Avian influenza (AI) viruses, commonly known as bird flu, infect a wide range of hosts, including humans and swine. The natural reservoir lies in populations of wild aquatic birds such as ducks and shorebirds. AI viruses are members of the family Orthmyxoviridae, Type A which is subdivided into categories (strains) depending on the outer proteins H (Haemagglutinin) and N (Neuraminidase). These outer proteins can be combined to create different strains, for example H5N1, H9N2. Influenza viruses have a single stranded RNA genome that is spilt into eight different segments, which are surrounded by a capsid and an envelope.
- Avian influenza is a notifiable disease and should be reported.
Please see the Defra website for advice on how to spot and report the disease.
AI strains can be categorised into 2 types;
Highly pathogenic avian influenza (HPAI) is the more serious of the two, often being fatal in birds. Clinical signs include:
- Swollen head
- Blue discolouration of neck and throat
- Loss of appetite
- Respiratory distress such as gaping beak, coughing, sneezing, gurgling, rattling
- Fewer eggs laid
- Increased mortality
Low pathogenic avian influenza (LPAI) is less serious, with the severity depending on the species of bird and whether it has other infections. Clinical signs include mild breathing problems, but affected birds will not always display these signs (for example, ducks and geese can often be asymptomatic).
The disease spreads by direct contact or through contaminated faeces and bodily fluids. New AI virus strains are created frequently which means that there is a constant risk that one of the new strains may spread easily among people. There is some evidence for limited person-to-person spread of avian influenza and though there is no evidence for efficient and sustained transmission, there is a constant risk that one of the new strains may spread easily among people, which could result in a new influenza virus pandemic.
HPAI is spread across the globe, featuring mainly in North America, Asia, Europe and West Africa. LPAI is endemic in the Middle East and South East Asia, with poultry populations being infected with strains such as H9N2. Due to the different migratory patterns of each species, it is difficult to predict where each strain will spread.
Impact for Society – what are we doing?
Avian Influenza continues to be a threat to the worldwide poultry industry. The viruses responsible for all four of the worldwide human influenza pandemics seen in the last 100 years have originated from birds. An effective control strategy for avian influenza in domesticated poultry is therefore an essential element in the protection of both bird and human populations.
Many groups at the Institute work on and around AI. Together they are researching areas such as how LPAI can change into HPAI and how bird immune systems react to the virus. This work is able to inform better diagnostics, breeding and vaccination.
* Image by Frederick Murphy courtesy of Public Health Image Library (PHIL)