What does the Lepromin PPD test?
Lepromin PPD tests anti-leprosy immunocompetence, NOT exposure
tuberculoid = PPD + (why it’s called tuberculoid) = Strong immune response
lepromatous = PPD - = no immune response
T/F: The atypical mycobacteria are environmentally-acquired infections that cause neither TB nor leprosy.
How do atypical mycobacterial infections present?
Atypical mycobacterial infection in an immunocompetent adult is usually cutaneous; scrofula in children;
immunosuppressed hosts may have systemic symptoms, particularly from M. kansasii or MAI/C
What is the slowest growing human pathogen?
–no in vitro culture system,
slowest growing human pathogen,
prefers 30C to 37C
M. leprae has an extremely long incubation period, doesn’t transmit easily, only 5-10% of humans believed susceptible to disease
T/F: Atypical mycobacterial infections may be difficult to treat once established; require multiple antibiotics
How does M. leprae present (two forms)?
Hansen’s Disease (leprosy) presents on a range from:
Tuberculoid (paucibacillary, vigorous CMI both contains infection and damages nerves, PPD+) to Lepromatous (multibacillary, weak CMI, extensive cutaneous symptoms, PPD-)
Lepromatous easily tested by skin smear, biopsy, molecular probe, serology; PPD (-)
tuberculoid may be detected by biopsy or serology but sensitivity is low – physical exam, history, PPD (+)
When treating patients with M. Leprae, what sequelae can they develop?
Lepromatous patients when treated may develop erythema nodosum;
severe cases can require immunomodulant treatment like thalidomide (teratogen!)
How is leprosy treated?
Treat w/ 2yrs dapsone+rifampin
Describe the hematogenous spread of TB
Hematogenous spread by intracellular infection of naieve macrophages; activated ones clear it,
CD8 cells kill infected macrophages and establish caseating granulomas in which infection is contained.
TNF-alpha also important for containment
Eradication of TB seemed possible until?
Eradication seemed possible until AIDS
What is the acid fast staining procedure for TB?
Mycobacteria gram stain poorly, are acid-fast, very slow-growing
Acid fast staining procedure uses carbolfuchsin stain, acid/alcohol decolorization, and methylene blue counterstain; acid-fast (+)s hold carbolfuchsin during decolorization
Which strains of TB pose the greatest public health risk?
MDR and XDR strains are public health nightmares
What is the main TB transmission method?
Transmission is almost always to lung by inhalation, to lymph nodes, kidney, bones, CNS by hematogenous spread, to GI by swallowing infected sputum
How are TB infections combatted in the body?
Immunocompetent host raises strong CMI response, can hold infection latent for decades;
Immunosenescence or immunosuppression reactivates
What are the extrapulmonary symptoms of TB?
scrofula (fine needle aspirate),
genitourinary (intravenous urography, urine culture),
CNS (MRI, spinal tap), skeletal (MRI, joint fluid culture),
GI (Xray, CT of abdomen),
miliary (chest Xray w/ bright spotlight, lateral Xray, chest CT)
How should the incidence of TB be most effectively reduced?
The most helpful factors for reducing incidence of TB in a population are good diet & housing: latent cases are not contagious
How is TB treated?
Begin Directly Observed Therapy with 4-plus-drug courses featuring isoniazid; isolate patient for first two weeks.
What is the BCG vaccine?
for TB BCG vaccine (live attenuated M. bovis) is used abroad, not cost-effective here, can create weak-moderate false positive TST
How is TB diagnosed?
Acid fast staining procedure
Determine exposure by TST and/or IGRA, perform antibiotic resistance testing as soon as cultures grow (~2wks for cultures, another 3wks for resistance tests)
What are the classic TB symptoms?
Classic pulmonary TB (75%): cough, weight loss (“consumption”), fever, night sweats, hemoptysis, and chest pain, check sputum and chest Xray
Why should you culture TB from gastric secretions in children?
They are not strong enough to cough up sufficient sputum for testing.