Reported Human Infections with Avian Influenza A Viruses

Human infections with avian influenza A viruses are uncommon but have occurred sporadically in many countries, usually after unprotected exposures (e.g. not using respiratory or eye protection) to infected poultry or virus-contaminated environments and have resulted in mild-to-severe illness with a wide range of symptoms and complications. A small number of human infections with avian influenza A viruses have been attributed to exposure to infected wild birds. For some human infections, the source of the virus infection was not determined. Human infections have occurred with different subtypes of low pathogenic and highly pathogenic avian influenza A viruses. The designation of “low” versus “highly” pathogenic avian influenza A virus refers to specific criteria, including mortality in experimentally infected poultry, and not to the severity of illness with human infections. Clinical illness associated with human infections with avian influenza A viruses does not necessarily correlate with virus pathogenicity in infected birds.

Low Pathogenic Avian Influenza A Virus Infections*

Subtypes of low pathogenic avian influenza (LPAI) A viruses that have been virologically confirmed to have infected people include A(H6), A(H7), A(H9), and A(H10) viruses.

Highly Pathogenic Avian Influenza A Virus Infections*

Subtypes of highly pathogenic avian influenza (HPAI) A viruses that have been virologically confirmed to have infected people include A(H5) and A(H7) viruses.

Human-to-Human Transmission of Avian Influenza A Viruses

Human-to-human transmission of avian influenza A viruses is rare. Probable limited, non-sustained, human-to-human transmission has been reported in a small number of people without poultry exposures who had close unprotected exposure to a symptomatic index case of HPAI A(H5N1) virus infection, HPAI A(H7N7) virus infection, or LPAI A(H7N9) virus infection. Most reported cases of probable limited, non-sustained, human-to-human transmission have occurred among blood-related family members after unprotected, prolonged close household exposure to a symptomatic family member. However, a small number of reported cases occurred after unprotected, prolonged close exposure to a very sick family member in a hospital. A few cases of probable limited, non-sustained, human-to-human transmission in a hospital have been reported among unrelated patients after unprotected exposures.

*Sources: Adapted from Uyeki T and Peiris M. Infectious Disease Clinics of North America 2019; and World Health Organization reports. For the latest summary, case counts of human infections, and risk assessment, see the World Health Organization Influenza at the human-animal interface summary and assessment:  https://www.who.int/teams/global-influenza-programme/avian-influenza/monthly-risk-assessment-summaryexternal icon