Mycobacterial Infections

Question 1

Tuberculosis (Mycobacterium tuberculosis hominis, M. bovis)

Answer 1

• Spreads by aerosols from person to person, enters into the lungs
• Forms GHON COMPLEX lesions in lungs (area of infection + lymph nodes) - contains caseous granuloma (necrotizing center) / hilar lymphadenopathy,
• Most cases of primary TB are asymptomatic. In progressive cases (kids, immunocompromised, homeless) non specific symptoms (fever, night sweats, weight loss, fatigue).
• Secondary TB (reactivation or reinfection) - T-cells are already familiar with antigen and cause necrosis and cavities in lungs. Same as primary symptoms + hemoptysis. Disease may disseminate (miliary) and become fatal.
• Todays treatment - long term antibiotics.

Question 2

Leprosy (Mycobacterium leprae)

Answer 2

-Spreads person to person through intimate contact - respiratory tract or open wounds
-Proliferates in areas of lower body temperature (hands and face)
-Infection occurs in 5% of exposed people and is either tuberculoid or lepromatous
Tuberculoid = Moderate: few lesions, dermal granulomas with sensory loss (not caseous). Reflects appropriate TH1 activation
Lepromatous = Severe: foamy macrophages act as incubators and form globi. Form diffuse, tumor like lesions of skin, eyes, testes, nerves, lymph nodes and spleen–claw shaped hands, saddle nose. Results from deficient TH1 activation.

Question 3

Mycobacterium avium-intracellulare Complex (MAI)

Answer 3

• Spreads by aerosols from infected water (or infected food, soil)
• Immunocompromised older people (⅓ of AIDS patients!). COPD predisposes.
• Begins in lungs - causes TB like pulmonary cavities and caseating granulomas (but slow progressing)-years to decades. Macrophages engulf (but dont kill) bugs, then spread throughout body
• Antibiotics may control but not cure.

Question 4

Atypical Mycobacteria

Answer 4

• Not common, may be inhaled, ingested, or inoculated
• M. kansasii - granulomatous disease similar to MAI in older people
• M. scrofulaceum - granulomatous, cervical lymphadenitis in young children
• M. marinum - granulomatous or pyogenic, localized skin lesions - from water (pools)
• M. chelonae or fortuitum - painless abscesses from trauma that ulcerate and then heal