It is caused by an acid-fast bacterial rod known as mycobacterium. In humans, TB is caused by M. tuberculosis, M. bovis, and occasionally, M. avium. In birds, M. avium is the usual agent although M. bovis and M. tuberculosis can cause disease as well. In humans, the incidence of TB is increasing, especially in people whose immune systems are compromised, such as those infected with the AIDS virus.
All birds are susceptible to avian tuberculosis.
It is most prevalent where there is a high population density, such as in zoos, or collections of birds. Brotogerid parakeets, ringneck and related parakeets, amazons, Grey Cheeks, and pionus parrots seem to be especially susceptible. Although sudden death can occur in a bird with normal body weight, the usual presentation of a bird with TB is one of progressive weight loss in spite of a good appetite. Depression, diarrhea, increased thirst, and respiratory difficulty may also be present. Decreased egg production often occurs in birds that were laying eggs.