Influenza virus: Highly pathogenic avian influenza. In BSL3 and BSL4 agents: Epidemiology, microbiology, and practical guidelines. (Book Chapter)

Influenza A viruses are known since decades to cause disease in avian and mammalian species. The natural reservoirs are wild birds, which host all subtypes. Stable lineages are also established in domestic poultry, humans, pigs or horses. In humans, new strains with an avian genetic background were successively introduced in 1918 (H1N1), 1957 (H2N2) and 1968 (H3N2), leading to 3 pandemics separated by years of seasonal activity. Each subtype superseded the previous strain, but in 1977 the H1N1 virus was reintroduced in the human population and both H3N2 and H1N1 viruses co-circulate since. Despite effective vaccines, about 250 000 to 500 000 people die each year of seasonal influenza. In domestic poultry, certain subtypes become highly pathogenic and can be lethal for humans, but so far no highly pathogenic avian influenza (HPAI) virus acquired the ability of sustained human-to-human transmission. For instance during the 2003 outbreak of HPAI H7N7 viruses in the Netherlands, 30 million birds were killed or culled. Several infected individuals developed a mild disease but one veterinarian died. While this virus has successfully been controlled, the HPAI H5N1 virus which emerged in Asia spread worldwide, infecting more than 400 people with a 60% mortality rate. This chapter will focus on HPAI viruses, in particular H5N1, as it was, until recently, expected to cause the next pandemic.