Tuberculosis Flashcards
What bacteria causes TB
Mycobacterium tuberculosis
How is TB spread
Infection occurs when tiny droplets containing the bacteria are inhaled into the lungs (from cough/sneeze), droplet infection
How do the bacteria become dormant
Bacteria taken up by phagocyte and survive and replicate inside the phagocyte, usually immune system seals off the infected phagocytes in lungs in tubercles where they become dormant and person shows no obvious symptoms, after 3-8 weeks infection controlled and infected region of lung heals
How does TB become active
Dormant bacteria may become reactivated and overcome the immune system if immune system cannot initially contain the disease when it first arrives/it the immune system no longer working properly
When is reactivation of TB bacteria more likely
In people with weakened immune systems eg people with AIDS, the old or very young, malnutrition and poor living conditions
Sequence of symptoms of TB
-initial symptoms are fever, severe coughing, loss of weight causing by inflammation of lungs
-damages the lungs as progresses and can cause respiratory failure as bacteria multiply rapidly and destroy lung tissue creating holes (granuloma- lesions)
-can spread to other parts of body
Why can the M. tuberculosis bacteria survive inside macrophages
Because they have very thick waxy cell walls which makes them very difficult to break down
How do TB bacteria target the cells of the immune system
Can suppress T cells which reduces antibody production and attack by T killer cells
Why does a person infected with TB experience fever
As part of the inflammatory response fever-causing substances are released from macrophages and neutrophils which affect the hypothalamus and alter the set point for the core body temp to a higher temp= enhances immune function and phagocytosis, bacteria may reproduce more slowly
What is glandular TB
When TB bacteria moved to infect other parts of the patient’s body with the main symptom being enlarged lymph glands(infected lymph nodes), can also move to infect bones and CNS
How is TB diagnosed
-skin test (injected with tuberculin under skin of forearm, positive result shows inflamed area of skin due to antibodies already being present, can give negative result for latent TB/false positive if had BCG vaccine)
-blood tests which identify T cells specific to antigen occurring on M. tuberculosis
-coughed up sputum cultured to see what bacteria present
-chest X rays to discover extent of damage
How do TB bacteria infect macrophages
Engulfed by macrophage, bacteria inhibits lysosomes meaning lysozymes cannot be released and bacteria not digested, have thick waxy outer layer which protects them from attack and lie dormant in tubercules sealed off, disrupts production of cytokines and the apoptosis of the macrophage which usually happens after invasion
