Mycobacteria - Bacterial Disease

Mycobacteria

·        Classification:

o   Tuberculosis complex: M. Tuberculosis and M. Bovis

o   Other mycobacteria: M. Avium-Intracellulare (MAC), M. Kansasii, M Marinum

o   Leprosy: M. Leprae

·        Resulting Diseases:

o   Tuberculosis Complex

§  Immunocompetent: In descending frequency: lung, lymph nodes, kidney, genital tract, CNS 

§  Immunodeficient: Lung in > 70%, but extra pulmonary involvement > 70% in blood (25 – 40%), lymph nodes, faeces, CNS due to ¯cell mediated immunity

o   MAC:

§  Immunocompetent: Kids – cervical lymphadenitis, adults: chronic destructive lung disease (uncommon) 

§  Immunodeficient: Infection common. Initial colonisation of GI tract, then spread to blood, lymph nodes, liver, spleen, less lung involvement but invariably fatal

§  Most strains of MAC are resistant to standard anti-mycobacterial drugs

·        Drug treatment: 

o  Standard drugs: Rifampicin, Isoniazid, pyrazinamide, ethambutol. Normally first 3, except if from Pacific Islands where use all 4 due to ­isoniazid resistance. Rifampicin is the best, if resistant to this then poor prognosis 

o  Most strains of M Bovis are resistant to pyrazinamide 

o  Many strains of M Tb from AIDS patients in the US (especially NY) are resistant to Rifampicin and Isoniazid

o  Other anti-mycobacterial drugs: ciprofloxacin, clarithromycin, amikacin, rifabutin, clofazimine

·        Vaccination: BCG:

o  Live vaccine 

o  Indicated for high risk infants: household has individuals from endemic areas of with past or current Tb 

o  Neonatal BCG is 60 – 90% protective for extra-pulmonary Tb and 65% for pulmonary Tb. Protection lasts 10 – 15 years

o  Adverse effects:  local abscess in 1%.  Treated conservatively.  Some require excision