Respiratory tract infection: TB

what is the cause of recent increase in TB cases in developing countries?

HIV infection

what bacteria causes TB in humans?

Mycobacterium tuberculosis

what causes TB in cattle?

M. bovis

other important species of mycobacteria

Tuberculoid leprosy - common

strong cellular immune response.

few bacilli in lesions.

depigmented anaesthetic lesions.

lepromatous leprosy - uncommon

weak cellular immune response.

many bacilli in lesions.

thick, granulomatous lesions.

why is M.tuberculosis known as acid fast bacilli?

once stained the cells resist decolourisation.

where does mycobacteria tuberculosis grow?

in tissues with a high O2 content (such as the lungs)

what does mycobacterium tuberculosis infect?

mononuclear phagocytes (e.g. macrophages)

how is TB spread?

airborne droplet nuclei

droplets inhaled, lodge in alveoli and organism is taken up by alveolar macrophages.

how fast does TB replicate and where does it spread to?

slow replication and spread to hilar lymph nodes.

when does cell mediated immunity develop after infection?

2-8 weeks after.

how do WBC defend body from TB?

- T lymphocytes and macrophages form granulomas that limit further replication.

- bacteria remain in the centre.

- necrotic caseating granuloma - lung tissue in the middle dies.

tuberculosis caseous granuloma

non specific symptoms of TB?

fever, weight loss, night sweats

respiratory symptoms of TB?

cough

shortness of breath

haemoptysis

chest pain

what are cavitating lesions?

where the lung tissue has been destroyed by the granuloma leaving cavities.

most serious complication of TB?

central nervous system disease - TB meningitis and space occupying lesions.

what is disseminated disease?

many organs involved simultaneously - may result from primary progressive disease or reactivation of latent infection

other sites of TB infection?

skin and soft tissue.

bone and joints.

genitourinary.

disseminated disease.

what is Potts disease?

vertebral TB - destroys disc space.

what is miliary TB?

Large number of organisms can invade the bloodstream and spread to all organs. The involvement of many organs - disseminated.

what category of infection is TB?

3 - pathogen potentially laboratory required action

how to get a sample from someone with TB?

sputum

bronchoalveolar lavage.

pus/tissue

urine

cerebrospinal fluid.

what is bronchoalveolar lavage?

bronchoscope introduces a measured amount of fluid that is then collected and examined.

What is Zeihl Neelsen Stain used for?

diagnose TB.

rapid, cheap, simple and robust.

what other stain is used in TB diagnosis?

auramine - can be confirmed with ZN

how to take a culture of TB bacteria?

slow.

needs Lowenstein Jensen slopes in shatter proof glass containers.

what kind of colonies does mycobacterium tuberculosis form?

beige, dry and rough colonies.

can cause cauliflower/verrucose colonies.

how to take rapid cultures of M tuberculosis?

liquid media - Kirchners liquid.

automated system - mycobacteria growth indicator tube

what is extensively resistant TB defined as?

resistant to any member of the quinolone family (rifampicin and isoniazid).

one second line anti TB agent - kanamycin, capreomycin, amikacin.

Genomic tests for mycobacteria

PCR

DNA probes

rapid detection rifampicin resistance.

whole genome sequence.

initial treatment of TB?

2 months of 4 drugs.

rifampicin.

Isoniazid.

pyrazamide

ethambutol

continued treatment of TB?

4 months of rifampicin and isoniazid

resistance treatment of TB?

5 drugs used initially - longer course and second line agents.

How to prevent TB?

early diagnosis and treatment.

contact tracing and detection of latent infection (skin tests, chest radiography, in vitro interferon gamma release test)

contacts treated in infection evidence.

vaccination for TB?

BCG - bacillus Calmette Guerin

live attenuated M.bovis strain