Mycobacterial Diseases Flashcards
What is the microbiology of mycobacteria?
Non motile, rod shaped
Long chain fatty acids, complex waxes and glycolipids in cell wall - structural rigidity, compete freunds adjuvant potent necrotising factor, staining characteristics
Acid alcohol fast, hold onto zn stain and auramine which has higher sensitivity
Where can NTM be identified?
Remote streams, shower head, whirl pool (pseudomonas), fish tank (marina)
Soil, ubiquitous
Varied pathogenicity
No person to person transmission
Resistant to classical anti TB drugs
Can colonise
Use clarithromycin and drugs used for mdr TB
What are the slow growing NTM?
MAI- aka m avium complex, in immunocompetent may invade bronchial tree, pre existing bronchiectasis or cavities. In immunocompromised- disseminated infection
M marinum- swimming pool granuloma
M ulcerans- skin lesions eg bairnsdale ulcer, buruli ulcer, chronic progressive painless ulcer. Surgical debridement
What are the rapidly growing NTM?
Abcessus, chelonae, fortuitum
Skin and soft tissue infections
In hospital settings
Respond to erythromycin and doxyclyin
What are the risk factors for NTM?
60/70’s, airways disease, previous TB eg cavities, asthma, bronchiectasis, complement deficient, cf, cancer
What is the diagnosis for NTM?
Lung disease- pulmonary symptoms, opacities, multifocal bronchiectasis
Exclusion of other diagnoses
Positive culture of more than one sample
Positive BAL
Positive biopsy with granulomata
What is treatment for NTM?
Susceptibility testing may not reflect clinical usefulness
MAI- clari, azithryomycin
Rifampcin
Ethambutol
+/- amikacin, streptomycin
Rapid growing NTM- macrolide based 18-24 months
What is m leprae?
Paucibacillary tuberculoid- cell response is huge, peripheral neuropathy
load of bacteria and cell mediated immunity
Multibacillary lepromatous- lumps and bumps
Lateral eyebrow loss, thickened nerve?
Still common
What is mtb?
Multi system disease
2nd most common cause of death by infectious agent after HIV
Most common opportunistic infection in HIV
7 closely related species, tb, bovis resistant to pyrizinamide, africanum
Obligate anaerobes, generation time 15-20 hours
What are the TB disease States?
Exposed individual Active TB quickly (2years) HIV Uninfected Cleared infection, natural immunity Contained- majority of 3rd of people who have TB, lifetime risk of activation. Mantoux test- induration not erythema
How is TB transmitted?
Droplet nuclei/airborne Less than 10microm particles Suspended in air Reach lower airway macrophages Infectious dose 1-10 bacilli 3000 infectious nuclei- cough, talking 5 mins Air remains infectious for 30 mins
How can TB be prevented?
Detection of cases
Treatment of index case
Prevention of transmission- Personal Protective Equipment, negative pressure isolation
Optimisation of susceptible contacts- vaccination 70-80% effectiveness in preventing severe childhood TB, protection wanes
Inflixumab- TB cases TNF link/immunocompromised link
What is the natural history of TB?
Primary- asymptomatic, ghon focus complex
Limited by CMI
Rare allergic reactions include erythema nodosum
Occasionally disseminated
Latent
Reactivation
Why would you get post primary TB?
Failure of cell mediated immunity, immune system wanes 30 years old
Immunosuppression, chronic alcohol excess, malnutrition, ageing
Pulmonary or extra pulmonary
How can the host response shape clinical outcome?
Less effective immune response >> Healthy context- ltbi Lymphadenitis Localised extrapulmonary Pulmonary localised/widespread- caseating granulomata, upper lobe Meningeal Miliary
