens and have been endemic in Taiwan for many years, and the newly emerged novel three subtypes (H5N2, H5N3, and H5N8 clade 2.3.4.4) of AIVs that have spread island-wide since January of 2015 must be expeditiously assessed for public health risks. In summary, this article discusses the history, virology, and epidemiology of avian influenza in humans. We believe that fully understanding virological and epidemiological characteristics of avian influenza viruses and the history of past pandemics or major epidemics will help strengthen the effectiveness of prevention and control measures.