Can the primary infection cause illness due to spread of the infection within the lung?

Unfortunately, yes. Tuberculosis is a very unpredictable disease as there are a number of different ways that the primary infection can spread in the lungs:

  1. Usually the primary infection heals and does not spread, as the TB bacilli have been contained by the natural immunity. These children do not develop tuberculosis.
  2. In some children, especially those with a weak immune system, the body is unable to control the primary infection. The TB bacilli at the site of the primary infection multiply and spread to cause progressive lung infection (tuberculous pneumonia).
  3. TB bacilli may multiply in the regional lymph nodes, causing them to rapidly enlarge and compress the bronchus or trachea. Clinically this may present as wheezing or stridor with either collapse or hyperinflation of a lobe or the whole lung.
  4. The TB bacilli often remain dormant (inactive or ‘sleeping’) for many months or even years after the primary infection. The body has been able to control but not kill all the TB bacilli. If the child’s immune system later becomes weakened by malnutrition or another infection, such as HIV or measles, the TB bacilli may reactivate (multiply) and a local area of tuberculosis pneumonia will develop. Pulmonary tuberculosis due to reactivation of dormant TB bacilli may only present years after the primary infection. This is in contrast to progressive tuberculosis, which usually develops within the first year after the primary infection.
  5. ‘Adult type’ TB is usually seen in older children, especially adolescents. The area of tuberculous pneumonia may ‘break down’ and rupture into a bronchus. An infected lymph node can also erode into a bronchus. The TB bacilli can now spread along the bronchi to other parts of the lung. This occurs most commonly in the upper parts of the lung and results in an air filled cavity (a hole) containing caseous (dead) tissue which contains huge numbers of TB bacilli. This adult form of pulmonary tuberculosis (‘open tuberculosis’) is very infectious as many TB bacilli enter the airways. From here they are then coughed into the air where they may be breathed in and infect the lungs of other people. Adult pulmonary TB is usually the source of TB infection in children.
  6. Damage to the large airways by tuberculosis can result in bronchiectasis.
  7. Tuberculous infection may also spread into the pleura causing an effusion.
  8. Once the TB bacilli have spread beyond the primary infection (spread into the lung or enlarged lymph nodes) the child will become ill. Prompt diagnosis and urgent treatment is very important in these children with pulmonary tuberculosis.

The primary infection may spread to cause pulmonary tuberculosis.

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