Tuberculosis. Coloured axial computed tomography (CT) scans of sections through the chest of a 36 year old with pulmonary tuberculosis (TB). The front of the body is at top, the lungs are dark blue with affected areas lighter blue. Pulmonary TB is caused by the bacterium Mycobacterium tuberculosis, which is spread by coughing and sneezing. The bacteria create primary tubercules, nodular lesions of dead tissue and bacteria, when inhaled into the lungs. Pulmonary TB may be symptomless, and may recur at periods when the patient's immune system is weakened. Symptoms of the active disease include fever and coughing up of blood. Treatment is with long-term antibiotics.