Tuberculosis. X-ray of the chest of a patient after recovery from tuberculosis (TB). Pulmonary tuberculosis is caused by the bacterium Mycobacterium tuberculosis, which is spread by coughing and sneezing. The bacteria create primary tubercles, nodular lesions of dead tissue and bacteria, when inhaled into the lungs. These nodules have become hardened by calcium deposits (centre left, white). Pulmonary tuberculosis may be symptomless, and may recur at periods when the patient's immune system is weakened. Symptoms of the active disease include fever, weight loss and the coughing up of blood. Treatment is with long- term antibiotics.