Mycobacteria Flashcards
Describe TB’s role in human history
major human disease for 5000 years, consummately adapted to infect humans
What major disease halted the progress toward eradication of TB?
AIDS
What strains of TB represent the greatest challenge to public health?
MDR and XDR
What are some characteristics of mycobacteria?
gram stain poorly, acid-fast, slow growing
Describe the key features of acid fast staining
carbolfuschin stain, acid/alcohol decolorization, and methylene blue counterstain; acid-fast (+) should hold carbolfuschin stain upon decolorization
How does transmission of TB work?
inhalation–>lung–>lymph nodes–>kidney–>bones–>CNS by homogenous spread—>GI by swallowing infected sputum
Why isn’t TB a much more serious disease?
Immunocompetent host raises strong CMI response, can hold infection latent for decades;
What are key factors for reactivation of TB?
Immunosuppression or immunosenecence
What is the mechanism for pathogenesis?
Hematogenous spread by intracellular infection of naive macrophages; activated macrophages clear the infection, CD8 cells kill infected macrophages and establish caseating granulomas in which infection is contained; TNF-alpha, also important for containment
What are the symptoms for classic pulmonary TB? What is the prevalence of it?
cough, weight loss (consumption), fever, night sweats, hemoptysis, and chest pain (75%)
How is pulmonary TB diagnosed?
check chest x-ray and sputum
What two things are critical for TB granuloma formation?
CD8 and TNF-alpha
What does it mean when extrapulmonary manifestations occur?
usually reactivstions of disease
What are common extrapulmonary sites for TB?
scrofula in neck, genitourinary, CNS (meninges or abcesses), skeletal (long bone or spine), GI (very rare for now), miliary
In the case of pediatric patients keep in mind
that the infection must have been recently acquired (trace sources) and watch for miliary and meningitis
How do you determine TB exposure?
by TST or IGRA
When selecting treatment for TB:
perform antibiotic resistance testing as soon as culture grows
How long does it take to carry out antibiotics resistance testing?
2 wks for cultures, 3 weeks for resistance testing
Describe TB’s treatment process
begin directly observational therapy with 4-plus drug courses featuring isoniazaid; isolate patient for the first 2 weeks
What is the major drug used to treat TB?
Isonizaid
Why don’t more people get the vaccine for TB?
BCG vaccine is used abroad, but is not cost-effective here and can create weak-moderate false positives
What are the best ways to minimize incidence of TB?
Good diet and housing, latent cases are not contagious
what is the TB vaccine? why is it problematic for those who are immunosuppressed?
BCG (live attentuated M. bovis), it will cause those who are immunosuppressed to become ill
What are atypical mycobateria?
environmentally acquired infections that cause neither TB nor leprosy
