51 - Mycobacterial Infections Flashcards
(20 cards)
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
Describe the lepromatous form of leprosy
- disfiguring skin lesions
- nodules and plaques
- absence / poor cell mediated - immune response
- skin test negative
- large numbers of organisms in tissues
Describe the tuberculoid form of leprosy
- milder form
- hypopigmented plaques or macules
- strong cell mediated immune response
- skin test positive
- few organisms present
How do you treat leprosy?
- multidrug regimen
- dapsone, clofazimine, and rifampin
What is the therapy for leprosy?
therapy last for years
- 1-2 years for tuberculoid
- 5 years for lepromatous
What is important to remember about treating TB?
It is essential that at least two active antituberculosis agents always be used to treat active TB to prevent the emergence of drug resistance during therapy.
