Avian influenza, or bird flu, is a viral infection common among birds worldwide. Wild birds carry the virus but typically do not become sick from it, but domesticated birds, such as turkeys, ducks and chickens, do. Bird flu is difficult to diagnose without laboratory work, according to the University of Florida Extension Service, as the symptoms are similar to other common diseases of domestic fowl. Bird flu is spread through the secretions of infected birds. There is no cure for bird flu so prevention is the key to stopping its spread.
Visible Symptoms of Bird Flu
Bird flu virus mutates rapidly and may cause mild or severe symptoms, depending on the strain of virus and the species of bird. Sometimes the only symptom is sudden death. The Centre for Disease Control warn that virulent forms have killed 90 to 100 per cent of a flock in 48 hours. Chickens may exhibit other symptoms when infected with less virulent strains. The eggs may have softer shells, and egg production may drop. The bird stops eating, develops diarrhoea and may have bloody discharge from the nostrils. The head, eyelids, comb, wattles and hocks may swell, or the wattles and comb take on a purple tinge. There may be signs of respiratory distress. The chicken may seem listless, have difficulty walking and have ruffled feathers. The feet and shanks may appear bruised. Poultry farmers should report these symptoms to state poultry regulators.
After death, chickens can be examined for more specific symptoms of avian flu. These symptoms include swollen blood vessels and signs of bruising or hemorrhaging in the trachea. Hemorrhaging in the proventriculus, the organ leading to the gizzard, and the gizzard itself are also postmortem symptoms. The gizzard lining may be loose and peels away easily. Forensic examination may reveal swelling and bruising near the breastbone and the heart and blood in the abdominal fat. Beneath the lower layer of skin, a yellowish fluid may be found. In broilers (young chickens raised for meat), the carcase may show severe dehydration.
A diagnosis of avian influenza can only be confirmed by a sample from the infected bird or flock, then isolating the virus and identifying it. Viral strains are distinguished by hemagglutinin (H) and Neuraminidase (N) antigens and given designations such as H5N2. Any diagnosis of bird flu in the United Kingdom must be reported to the Department for Environment Food & Rural Affairs (Defra). The site link is in the resources and the department can be contacted on 03459 33 55 77.