Diagnosis, control and prevention

 

DIAGNOSIS, CONTROL AND PREVENTION

Specimens to be collected

  • Specimens from live animals include aspirates from cavities, lymph nodes, biopsies, tracheobronchial lavages and centrifuged deposit from about 50 ml of milk in the case of suspected tuberculous mastitis. With dead animals, collect fresh and fixed (10% formalin) samples of lesions.

Diagnosis

  • Based on history, signs and post mortem lesions
  • Direct microscopy
    • The Ziehl-Neelsen (acid-fast) stain is used to stain smears from lesions and other specimens.
    • Organisms are appearing as slender, often beaded, red staining rods against a blue background.
    • Smears stained by fluorescent dyes (auramine, acridine orange or fluorochrome) allow the mycobacteria to be seen more easily if relatively small numbers are present.
  • Isolation
    • Several preliminary procedures are necessary in order to recover the comparatively slow growing mycobacteria
    • Selective decontamination to reduce significantly the number of fast growing contaminating bacteria.
    • Digestion or liquefaction of mucus is necessary. Mucin-trapped mycobacteria in specimens, such as broncho-tracheal exudates, may not be available for growth in cultures.
    • If mycobacteria are present, they must be concentrated by centrifugation.
    • For decontamination, the ground-up specimens must be treated with decontaminating agents, such as 5% oxalic acid, 4% sodium hydroxide followed by neutralization of the acid or alkali or 20% antiformin can be used and subsequently cultured in stone brink or Lowenstein Jensen media.
  • By animal inoculation
Inoculated suspected material
Mycobacterium tuberculosis
Mycobacterium bovis
Mycobacterium avium
Rabbits (I/V)
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Guinea pig (S/C)
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Chicken (I/V)
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  • Bacteriophage typing: A, B, C, I
  • Tuberculin test (Intra dermal, double intra dermal, ophthalmic tests in cattle and wattle test in case of poultry)
  • Gamma interferon assay, Gas liquid chromatography, PCR, ELISA for detecting circulating antibodies, FAT , LTT assays can also be used in the diagnosis

Control and prevention

  • Treatment and vaccination are inappropriate in control programmes for cattle.
  • In many countries, tuberculin testing followed by isolation and slaughter of reactors has been implemented as the basis of national eradication schemes.
Last modified: Monday, 4 June 2012, 5:01 AM