Avian influenza, also known as ‘Bird flu’, is a notifiable disease and must be reported immediately. It is caused by Orthomyxovirus Type A. There are high and low pathogenic strains that affect a wide range of avian hosts, and a natural reservoir lies in populations of wildfowl such as migratory ducks and geese. Currently, the risk of exposure in the UK is low, but increased outbreaks are common in the autumn due to the migratory pattern of waterfowl and environmental conditions becoming more favorable for virus survival. The virus has been found across East Anglia, Kent and the Midlands in the UK. North and Eastern Europe have a high incidence of highly pathogenic avian influenza (HPAI) outbreaks. The risk is greater when birds are in close proximity to migratory bird refuge areas such as tidal marshes and standing water.

The risk is continually reviewed. For further information and to find out the latest bird flu situation in England visit the Government website and Countryside Alliance.

Image credit: https://www.vetlexicon.com/avis/respiratory/images/avian-influenza-comb-wattle-edema/

Clinical signs

Highly pathogenic avian influenza (HPAI) causes mass, sudden mortality with cranial swelling and purple discoloration (cyanosis). Morbid birds may cough or sneeze and show neurological deficits with ataxia. Low pathogenic avian influenza (LPAI) can often be subclinical, especially in mixed back yard flocks. However, it will cause significant egg production drops in commercial breeders or layers with increased seconds and egg abnormalities (thinned shelled egg). Sudden feed and water consumption drops along with conjunctivitis, dyspnea, sinusitis and/or diarrhea. Any age can be affected and there are no breed predispositions, but it is over-represented in wild waterfowls.

Diagnosis

Diagnosis of avian influenza is based on clinical signs. In the UK, HPAI is a notifiable disease so DEFRA must be called. Government testing will include PCR. Cases of LPAI will require an oropharyngeal PCR swab, viral isolation from tissue samples and subtyping. 

Gross autopsy findings include significant hemorrhaging of the proventriculus and/or gizzard mucosa. Petechiations throughout the lymphoid tissue of the gastrointestinal tract also occur as well as cyanosis and necrosis of the comb and wattle. Petechial hemorrhages will be seen in epicardial fat, as well as pulmonary hemorrhage and edema. Mucosal plugs in the trachea and sinus from inflammation can be visualized, and necrotic foci in pancreas, spleen, heart. Birds will be severely dehydrated with congestion of the skeletal muscles. Edema of the head and neck may also be observed.

Treatment

In the UK, the treatment is controlled by DEFRA/APHA. Strict biosecurity must be implemented immediately, as soon as suspicion has been raised. HPAI cases will be controlled via depopulation of the flock. Government restriction may be implemented in the case of a national HPAI outbreak. Broad spectrum antibiotics can be given to birds with LPAI to control secondary infections. Exclusions zones will be put in place.

Prognosis

The prognosis for chickens with avian influenza is grave.

References

• Avian influenza

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