Symptoms of avian influenza infection

How long does it take for humans to develop symptoms after infection?

The typical time from exposure to the source of infection to onset of influenza is likely to be between three and five days, with a maximum time of up to ten days.

How severe is the human illness caused by avian influenza?

This appears to vary. In the Hong Kong outbreak of avian influenza (subtype HPAI H5N1) infection in 1997 there were 18 human cases and six deaths. In the Netherlands outbreak caused by H7N7 avian influenza there were 89 cases with minor symptoms like conjunctivitis (eye infection) including one death.

In the current outbreak that originated in Asia (caused by HPAI H5N1) human illness is very severe in most reported cases. Some cases have been reported to have fully recovered; other cases have reportedly died with pneumonia. Factors underlying severity of illness are not well understood.

Have there been any human cases of avian influenza in the UK ?

In the 2007 H7N2 outbreak in Wales and North West England, there were four human cases, three of which were hospitalised with flu-like symptoms.  In the 2006 H7N3 poultry outbreak in Norfolk, there was one associated human case who suffered from conjunctivitis. Previous to this, in England in 1996 there was a single case of a female farmer who acquired H7 influenza and suffered conjunctivitis after cleaning out a poultry house. There have been no human cases imported into England associated with the recent poultry outbreaks in southeast and east Asia. People with recent infections acquired in southeast and East Asia are unlikely to present in the UK because infection is rare and the time from exposure to infection and onset of symptoms is short. There were no known human cases in the UK associated with the H5N1 avian influenza identified in a swan in Scotland in 2006 or with the outbreak in Suffolk in early 2007.

If I have avian influenza what symptoms can be expected?

Early symptoms in humans are likely to be similar to normal influenza such as fever and cough. Some avian influenza viruses do not cause flu-like symptoms but instead will cause itchy, sore red eyes (conjunctivitis).

What are the symptoms of avian influenza in humans?

The symptoms of AI in humans vary considerably depending on the subtype of the influenza virus involved.

• HPAI H5N1 infection causes a severe respiratory infection in most people
• H7N7 infection causes conjunctivitis and a mild respiratory infection although in some cases the respiratory infection can become severe
• H9N2 infection causes a mild respiratory infection
• H7N3 infection causes predominantly conjunctivitis in humans

Last reviewed: 13 August 2008