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Pathology => Human Diseases => Pneumonia
Pneumonia
Pneumonia, term applied to any of about 50 distinct inflammatory diseases of the lungs characterized by the build up of fluid in the lungs. Pneumonia is caused by infection from bacteria, viruses, rickettsia, mycoplasma, fungi, or protozoa.
Before the advent of antibiotics, the most common cause of death in adults was lobar pneumonia, an acute infection caused by the pneumococcus, a bacterium formally known as Streptococcus pneumoniae. The pneumococcus usually attacks an entire lobe or portion of a lobe of the lung; in double pneumonia, it attacks both lungs. Pneumococcal lobar pneumonia often occurs in winter, after an acute, viral upper respiratory infection. Usual symptoms include a shaking chill followed by a fever of about 40° C (about 104° F), pain in the chest on breathing, a cough, and blood-streaked sputum.
Most other types of bacterial pneumonias are bronchopneumonias, which differ from lobar pneumonia in that they affect regions of the lung close to the bronchioles (small bronchial tubes). Bronchopneumonias may be caused by pneumococcus, Klebsiella pneumoniae,Haemophilus influenzae,Legionella pneumophilia (which causesLegionnaires' disease), or various staphylococci and streptococci bacteria. The onset of bronchopneumonia is less rapid than lobar pneumonia and the fever is lower.
Most forms of bacterial pneumonia can be effectively treated with antibiotics. A vaccine is available that confers immunity against the most virulent forms of pneumococcus. It is given to people over the age of 50 and to those with chronic heart, lung, or liver disease.
Pneumonia is also caused by many different viruses, including those that cause upper respiratory infections, such as the influenza virus, adenoviruses, and rhinoviruses. Most cases of viral pneumonia are usually mild and resolve spontaneously without specific treatment.
One common type of pneumonia, formerly called primary atypical pneumonia, is caused by Mycoplasma pneumoniae, a tiny prokaryotic organism (a single-celled organism that lacks a distinct nucleus) that is neither a bacterium nor a virus. Epidemics of mycoplasma pneumonia occur in schools and in the military. The disease usually resolves spontaneously, but treatment with antibiotics can be helpful.
Pneumonia due to Pneumocystis carinii, a normally harmless protozoan, is the most common cause of death in people with acquired immune deficiency syndrome (AIDS), and can also occur in people with leukemia or others with impaired immune responses.
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