Tuberculosis is a serious infectious disease caused by the rod-shaped bacteria, Mycobacterium tuberculosis, which lodge in the lungs and destroy lung tissue. Sometimes called consumption, or simply TB, tuberculosis is usually transmitted from person-to-person by infected airborne droplets as the bacteria have no means of locomotion on their own. Once the bacteria invade the lungs, the body's immune system sends out white blood cells which build walls of fibers around the bacteria to keep them confined, forming small, hard lumps known as a "tubercles." Once the body has formed tubercles to encapsulate the bacteria, the primary infection may be contained and, although the person will always test positive for the TB bacteria, the disease itself may not develop. Later in life, if the walls containing the germs are broken down, the lungs once again become infected. If the immune system is initially unsuccessful in walling off the germs, a full case of TB develops, new bacilli grow and multiply, and the lung tissue actually dies and becomes soft. Liquid from the tissue is coughed up leaving a cavity in the lung. Cavities may have already formed before a person even notices symptoms such as a cough or fever. Eventually, however, coughing becomes painful and brings up blood with the lung tissue. By this time, the case is well advanced. If large areas of the lungs are damaged, breathing becomes difficult and the body fails to deliver the necessary oxygen to tissues. The bacilli may spread to other tissues of the body causing secondary infections and complications. If untreated, the person will die. If treated with antibiotics and other drugs, the patient may recover, usually over a period of time.
Tuberculosis is not easy to diagnose from symptoms because the cough and fever brought on by the disease may be dismissed as cold symptoms. During a routine checkup, physicians commonly administer a skin test for TB, usually a tine test that has multiple needles which inject a small amount of tuberculin derivative. If a person has ever been infected by TB bacteria, the skin around the injection area will become hardened within 48 hours and other tests, such as a sputum analysis and chest X-ray to detect spots on the lung caused by the formation of tubercles, may be performed to confirm a positive diagnosis.
TB's disease-causing bacteria were discovered by a German physician, Robert Koch in 1882, who also invented the first diagnostic test for tuberculosis. Working in a small laboratory next to his doctor's office, Koch experimented with many types of bacteria, even taking pictures of them through a microscope his wife gave him as a gift. Koch first took interest in the livestock disease, anthrax. In 1876, he showed by painstaking experiments that a specific bacteria caused the disease.
A few years later he turned his attention to tuberculosis which, in the latter part of the nineteenth century, was responsible for one in seven deaths. In 1881, he began working with tissue taken from an ape that had died of tuberculosis, isolating the rod-shaped bacteria by growing it in culture dishes separate from any other germs. He then inoculated healthy guinea pigs with the TB bacteria. The guinea pigs became sick and Koch observed the tuberculosis bacteria growing in them. He then removed some bacteria from the infected guinea pigs and grew them in yet another culture. Finally, he infected a second group of healthy animals with this cultured bacteria. When those animals contracted TB, he could be sure that the same bacteria were responsible. This involved procedure (known as Koch's Postulates) soon became the standard method in which disease-causing organisms could be positively identified.
In 1890, Koch discovered that a substance released from the TB bacteria caused an allergic reaction in people who have been exposed to TB. This substance, called tuberculin, was isolated from heat-killed cultures of TB bacteria. Koch used this phenomenon to develop a simple test for TB in which a small amount of tuberculin was administered under the skin of the upper arm. If hardening or inflammation occurred, the body already had antibodies working against TB, indicating the person had previously been exposed to the bacteria.
Around the time of the Koch's discovery, the only treatment for tuberculosis was bed rest, sometimes in a healthful sanitarium. In 1921 however, two French microbiologists, Albert Calmette (1863-1933) and Camille Guerin (1872-1961), developed a successful vaccine. From 1906 through 1921 the two had cultured tubercle bacilli from cattle finding that, over many generations, they had developed a strain that was avirulent--in other words, it no longer caused TB. They tested an even weaker strain, known as Bacillus Calmette-Guerin (BCG), on human subjects and found it had few ill side effects yet bestowed immunity against TB. The BCG vaccine gained wide acceptance in France, Canada, and Asia in the 1920s and 1930s, but was more controversial in the United States and Great Britain where physicians questioned its effectiveness. The BCG inoculation consisted of live bacteria bred to be avirulent, whereas many other vaccines are from heat-killed attenuated microorganisms. In the United States, the vaccine is given only to people who risk coming in contact with the disease. Since the late 1940s and the age of antibiotics, tuberculosis has been treated with drugs, the first effective drug being streptomycin. Two standard drugs used today are isoniazid and rifamprin, alone or with other drugs administered over a long period of time because the lungs are slow to heal.
Once controlled by inoculation and antibiotics, at least in North America and Europe, tuberculosis is now believed to be spreading at an alarming rate, particularly in many developing nations. Deaths from TB number about three million annually, or 9,000 people every day, and The World Health Organization has declared that the disease will claim more than 30 million lives within the decade if immediate action is not taken.
Multiple Drug Resistant tuberculosis (MDR-TB), one factor in the increase of cases, is caused either by too short a treatment time, patients taking their drugs improperly, or treatment with the wrong medication. If MDR-TB is present, the patient is treated with several different drugs at once. MDR-TB usually causes death within a few weeks in people suffering from HIV/AIDS. The increase in the incidence of TB has also paralleled the rise of the AIDS epidemic. Because a weakened immune system does not respond to the usual TB tests, an "anergy panel" must be performed, particularly for people with HIV/AIDS. If there is no response to this test, X-rays are ordered to detect infection and begin treatment as soon as possible to help prevent the infection from progressing into the disease stage. In 1996, a new sputum test called the "Mycobacterium Tuberculosis Direct Test" was developed which detects TB within four to five hours as opposed to the usual one to eight weeks required for the usual tests, allowing for prompt treatment.
This is the complete article, containing 1,141 words
(approx. 4 pages at 300 words per page).
