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Flashcards in Respiratory Tract Infections: Tuberculosis Deck (13)

M. Tuberculosis

Infects 1/3 of global pop
8 million new cases each year
>2 million deaths per year
HIV has caused much of the recent increase



Mycobacterium tuberculosis causes TB,
Less commonly causes by M.bovis, M.africanum, M. Microts
M.tb most probably human adapted m.bovis
Have a resistant cell wall containing Mycotic acids-> resist destruction
Many harmless species in the environment
Obligate aerobes-> like tissues with high air conc
Facultative intra cellular pathogens-> infect mononuclear phagocytes
Slow growing-> 12-18h
Acid fast-> once stained resist decolorisation



Caused by mycobacterium leprae
Tuberculoid leprsoy-> common
Strong cellular immune response
Few bacilli lesions
Depigmented anaesthetic lesions
Lepromatous leprosy-> uncommon
Weak cellular immune response
Many bacilli in lesions
Thick granulomatous infections


Pathophysiology of m. Tuberculosis

Spread via airborne droplet nuclei-> can remain airborne for several hours-> inhaled-> lodge in alveoli->engulfed by macrophages
Slow replication and spread via lymph
In most individuals cell mediated immunity develops after 2-8 weeks
Activated T cells and macrophages form granulomas that limit infection spread-> bacterial cells which are sometimes viable remain here
Most individuals are asymptomatic and never develop the disease


Clinical features of TB

Non specific symptoms-> night sweats, fever, weight loss
Respiratory symptoms-> cough, shortness of breath, haemostatsis, chest pain
Mainly pulmonary-> extra pulmonary tends to be in HIV +


Other infection sites of TB

CNS-> meningitis
Skin/soft tissue-> most common-> cervical lymphadenitis
Bone and joints
Genitourinary tract-> prostatic, arcnitis, renal lesions, infertility in women, sterile pyuria (WBC in urine)
Disseminated disease-> many organs involved simultaneously, primary progressive or re activation of latent infection, millet seed lesions on CXR


Diagnosis of TB

Early diagnosis increases survival and prevents spread
Category 3 pathogen-> potential for lab acquired infection-> category 3 lab
Broncho alveolar lavage
Use Ziehl-Neelson stain


TB microscopy

Culture in lowenstein-Jensen-> slow 2-8 weeks-> beige, dry, rough calories
Rapid culture-> 1-2 weeks-> mycobacteria growth indicator tube


Antibiotic sensitive tests

Performed in a reference lab
-> Rifampincin, isoniazid, pyazinamide, ethambutol
Important to detect resistance especially in multi drug resistant (Rifampincin and isoniazid)
Extensively drug resistance -> tuberculosis that is resistant to Rifampincin, isoniazid and to any quinolone and at least one second line anti TB agent


Genomic tests for mycobacteria

DNA probes
Rapid detection of Rifampincin resistance
Typing methods to confirm outbreaks


Treatment of pulmonary TB

Initial phase-> 2 months of 4 drugs-> Rifampicin, isoniazid, pyrazinamide, ethambutol
Continuation phase-> 4 months of Rifampicin and isoniazid
If resistance suspected 5 drugs may be used initially with longer courses


Prevention of TB

Early diagnosis and treatment
-> usually non infectious after 2 weeks of therapy
Contact tracing and detection of latent infection
-> tuberculin skin test, chest radiograph, invitro interferon gamma release tests
Contacts treated if evidence of infection
Notifiable disease



Bacillus calmette-guerin
Live attenuated M.bovis
Main role is protecting children from severe disease
Efficacy is 70% in Uk

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