Avian influenza viruses can be classified according to their ability to cause severe disease (pathogenicity) as either highly pathogenic or low pathogenic. The viruses are described by their major antigen determinants, H (for haemagglutinin) and N (neuraminidase). The current strain of concern is a highly pathogenic H5N1.
In birds we are mainly concerned with H5 and H7 subtypes. It is known that the LPAI H5 and H7 virus subtypes can mutate into the highly pathogenic form that causes serious illness and deaths in birds, although in water fowl the disease may not be apparent.
Low pathogenic avian influenza
Typically, infection with LPAI is often difficult to detect, with very few if any clinical signs. An infected flock might show signs of respiratory distress, diarrhoea, a loss of appetite or a drop in egg production of more than 5%. If you are suspicious your flock has any form of avian influenza you must contact your local animal health office immediately.
Highly pathogenic avian influenza
Typically this form of the disease presents suddenly, often with very high mortality, with affected birds developing swollen heads, a blue colouration of the comb and wattles, dullness, lack of appetite, respiratory distress, diarrhoea and significant drop in egg production. However, there can be considerable variation in the clinical picture and severity of the disease. If you are suspicious your flock has any form of avian influenza you must contact your local animal health office immediately.
If you suspect signs of any notifiable diseases, you must immediately notify your Scotland: field service local office at the Animal and Plant Health Agency (APHA). Failure to do so is an offence. Sign up to the APHA Alerts Service to keep up to date with the latest news.
Human health implications
Some strains of bird flu can pass to humans but this is very rare. It usually requires very close contact between humans and infected birds. Find out more at: bird flu and human health.
Animal Health and Welfare
Agriculture and Rural Economy Directorate