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

Pathology

• Grossly:
  • Yellowish spherical nodules
  • Caseous content
  • Fibrous capsule usually
• Histologically:
  • Granuloma
  • Central necrosis
  • Epitheliod and giant cells at periphery