---
-------------
13. Tubercuosis (TB) is caused by a rod-shaped bacterium known as Mycobacterium tuberculosis.
Transmission
TB is transmitted by droplet infection. Infected persons spread the disease by coughing. When a second person inhales the infected aerial droplets, the bacteria enter the lungs and become active.
TB may also be transmitted via infected cattle through their milk. Pasteurization effectively removes this transmission route.
Effects
As the infection begins, phagocytes move to the areas of infection in the lung. They ingest the bacteria via phagocytosis. The bacteria survive this ingestion and begin to reproduce. The lung then surrounds these infected phagocytes with small rounded swellings known as tubercles. The infection remains in the lungs and slowly becomes less severe. If re-infected, the disease becomes chronic, gradually destroying lung tissue. As the infection continues, a fever develops, the person loses their appetite and a persistent cough develops, one that may entail coughing up blood. In later stages, the chronic infection spreads to the lymph nodes, bones and gut. Death may ensue soon after.
---
-------------