Respiratory Tract Infections: Tuberculosis Flashcards
Mycobacteria
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
Hydrophobic
Acid fast-> once stained resist decolorisation
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
Leprosy
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 Sputum Broncho alveolar lavage Pus/tissue Urine CSF 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
PCR
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
Vaccination
Bacillus calmette-guerin
Live attenuated M.bovis
Main role is protecting children from severe disease
Efficacy is 70% in Uk