Tuberculosis Flashcards
what us tuberculosis
mycobacteria infection that is spread in air
occurs in many body sites
what type of reaction occurs in TB
Delayed Type IV hypersensitivity (granulomas with necrosis)
T cell response (NOT antibody response
in TB is the damage to the lung due to the bacteria or the T cell response
T cell response
why can TB be described as immunity + hypersensitivity
immunity: enhanced macrophage killing
hypersensitivity: Type IV granulomatous inflammation, tissue necrosis and scarring
4 bacteria that cause TB
Mycobacterium tuberculosis
mycobacterium bovis
mycobacterium africanum
mycobacterium microti
how is mycobacterium tuberculosis presented on a. Gm stain
rod shaped Gm=ve bacillus
what people are more likely to get TB
immunocomprimised
what test is used to diagnos mycobacterium tuberculsosis
zeihl-Neelson
what opportunistic pathogens cause TB in immunocompromised individuals
Virus (CMV)
bacterium (mycobacterium avium intracellulare)
Fungi (aspergillus, candida pnumonocystis)
Protozoa (cryptosporodoa, toxoplasma)
In TB infection does/does not mean disease
does not
infected people can still be healthy
1/3 of people are infected
2 types of TB
active (5-10% get sick, 8 weeks to present)
latent (lies dormant in body)
what determines TB’s clinical outcome
immune response
what is the immune response to TB
1) Tb evades phagocytosis
2) Slow onset Th1 adaptive immunity: 8 week
3) enhanced effector mechanism (MTB-sepcitid CD4+ T cells, IFN-y, TNF-a)
4) granuloma (walled off infection
what is the characteristics of TB
caseous necrosis
granuloma forms, growing collection fo phagocytic cells that bacteria infects and replicates in
little oxygen so bug adapts and lies dormant then reactivated with patient is old, immunosuppressed, on steroids
what type if immunity occurs in TB
Th-1 biased immunity
what factors have contributed to the global TB rise
HIV pandemic Displacement & migration Poverty Disruption to health infrastructure from political changes / conflict Poorly managed TB programmes Anti-TB dug resistance: MDR
risk factors for TB
contact with TB infected person (TB in sputum)
immigrants from Africa/India
poverty, homelessness, alcoholism
HIV
what happens to patients with open (contagious) TB
positive smear test = kept in hospital
how is positive TB classified
first exposure and up to 5 years later
what type of reaction occurs in primary TB
Delayed Type IV sensitivity reaction
what are the characteristics of Primary TB
Small focus (ghon focus)
Peripheray of mid zone of lung
Large hilar nodes (granulomatous)
what is the most common type of TB
latent TB
re-infection or re-activation
what causes re-acivation of TB
Age
HIV
immunosuppressive therapy eg. steroids
characteristics of secondary TB
at apices of lung (upper lobe)
Fibrosing + Cavitating apical lesions
Similar to cancer
Large increasing in size
what type of TB are people with chronic kidney disease likely to suffer from
latent TB
increased risk of treatment toxicity
dialysis
what is given to reduce the risk of active infection to some people with latent TB
chemoprophlaxis
what people are more likely to get TB
people born in other countries migrate to country where it is less common (secondary TB) deprivation immunocomprimised young adults & elderly more in men silicosis
symptoms of TB
productive cough occasional haemoptysis night sweats fever weight loss can affect different organs pleuritic pain jaundice meningitis GI pain/bowel obstrcution spinal pain cold absess pericardiac tamponade renal failure hypoadrenalism
where is latent TB more likely to occur
it is asymptomatic wakes up in parts of lung where more oxygen
in patients with septic arthritis and TB symptoms what are never injected into solitary arthritic joints
steroids incase it is TB
what is primary lymph node TB
- Common in kids
- Pneumonia associated
- Extrathoracic (most common) nodes
- Firm, non-tender enlargement of a cervical or supraclavicular nde
- Node = necrotic, can liquefy
- No abscess formation/no erythema
if a patient is diagnosed with TB what other test should be carried out
HIV test
how is TB diagnosed in examination
upper zone crackles
swollen lymph glands
what test is carried out to check for TB in bronchial washings
Zeihl Nelson Stain
how can samples be collected from TB patients
sputum
bronchial washings
drain pleural effusions
needle in cold absess
what does an X-ray of a patient with TB show
consolidation pleural effusion thickening of mediastinum (hilarious adenopathy) cavity formation fibrosis upper lobe predominancy bulky lymph nodes scarring/shrinkage heals with calcification
what is ghon focus - seen on chest x-ray of TB patient
Small calcified nodule in upper parts of upper lobe or lower parts of upper lobes (midzone)
what causes the unilateral calcification as seen in patients with Tb
emphysema
pus in airways
what Is milary TB
person has poor immune controlled spread everywhere in lung + blood + to CNS
tree in bud
how is milary TB usually diagnosed
blood culture
bronchoalveolar lavage fluid: smear negative, culture positive
lumbar puncture checks CNS involvment
if no sputum produced how should a sample be collected
bronchoscopy from upper Lobe
what test is done on samples in suspected Tb
zeihl-neelson (misses Tb 50% of time) detects mycobacterium
auramine via microscopy
what is the most important test on samples from suspected TB
culture
drug sensitivities
solid/liquid phases
latent TB is culture negative/positive
negative
what does nucleic acid amplification detect
TB mycobacterium and non TB mycobacterium
high specificity
identifies MDR
what test is carried out on the skin
Mantoux (tuberculin test)
detects previous exposure to TB and BCG
takes 2 days
Type IV sensitivity reaction
what can the Mantoux test not distinguish
the type of TB
what would give a false negative In the Mantoux test
immunosuppressed - HIV infection
sarcoidosis
drugs - chemo, anti-TNFs, steroids
what would give a false positive in the Mantoux test
BCG vaccine
non-tuberculosis mycobacterium
what test is more effective at diagnosing TB than the mantoux test
IGRA
take blood, 1 visit
detects T cell secretion of IFN-y following exposure to M.tuberculosis specific antigens
high sensitivity and specificity (does not react with BCG)
detects all TB types
what tests for active TB
PCR: primary TB test answer in 90mins/2hours spit or cartage sensitivity of 3 samples (90% affective) misses 1 in 4
other than TB detection what is else does PCR tell us
if organism is resistna two rifampicin
how is TB treated
BCG vaccine
Anti-TNF drugs given
cured in 6 months
do not give patients steroids/immunosuppressants
what drugs are given for active TB treatment
4 drugs for 2 months: Rifampicin, Isoniazid (H), Pyrazinamide, Ethambutol
2 drugs for further 4 months:
Rifampicin + Isoniazid
if TB is in the brain/CNS how long should treatment last
4 drugs for 2 months
2drugs for 10 months
side effects of Anti-TB drugs
Need to stop the pill Liver problems Hepatitis (common) Vomiting nausea (most common) Lack of appetite Arthralgia Cutaneous reactions Cutaneous hypersensitivity Retrobular neuritis (colour blindness blindness)
side effect of Rifampicin
pink/orange urine/sweat/tears
induces cytochrome enzyme (rapid steroid breakdown eg, contraception and breakdown of opiate analgesics)
why is isoniazid prescribed with pyridoxine
to prevent B6 deficiency/polyneuropathy
allergic reactions with hepatitis: skin rashes/fever
side effects of ethambutol
optic neuritis: reversible colour blindness
side effects of pyrazinamide
hepatic toxicity
side effect of stretomycin
Irreversible damage to vestibular nerve in elderly/those with renal impairment
Only used if MDR/very ill
what is DOTS: Directly Observed Therapy Short-Course
for people who lead chaotic lifestyles/unlikely to take medication
responsible observer administers drug and observes ingestion
what TB is not treated in UK
latent TB due to low transmission rates, treated in USA
treatment for latent TB
2 drugs, 3 months: Rifampicin, Isoniazid or 1 drug 6 months: isoniazid
treat prior to immunosuppressive therapy
other treatments: Furoquniolones and TMC207 (bedaquilline)used if resistant to everything else
what is MDR-TB
multi drug resistant TB
resistant to first line therapy: Rifampicin + Isoniazid
common in Russia/estonia/china
must stay in hospital
how long do patients with MDR-TB need to take medication for
2 years
what treatment is given to patients with Isoniazid resistance
need to take drug for another 3 years
what is XDR-TB
resistant to second line therapy
MDR + Fluquinolones + injecables
prognosis of Tb
global epidemic, kills most people as single pathogen
5-10% risk of infection
HIV carry 10% extra TB risk each year
what is TB diagnosis confirmed by
PCR
AAFB
Culture
what people should you suspect TB in if the symptoms are present
returning travellers
immunocompromised
non-resolving pneumonia
