Flashcards in Mycobacterial Diseases Deck (24):
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)
No person to person transmission
Resistant to classical anti TB drugs
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 biopsy with granulomata
What is treatment for NTM?
Susceptibility testing may not reflect clinical usefulness
MAI- clari, azithryomycin
+/- 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?
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?
Active TB quickly (2years) HIV
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?
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
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
Pulmonary localised/widespread- caseating granulomata, upper lobe
What is the presentation of extra pulmonary TB?
Lymphadenitis- scrofula, cervical lymph nodes,abscess and sinus
GI- swallowing of tubercles (lavage in kids)
Peritoneal- ascitic or adhesive looks like crohns
Genitourinary- slow progression to renal disease, subsequent spreading to lower urinary tract sterile pyuria
Bone and joint- haematogenous spread, spinal TB venous plexus nearby, potts
Military- seeds on cxray, progressive disseminated haematogenous TB, increasing due to HIV
Meningitis- Africa and Vietnam
What is the clinical approach to TB?
High index of suscpicion
Ix culture and histology
Preventing onward transmission
What should be included in hx and examination?
Ethnicity, travel, contacts with TB, bcg vaccination, non specific examination findings
What investigations are needed for TB?
Cxr mediastinal, para tracheal stripe widened
Sputum times 3
Bronchoscopy, biopsies, emu
NAAT- PCR point of care
Tuberculin skin test- mycobacteria, relies on lots of things, delayed hypersensitivity, cross reacts with bcg
Igra- detection of antigen specific ifn gamma production, enzyme linked immune asay. Cannot distinguish latent and active
What is the smear in TB involving?
Gastric aspirates in kids
Other specimens centrifuged urine and csf
Rapid, operator dependant
What is the treatment for TB?
Rifampcin- raised transaminases and induces cytochrome p450 , orange secretions
Isoniazid- peripheral neuropathy, hepatotoxicity
Ethambutol- visual disturbance
RI for 4 months Dot/vot
What is mutli drug resistant TB?
Resist to r and I
Extremely drug resistant- fluoroquinolones and at least one injectable
Spontaneous mutation and inadequate treatment
Previous TB, HIV, known contact to mdr TB, 4 months positive smear, 5 months positive culture
4/5 drug regimen
What are the challenges in TB and HIV diagnosis?
Clincal history- less likely to be classical, symptoms absent in low cd4 count
Chest X-ray- more likely extrapulmonary, x Ray changes variable
Smear microscopy and culture- less sensitive
Skin test- more likely to be negative
Timing of tx