Can Humans Contract Avian Influenza?
Avian Influenza in Humans
There are many different subtypes of type A influenza viruses. These subtypes differ because of changes in certain proteins on the surface of the influenza A virus, which includes hemagglutinin (HA) and neuraminidase (NA) proteins.
There are 16 known HA subtypes and 9 known NA subtypes of influenza A viruses. Many different combinations of HA and NA proteins are possible. Each combination represents a different subtype, and all known subtypes of influenza A viruses can be found in birds.
Usually, the term "avian influenza virus" refers to influenza A viruses found chiefly in birds, but infections with these viruses can occur in humans. The risk from the disease is generally low in most people, because the viruses do not usually infect humans. However, confirmed cases of human infection from several subtypes of avian influenza infection have been reported since 1997.
Most cases of infection in humans have resulted from contact with infected poultry (domesticated chicken, ducks, and turkeys) or with surfaces contaminated with secretions/excretions from infected birds. The spread of the avian influenza virus from one ill person to another has been reported only rarely, and transmission has not been observed to continue beyond one person.
During an outbreak of avian influenza among poultry, there is a possible risk to people who have contact with infected birds or with surfaces that have been contaminated with secretions or excretions from infected birds. Avian influenza H5N1 in humans is currently limited and not a pandemic flu.
Human H5N1 influenza infection was first recognized in 1997, when this virus infected 18 people in Hong Kong, causing six deaths. Since 2003, more than 100 human H5N1 flu cases have been diagnosed in Thailand, Vietnam, Cambodia, Indonesia, and China. Of those cases, more than half have died as a result of avian influenza.
(Click Pandemic Flu for more information about flu pandemics.)