Mycobacterial diseases Flashcards
Does mycobacteria have cells wall
– Unusual waxy cell wall- high lipid content
– Slow growing- different media required
3 stains which are commonly used in mycobacterial testing
– Acid fast bacilli (AFBs)
– Ziehl Neelsen (ZN)
– Phenol auramine.
what happens in the latent phase of a mycobacterial infection.
– Mycobacterium ingested by macrophages but it cannot be killed so it multiples inside
common types of mycobacterium and the infections they cause
• M. Tuberculosis complex: Tuberculosis
– M. Tuberculosis
– M. Bovis- common in animals.
• M. Leprae Leprosy
• “Atypical” Mycobacteria:
– M. Avium complex- HIV associated
– M. Kansasii
– M. Marinum- Fish tank granuloma
what chronic infection id M. tuberculosis often seen with
HIV
how is TB acquired
droplet spread, inhalation
most common site of TB infection within the lung
periphery of lung mid zone.
What is ghon focus
swollen lymph nodes and found in midzone.
What immune cell plays a major role in TB
macrophages- phagocytoze macrophages but cannot kill it
they then migrate to the lymph nodes
what is the body’s response to a tubercle formation
– Granuloma
– Cell - mediated immune response- not antibody.
– Central area of epithelioid cells, giant cells.
– Surrounding lymphocytic cell infiltration.
– Central area caseous necrosis.
– Fibrosis / calcification of lesions
– Bacilli slowly die / may remain viable 20 years
what are the symptoms found in primary TB
Influenza - like” syndrome- fever and malaise.
what can be seen in the chest x-ray in primary TB
nothing
what does the tuberculin skin conversion test show in primary TB
normal initially and then 3 months after infection will be positive.
what happens in secondary TB
reactivation of TB
lowered immunity
what factors cause the immunity to become compromised which results in secondary TB
– Malnutrition
– Alcoholism
– Debilitating illness
– HIV infection- knocks out T cells so immune system is weak.
– Silicosis, chronic renal failure, gastrectomy..
– Anti TNFα blockade (e.g. infliximab)- TNF maintains granuloma wall containing all the bacteria within it.
Where is the most common site to find reactivated TB
• Lung apices
most common symptoms of TB
Haemoptysis
• Weight loss, fever, night sweats.
what happens to the granuloma/tubercle in secondary TB
cannot maintain granuloma/tubercle so TB spreads.
what extra pulmonary sites can be affected by TB
– Pleura – Lymph nodes – Kidneys , epididymis – Bone- spine – Intestines- from swallowing sputum or drinking unpasteurized milk. – Brain / meninges – Pericardium
common symptoms of Tb associated meningitis.
– Unidentified fever
– Personality change
– Focal neurological deficit- this is were the bacteria multiply.
• Basilar inflammation.
– Mild headache / meningism.
– May lack constitutional quartet
• (fever, night sweats, anorexia, weight loss)
how is TB diagnosed
– Radiology-Chest X – ray- lesion in upper lung.
– Histology
– Skin testing
– (Blood test: Interferon- γ release assay: IGRA)
– Microbiology.
• Confirmation of diagnosis
• Drug sensitivities.
• Molecular typing profile: “MIRUs”.
• “Fresh” samples / tissue: i.e. NOT formalin fixed as it kills the organism.
How are sputum tests for TB given
3 “Early Morning” specimens.
How can sputa be used for testing if there is a lack of it. What can be done to obtain some other form of aspirate.
– Induce sputa by nebulised saline- irritates patient and makes them cough.
– Bronchial aspirates
– Gastric aspirate- young children don’t cough up sputum they swallow it so wash lignin of intestine and send the sample.
what is the composition of CSF be like in
– Protein will be high
– Glucose will be low
– Microscopy /culture
Treatment for TB
- 2 months- Isoniazid, rifampicin, pyrazinamide ethambutol / (streptomycin)- all in one tablet
- 4 months- Isoniazid, rifampicin
Treatment for meningitis induced by TB
corticosteroids
Mantoux test
- Purified Protein derivative (MTB extract)- derived from TB and injected under the skin
- Cell mediated response
- Read @ 48-72 hours
Interferon gamma release assays
• Blood tests: – Immunological: • Specific T-cells: IFN γ production. – TB specific antigens (ESAT6, CFP10) • DON’T cross-react with M bovis BCG.
prevention of TB
BCG vaccine.
2 clinical forms of leprosy
– Tuberculoid- immune system is dealing with it.
• Macules / plaques- skin leison
• Nerve: ulnar, common peroneal
– Lepromatous- immune system not dealing with it.
• Subcutaneous tissue accumulation.
• Ear lobes, face - leonine facies.
treatment for TB
– Dapsone, rifampicin, clofazimine
