AVIAN INFLUENZA ("BIRD 'FLU")

GENERAL FACTS

BACKGROUND INFORMATION

Avian influenza (AI), commonly referred to as "bird 'flu", was first recognized in the United States in 1924-25, and is a highly contagious viral disease which can affect many avian species. Although Falconiformes are not particularly susceptible to the disease, it can affect them and, of course, any bird can act as a vector (spreading agent) of the disease.

AI affects the birds' respiratory, digestive and/or nervous system, and is caused by a "Type A" influenza ('flu) virus. Currently, there are two types of avian influenza virus recognised by science - low pathogenicity (LPAI) and high pathogenicity (HPAI) influenza.

In Italy , around 1878, "fowl plague" - a highly pathogenic form of avian influenza - struck, and the disease struck again in 1929; both times it was eradicated. Highly pathogenic avian influenza A (HPAI) viruses of the H5 and H7 HA subtypes have occasionally been isolated from free-living birds in Europe and elsewhere, and non-pathogenic and mildly pathogenic influenza A viruses regularly occur world-wide. In Great Britain , the last outbreak of avian influenza was in 1991.

Outbreaks due to HPAI have been recorded in Pennsylvania , USA , in 1983 and 1984. Outbreaks have also occurred in Australia , Chile , Hong Kong , Italy , Mexico and Pakistan . A serious outbreak of avian influenza occurred in the Netherlands in 2003, and spread to Belgium and Germany . The outbreak affected over 250 farms and resulted in the slaughter of over 28 million poultry. Japan , South Korea and South-East Asia were the scenes of another outbreak early in 2004, and this outbreak is still ongoing in China and parts of South-East Asia ; there is evidence that H5 viruses of low pathogenicity may mutate and become highly pathogenic.

Early in 2004, there was also a small number of avian influenza cases in North America ( USA and Canada ). The strain affecting birds in Texas was typed as H5N2, a different strain from that occurring in South-East Asia . More recent reports of infection have concerned birds in Africa, Asia and Europe, most recently in France .

Clinical signs of avian influenza include birds showing oedema (s welling due to the retention of fluids in the tissues) of the head, cyanosis (a blueing) of the comb and wattles, lack of appetite, respiratory distress, diarrhoea and a drop in egg production. Affected birds may die without any apparent signs of disease. There is considerable variation in the clinical picture and the severity of the disease.

Transmission of AI is through direct contact with secretions from infected birds, especially faeces, contaminated feed, water, equipment and clothing. Apparently "normal" (i.e. seemingly unaffected) waterfowl and sea birds may introduce the virus into populations of birds, and cracked or broken contaminated eggs can infect chicks in the incubator.

On 30 April 2003 , The Diseases of Poultry (England) Order 2003 came into force, and this legislation introduced Community measures for the control of AI; similar legislation covers Scotland and Wales .

In the event of an outbreak of AI, main aspects of disease control will include a prohibition on the movements of animals, litter and vehicles into and out of any infected location(s). All affected premises and vehicles will have to be cleansed and disinfected to standards laid down by Defra (Department for Environment, Food and Rural Affairs), and Schedule 3 of the Animal Health Act 1981 provides for the compulsory slaughter of diseased birds and also any birds suspected of being infected or which have been exposed to the infection. In addition, all eggs on affected premises must be destroyed.

In such cases, Defra will also impose movement restrictions on all birds and hatching eggs within a 3 km radius, and a 10 km radius "observation zone". All birds will have to be confined to their living quarters, and all markets, fairs, shows and field meets are likely to be prohibited. All used litter/substrate and faecal material from affected premises will have to be properly removed by authorised removal companies, and disposed of in line with legal requirements.