It is the year 1900, and a young man falls ill, suffering from a shaking chill, sharp chest pain, cough, fever, and headache. These warning signs sound the alarm--he has pneumonia. At that time, in the days before antibiotics, it was often a fatal disease, killing thousands of people, especially during epidemics. Pneumonia--the two primary types being bacterial and viral--isacute infection of the air sacs inside the human lungs. It usually starts inthe airways or bronchi and spreads to one or both lungs. Today, when treatedproperly, most people recover from bacterial pneumonia; however, it remains the sixth most common cause of death among older people in the United States.The very young and very old are especially likely to fall victim to pneumonia, the most common form of which is caused by Streptococcus pneumoniae--bacteria that are transmitted through the air and inhaled into the lungs. These bacteria cause pneumococcal disease, which results not only in pneumonia,but can also attack blood cells causing an infection called "bacteremia," and the brain, causing meningitis. An extremely safe and effective vaccine--one injection lasts most people a lifetime--protects against almost all bacteria which cause pneumococcal diseases. Staphylococcus bacteria will alsocause pneumonia, as will certain viruses, protozoa, and even fungi. Only bacterial pneumonia can be effectively treated with antibiotics.

The treatment used to prevent pneumonia in the days before antibiotics is attributed to Almroth Edward Wright, an English bacteriologist and a pioneer inthe infant field of immunology. Near the end of the nineteenth century, Wright became interested in developing inoculations using killed bacteria. These acted as vaccines, causing a mild infection that triggered future resistance to the bacteria. Wright first developed a vaccine against typhoid fever in thelate 1890s. In 1911 he went to South Africa where he was asked to help prevent pneumonia among workers in the gold mines. There he developed an inoculation against pneumonia based on the same principles he had used to formulate the typhoid vaccine. His inoculation greatly reduced the number of pneumonia cases. Between 1926 and 1934, another Englishman, Frederick Griffith, developedlaboratory techniques for classifying over thirty different strains of bacteria. At around the same time, Rebecca Craighill Lancefield, an American doctor, was working on a similar project identifying streptococcus bacteria. Finding out more about disease-causing bacteria was the focus of much medical research on both sides of the Atlantic. The race was on to come up with the causeand cure for many life-threatening diseases, including pneumonia.

By the 1930s other researchers were working on a new class of wonder drugs--antibiotics. Using Griffith's early classification work, Oswald T. Avery, a Canadian-American physician, as well as other bacteriologists such as AlphonseDochez, made a discovery which would prove important to the science of genetics. As they studied two strains of the pneumococci bacteria, they recognizedthat one had a smooth coat--the S strain--and the other--the R strain--was without a coat, giving it a rough appearance. The R strain seemed to be missingan enzyme that would aid the bacteria in forming its carbohydrate coat. Avery and others found that when living R strain bacteria were added to extractsfrom the S strain, the R became S--that is, the R strain could replicate thecoat and appear smooth. Most scientists thought that a protein from the S strain caused this reaction. However, in 1944, Avery and others demonstrated that the trigger was pure DNA (deoxyribonucleic acid). It became clear that DNAwas the important compound in carrying traits in living things. This discovery opened the way for the exploration of the structure and behavior of DNA, astudy which is fundamental to modern genetics. Around the time of Avery's discovery, the antibiotic penicillin was past the stage of trial usage and was being used to cure pneumonia among World War II soldiers as well as civilians.Today, penicillin is still the drug of choice in treating bacterial pneumonia. In severe cases, patients are placed on ventilators to aid breathing and clear the lungs of sputum.

Another form of pneumonia, Legionnaire's disease, is caused by Legionellapneumophila bacteria and is usually treated with the antibiotic erythromycin. Nonbacterial causes of pneumonia include viruses such as the influenza virus, adenovirus, and even the chicken pox virus. In viral cases, antibioticsare sometimes administered because the lungs are often infected by bacteriasimultaneously. In recent years there has been an upsurge in the number of pneumonia cases caused by Pneumocystis carinii, a protozoan. This type of pneumonia is often associated with persons having an immunological deficiency such as that brought on by the AIDS virus. Treatment includes an aerosol misting of the lungs with antibiotics.

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