51 - Mycobacterial Infections Flashcards
What are the mycobacterial diseases?
1 - Mycobacterium tuberculosis
Tuberculosis (TB)
2 - Mycobacterium avium complex (MAC) infections
- Pulmonary
- Disseminated
3 - Mycobacterium leprae
Leprosy
Describe the characteristics of mycobacteria
- Rod shaped
- May form filaments
- Lipid-rich cell walls (mycolic acids)
- Gram-stain poorly or not at all
- Acid-Fast Stain***
- Can replicate in macrophages
- Generally slow-growing
dormancy within granulomas (TB)
Describe the disease characteristics of M. tuberculosis (TB)
- Transmission through respiratory droplets.
- Primary disease is pulmonary.
- May become disseminated, particularly in immuno-suppressed patients.
- Most (~90%) infected individuals have latent infections (NOT active, NOT symptomatic)
Describe the symptoms of active TB
- general malaise
- fatigue
- fever
- chills
- night sweats
- wasting
- pulmonary insufficiency
- cough
- bloody sputum
Describe latent TB
- Inactive, contained tubercle bacilli in the body
- TST or blood test (IFN-g release) results usually positive
- Chest x-ray usually normal
- Sputum smears and cultures negative
- No symptoms
- Not infectious
- Not a case of TB
Describe active TB in the lungs
- Active, multiplying tubercle bacilli in the body
- TST or blood (IFN-g release) test results usually positive
- Chest x-ray usually abnormal
- Sputum smears and cultures may be positive
- Symptoms such as cough, fever, weight loss
- Often infectious before treatment
- A case of TB
What is it important to differentiate latent from active TB?
You choose different drugs for latent and active TB
What are the obstacles of TB treatment?
- Organism grows slowly
- Hard to kill when slow
- Organism remains viable but dormant
- Slow metabolism
- Rapid development of resistance
- Toxicity (non-compliance)
What are the solutions to TB treatment obstacles?
- Regimens must contain multiple drugs to which the organism is susceptible.
- Combination therapy
- 3-4 drugs usually, long-term
- Drugs must be taken regularly.
- Drug therapy must continue for sufficient time.
- Direct observed therapy
What are the 5 different drug classes we will focus on today for TB?
- Isoniazid
- Rifamycin (rifampicin, rifabutin)
- Pyrazinamide
- Ethambutol
- Streptomycin
Describe the M. avium complex (MAC)
Includes
- M. avium
- M. intracellulare
- Others
What can MAC cause?
Can cause pulmonary disease in immuno-competent individuals, and disseminated disease in AIDS patients.
How is MAC acquired?
Acquired through the ingestion of contaminated food and water
- Primary method
- Organisms found in the environment
Acquired through respiratory droplets.
How common is leprosy?
- 300,000 cases globally
- less than 100 cases in U.S. each year.
- develops over decades
What are the two forms of leprosy?
- Lepromatous form
- Tuberculoid form
