Inhalation of large amounts of the infectious form of the mold or reduced resistance of the bird apparently results in infection. In adult turkeys, the disease more often affects the male. In the acute form in young birds, main symptoms are gasping, sleepiness, loss of appetite and sometimes convulsions and death. Occasionally the organism invades the brain, causing paralysis or other forms of nervous symptoms. The more chronic form in older birds usually results in loss of appetite, gasping or coughing and a rapid loss of body weight.
Mortality is usually low and only a few birds are affected at one time.
The disease produces hard nodular areas in the lungs and an infection of the air sacs. In some birds, colonies of mold growth can be seen on the air sac membranes. Diagnosis is usually made from history, symptoms and lesions. It may be necessary to base diagnosis on microscopic lesions. The disease can usually be prevented by avoiding moldy litter, feed or premises.