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
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