Avian tuberculosis (TB)

Occurrence: Worldwide.
Species affected: All.
Age affected: Older (over 2 years of age), rare in commercial flocks.
Causes: Bacterium- Mycobacterium avian.
Effects: Pale, regressed combs and wattles, depression, emaciation, anaemia, unthriftiness, icterus (yellow skin) and lameness. Public health significance.

Detailed causes:
Avian tuberculosis can be a serious chronic problem in older birds (over 2 years of age) of all species, but in rare in commercial flocks. It is caused by Mycobacterium avian, an acid-fast, bactillary, club-like bacterium. Curved and crooked forms of the bacterium can also occur.

It is spread by older carrier birds, or contaminated faecal material, soil, litter, aerosol, and cannibalism.

Special note
It has public health significance. Some cases of M. avium induced disease can occur in man. Immunosuppressed humans are very susceptible to this organism. It can spread to swine and cattle causing positive skin test. Backyard flocks, zoo and aviary birds over 2 years of age are commonly infected.

Clinical signs:
Pale, regressed combs, wattles, and depression can be seen. Emaciation, anaemia, unthriftiness, icterus (yellow skin) and lameness may occur.

Postmortem lesions
Internal yellow or grey-white pearl-shaped nodules in lungs, liver, spleen, intestines and bone marrow may be seen.

Gross lesions (nodules in lungs and bone) and TB skin test of wattles using antigen from state diagnostic laboratory are diagnostic. Acid-fast stain of Tubercle bacilli is also important. Histopathologic observations of tubercule and acid-fast bacilli can be done. Serology tests include ELISA and rapid agglutination test. It simulates lymphoid leucosis and coligranuloma.

Treatment and control:

Separate birds by age and remove skin-test-positive birds. Affected flocks should be quarantined.

Depopulation of commercial flocks is important. Exotic species can be given isoniazid (30 mg/Kg), ethambutol (30mg/Kg) and rifampicillin (45 mg/Kg) for 18 months.