Causative agent 
- Mycobacterium bovis


Differential diagnosis 
- Actinobacillosis
- Actinomyces pyogenes infection


1. History taking 
- History of cattle introduced from TB endemic
  area or infected herds


2. Clinical examination 
- No clinical signs in early stage of infections
- Gradual emaciation, enlargement of lymph
  nodes and cough in advanced cases
- Clinical evidence of tuberculosis is rare


3. ELISA 
- No diagnostic value in early infection because of
  lower antibody level to M. bovis and sensitization
  by environmental mycobacteria
- Useful to detect advanced infection or anergic
  animals
- Helpful as a complementary test


4. Gamma-interferon assay (IFN-γ) 
- Whole blood is cultured with avian, bovine PPD or
  PBS (nil antigen) and incubated for 16 hr at 37°C
- Lymphocytes of infected cattle should be stimulated
  and secrete IFN-γ
- Plasma sample collection
- Using commercial EIA kit (CSL, Australia)
- Detection of reactors by a comparative method


5. Tuberculin test 
- Primary test for diagnosis of TB in the live animal
- Single intradermal test
- Tuberculin PPD (1 mg/ml) 0.1 ml is injected into a
  site of the caudal fold or the mid-neck
- The site is first clipped and examined to be free from
  evident lesions
- The skin fold is measured with callipers twice (before
  and 72 hr after injection)
- A positive result is judged by an increase in the skin
  fold thickness of at least 5 mm
- In suspecious cases, the test should be repeated
  one more time after 60 days