The bacteria, lodging in the mucous membranes of the throat, secrete a potent toxin, which causes tissue destruction and the formation of a gray membrane in the upper respiratory tract that can loosen and cause asphyxiation. The toxin may also spread via the blood and damage tissues elsewhere in the body. Diphtheria can be prevented by vaccination. Pneumonia is an acute infection of one or both lungs that can be caused by a bacterium, usually the pneumococcus bacterium, virus, fungus, or other organism. Symptoms include high fever, pain in the chest, difficulty in breathing, coughing, and sputum.
Viral pneumonia is generally milder than the bacterial form.
Pneumocystis carinii pneumonia, which is caused by a parasitic protozoan, generally only occurs in patients whose immune system is suppressed, as in AIDS or leukemia. Antibiotics are used to treat bacterial pneumonia and have greatly reduced the mortality rate of the disease. Tuberculosis is a contagious disease caused by the bacterium Mycobacterium tuberculosis , identified by Robert Koch in 1882. Also known as TB and consumption, the disease primarily affects the lungs, although the intestines, joints, and other parts of the body may also become infected. Symptoms as the disease progresses include fever, weakness, loss of appetite, and, in the pulmonary form, cough and sputum.