Avian influenza, or bird flu, is an illness caused by influenza A viruses. While most forms of bird flu are mild, concern has grown over more serious forms of bird flu, particularly the H5N1 virus that has been known to cause death in humans. Many wild birds carry influenza viruses with no symptoms, but when flu viruses spread to domesticated birds, they may become ill. Because of the deadly H5N1 outbreaks that have been seen in places like Asia and Europe since 2003, and the rare instances of human infection, The U.S. Centers for Disease Control urges all poultry workers to know the signs of illness in birds and take preventive measures.
Respiratory and Intestinal Symptoms
Chickens with bird flu may cough, sneeze and have nasal discharge, which may be bloody. Respiratory symptoms may be mild in birds suffering from common, mild forms of avian influenza, according to the World Health Organization. Chickens sick with bird flu may also have diarrhoea.
Chickens infected with bird flu may have decreased egg production, and may lay soft-shelled or misshapen eggs, according to the Occupational Safety and Health Administration (OSHA).
Changes in Appearance
Chickens with avian influenza may exhibit purple discolouration of the wattles (fleshy growths that hang from the throat), combs (growth on top of the head) or legs, according to the U.S. Centers for Disease Control and Prevention. The head, eyelids, comb, wattles and hocks may also begin to swell. Pinpoint haemorrhages can appear, especially on the feet and shanks.
Lack of energy is a common symptom of bird flu, as well as loss of appetite and decreased coordination. Some birds with a mild strain of avian influenza may simply have ruffled feathers.
Highly lethal forms of avian influenza can cause sudden death in poultry. Chickens, especially young birds, may succumb to the illness so quickly that no symptoms are obvious before death, according to the University of Florida. According to WHO, the lethal H5N1 strain of avian influenza has a mortality rate that can reach 100 per cent within 48 hours.