Fowl cholera infection can range from acute systemic and rapidly fatal to chronic and localised infections.  The morbidity and mortality may range from low to high.

The clinical signs vary depending on the Pasteurella multocida strain and the susceptibility of the flock.  In acute fowl cholera, death is often the first indication of disease.  In acute fowl cholera there are vascular disturbances that may result in fever, loss of appetite, ruffled feathers, diarrhoea from the nose, eyes and mouth and an increased respiratory rate.  Cyanosis (bluish discolouration) of the comb and wattles often occurs shortly prior to death. In chronic fowl cholera the signs are associated with local infections, e.g. swollen wattles, sinuses and joints as well as infection of the respiratory tract and middle ear resulting in pneumonia and torticollis (twisted neck).

Infection occurs following direct contact with susceptible birds from clinically affected or carrier birds. Indirect infection may occur through contact with rodents, wild birds and contaminated people and equipment, particularly feeders and drinkers.