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Home › Topics › Infectious Diseases › Infections A-Z › Avian Influenza › General Information ›Frequently Asked Questions ›  Avian influenza viruses
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Avian influenza viruses

Apart from HPAI H5N1, have other avian influenza viruses ever infected humans?

Yes. Four other avian influenza subtypes have caused illness in humans, but the outbreaks were not as severe as those caused by the HPAI H5N1 strain.

Influenza A/H9N2 strain, which is not highly pathogenic in birds, caused mild cases of illness in two children in Hong Kong in 1999 and in one child in mid-December 2003, also in Hong Kong .

An outbreak of highly pathogenic H7N7 avian influenza in birds, which began in the Netherlands in February 2003, caused the death of one veterinarian (from an acute respiratory illness) two months later, and mild illness (mainly conjunctivitis and minor respiratory symptoms) in 88 poultry workers and members of their families. 

An outbreak of highly pathogenic H7N3 avian influenza also occurred in British Colombia, Canada in 2004 causing two cases of mild illness in humans. The outbreak of H7N3 in Norfolk in May 2006 caused one case of conjunctivitis.

On 05 May 2007, avian influenza A/H7N2 was identified in Wales and North West England, associated a market in Cheshire.  There were four cases of human disease associated with outbreak, three were hospitalised with flu-like symptoms.  Previously there had only been two separate reports of conjunctivitis in humans due to this virus

Are all of the currently reported outbreaks in birds equally dangerous for humans?

No. Based on the available data, outbreaks caused by HPAI H5N1 strain are presently of the greatest concern for human health.

In assessing risks to human health, it is important to know exactly which avian virus strains are causing the outbreaks in birds.

However, urgent control of all outbreaks of avian influenza in birds - even when caused by a strain of low pathogenicity - is of utmost importance. Research has shown that certain avian influenza virus strains, initially of low pathogenicity, can mutate (within 6 to 9 months) into a highly pathogenic strain if allowed to circulate in poultry populations.


Last reviewed: 13 August 2008