TB Flashcards
What stain is used to identify TB?
Ziehl-Neelson stain
Pink/red slender TB bacilli
Describe the cell wall of TB
Contains peptidoglycan and complex lipids
But will not gram stain
Why can a gram stain not be used to identify TB?
Waxy coating on cell surface makes cell impervious to gram staining
What MO causes TB?
Mycobacterium tuberculosis
What are the most prevalent species of TB?
M tuberculosis
M bovis
M africanum
Discuss the transmission of TB
By respiratory droplets = coughing, sneezing
Infectious dose = 1-10 bacilli
In what setting is TB most likely to spread?
Close proximity institutions = prisons, dense living conditions
Outline the pathogenesis of TB
1) inhaled infectious droplets
2) engulfed by macrophages
3) local lymph nodes
4) forms primary complex = ghons focus + draining LN (5% progress to primary disease, tissue damage)
5) initial containment of infection
6) latent infection
Then either 1) reactivation, post primary TB, 2) cures (95%)
What is the most important immune response against TB, and why?
Cellular response (T cells)as Tb has infected the macrophages = intracellular
Who is very at risk of TB?
HIV pts = don’t have the immune response to control the infection
How can TB be divided?
Primary
Post-primary
Latent
Discuss the characteristics latent TB
Inactive, contained tubercle bacilli in body
TST/IFN +ve
Chest x-ray normal
Sputum smears/cultures -ve
No symptoms
Not infections
Discuss the characteristics of TB disease
Active multiplying tubercle bacilli
+ve TST
Abnormal CXR
Sputum smear/cultures +ve
Symptoms = cough, fever, weight loss
What is TST?
Tuberculosis sensitivity test
Mantoux
Screening for TB
Intradermal TB Ag injection
False +ve = BCG, non TB
What is an IFN test?
Detection of Ag specific IFN-gamma prod
Cannot distinguish latent and active TB
What is a ghon focus/complex?
Lesion in the lung consisting of calcified focus of infection and an associated LN
What is post-primary TB?
Reactivation Or exogenous re-infection
What are the risk factors for the reactivation of TB
Infection with HIV
Substance abuse
Prolonged therapy with corticosteroids
Immunosuppressive therapy
TNF-alpha antagonists
Organ transplant
DM
On histology what is the typical appearance of TB?
Caseating granuloma
Lymphocytes fused to form giant cells
Inflam cells
Caseous necrosis centre
What sites of the body can become effected by TB?
Pulmonary = lungs
Extra-pulmonary = larynx, LN, pleura, brain, kidneys, bones/joints
Miliary (uncontrolled bacterial spread) = all parts via bloodstream
What are the risk factors to make you suspect TB?
Recent migrants/non-uk born
HIV
Homeless
Drug users
Close contacts
What are the symptoms of TB?
Fever
Night sweats
Weight loss and anorexia
Tiredness and malaise
Cough (most common)
Haemoptysis occasionally
Breathlessness if pleural effusion
What are the signs of TB?
Fever
Weight loss
Often no chest signs despite CXR abnormality
Lung crackles
Extensive disease = signs of cavitation, fibrosis
Signs of effusion
Which investigation would be performed when TB is suspected?
CXR
3 morning sputum samples = solid/liquid cultures, ZN staining
Induced sputum = when pt cant bring up sputum
Bronchoscopy = tube into lungs, flush with saline, send fluid to lab (bronchi-alveolar lavage)
NAAT = nuclear acid amplification test, rapid result within a day
Drug resistant testing
Histology
