Flashcards in Infection: Mycobacterium Tuberculosis Deck (15):
How is tuberculosis diagnosed?
Cant be gram stained so use acid fast staining instead - it is a bacillus
Tuberculin skin test
Does mycobacterium tuberculosis grown fast or slow?
Very slow growing - the generation time is 15-20hrs - therefore culture can take 2 - 12 weeks
What is the mode of transmission of mycobacterium tuberculosis?
How contagious is TB?
Via respiratory droplets - coughing, sneezing, speaking. Casual contact is not enough for transmission - need prolonged exposure eg family members, homeless, prisons
Why is mycobacterium tuberculosis not phagocytosed by alveolar macrophages?
It has a cell wall with a high lipid content which prevents fusion of the phagosome to the lysosome.
It can even multiply inside alveolar macrophages
What is the treatment for TB?
R ifampicin (makes urine orangey red)
Because TB is slow growing it is a prolonged course (6months - 2 years) therefore need to closely monitor compliance. If taken correctly 90% cure rate
What is latent TB and how can it progress?
Latent infection is where there are live bacilli but they are dormant - not multiplying.
From latency 95% of cases will self cure and the other 5% will become post primary TB (the bacilli start multiplying).
What are the main differences between latent TB infection and TB disease?
Latent TB is not a case of TB - there are no symptoms, normal xray, sputum negative. However there is a strong immune response.
TB disease is infectious, has abnormal xray and there are symptoms.
What are the risk factors for latent TB being reactivated to post primary TB infection?
- Infection with HIV is the highest risk (therefore all cases of TB are tested for HIV)
- immunosuppressive therapy
- diabetes mellitis
How can pulmonary TB spread to become miliary TB? (whole body)
Can spread directly, through the blood stream or via lymphatics
What are the common symptoms for pulmonary TB?
Fever, weight loss, night sweats, malaise
Cough (most common) may be heamoptysis and breathlessness if pleural effusion
What is the appearance of the chest Xray in someone with pulmonary TB?
ill-defined patchy consolidation
Can get cavitations
May have pleural effusion
What is the tuberculin sensitivity test?
Used to diagnose latent TB
Tuberculin is injected intradermally and read 48-72 hours later - the swelling should be measured (not the redness)
Looking for a strong immune response
TB is a notifiable disease, what does this mean?
The doctor making or suspecting a diagnosis of TB is legally responsible to notify public health so they can begin screening of close contacts.
How can TB be prevented?
BCG vaccine - a live vaccine therefore cant be given to HIV pts.
Given to babies in high prevalence communities - 70-80% effective at preventing severe childhood TB.