Tuberculosis

Description

Tuberculoisis is a general term for diseases caused by the tuberculous group of bacteria, Mycobacteria species. Mycobacterium tuberculosis, Mycobacterium bovis, Mycobacterium avium are host adapted to humans, cattle and birds respectively. All three types can produce disease in other species; Mycobacterium tiberculosis is the most host specific strain and rarely causes progresive disease in species other than humans, Mycobacterium bovis can affect a number of other species, see Bovine Tuberculosis. Mycobacterium avium is the only type that causes disease in birds but it can also affect mammalian species, see Avian Tuberculosis.

Infection is usually via inhalation of infective droplets, but can aslo be by ingestion of contaminated feed or water, and occasionally via coitus or milk. The primary focus of infection is determined by the route of infection. Characteristic granulomatous tubercles develop. These become nectrotic, shedding the infective organism which disseminates to other body systems initiating secondary foci.

Diagnosis

Clinical Signs

Intradermal Tuberculin test.

Pathology

Grossly:

• Spherical nodules
• Caseous content
• Fibrous capsule usually

Histologically:

• Granuloma
• Central necrosis
• Epitheliod and giant cells at periphery

Treatment

Control measures depend on the species affected and the prevalence of the disease. The BCG vaccine provides protection for humans, if disease occurs treatment is with antibiotics. Chemotherapy has also been attempted in elephants and primates.

The test and slaughter policy is the only method of eradicating TB, positive reactors are culled and testing of the herd is undertaken every 3-6 months.

References

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
• Radostits, O.M, Arundel, J.H, and Gay, C.C. (2000) Veterinary Medicine: a textbook of the diseases of cattle, sheep, pigs, goats and horses Elsevier Health Sciences