Tuberculosis

Question 1

Mycobacterium Tuberculosis
• Structure
• Transmission
• Replication Cycle
• Disease Presentation
• Pathogenic Mechanism
• Epidemiology
• Treatment
• Mortality
• Key findings/Diagnosis

Answer 1

​Structure
Obligate aerobe, Acid Fast Bacillus

Transmission
Aerosols generated by coughing people who have the disease. Adequacy of cell mediated immunity determines if you will get infected.

Replication Cycle
Very slow doubling time (18 hours)

Disease Presentation
90% of people who are infected do not develop disease in these people the only evidence of infection is a fibrocalcific nodule at infection site. 3 presentation types.

1. Primary TB - resembles typical pneumonia, Lobar infiltrates etc.
2. Miliary TB - Seeds on CXR, Liver pain, Bone marrow and spleen involvment. Pott’s disease, Sterile pyuria, hematuria, proteinuria, Epididymitis, prostatitis, Adrenal insufficiency.
3. Secondary TB - weight loss, low grad fever, pleuritic pain, night sweats Secondary activation occurs at Apices of the lung and may involve cavitation.

Pathogenic Mechanism
Cord factor is found ONLY in virulent strains and inhibits macrophage maturation and induces TNF-alpha release. Sulfatides (surface glycolipids) also inhibit phagolysosomal fusion. Once ingested by macrophages PknG prevents phagolysosome fusion. T cell recognition and stimulation by IL-12 from macrophages leads to CD4 => TH1 maturation and release of IFN-gamma which activates macrophages. Activated macrophages release TNF-alpha to recruit more monocytes.

Epidemiology
AIDS, Prison, Immigrant, Alcoholism, TNF-antagonists, Diabetes, etc.

Treatment
RIPE

Mortality
not mentioned

Key findings/Diagnosis
Dx: Lowenstein-Jensen agar, NO growth on blood agar, PCR + on smear positive specimens = extremely likely there is MTB infection

Less likely to see MTB in sputum of HIV patients because immune system is needed for the cavitation that causes + sputum smears