tuberculosis

Tuberculosis:

Tuberculosis is a chronic bacterial infection, which causes more death world-wide than any other infectious disease. The bacteria Mycobacterium tuberculosis is spread through the air and usually affects the lungs, though some other organs are sometimes involved. Most who are infected with M. tuberculosis do not develop active tuberculosis. However, in weak immune systems, the chances are raised

With appropriate antibiotic therapy, most cases of tuberculosis can be cured, but drug-resistant strains are becoming more prevalent. Drug resistance occurs when the patient fails to take all of their medicine, thus the remaining strain grows resistant to the antibiotic. This may also occur if the patient is treated with too few drugs or small doses

During the nineteenth century, tuberculosis claimed more lives in the United States than any other disease. Improvements in housing, sanitation, and medicine reduced dramatically those numbers. By the 1980's the number of cases was little over twenty-two thousand. After 1985, however, the tides changed. The HIV/AIDS epidemic was one factor. This with weakened immune systems are vulnerable to reactivation of latent infection. Another cause is the increase of immigrants from countries where tuberculosis is more common. Increased poverty and drug use spread the disease. There has been poor compliance to treatment regimes, especially amongst disadvantaged groups, encouraging mutations and multi-drug resistant strains. The number of residents in long-term care facilities has increased. With age, the immune system declines, and latent infections become active

Tuberculosis is caused by repeated exposure to airborne droplets contaminated with the rod-shaped bacterium, M. tuberculosis. Sometimes, rarely, the bacteria is M. africanum or M. bovis. M. tuberculosis, like other mycobacterium, has an unusual cell wall, a waxy coating high in lipid count. Little is known about the membranes structure or function. This cell wall seems to allow the bacterium to survive in macrophage, cells of the immune system which ordinarily degrade invaders with enzymes. The coat also blocks many common drugs. Mycobacterium are called "acid fast", because their fatty cell walls prevent decolorization by acid solutions after staining for diagnostic procedures. M. tuberculosis is difficult to study in a lab environment. It multiplies slowly-- only once every twenty-four hours-- and they form clump, making working with and counting them difficult. It is airborne, and so can only be studied under very secure conditions

Only those with active tuberculosis can spread it, but the droplet nuclei remain airborne for long periods of time. They are small enough to bypass the defenses of the upper respiratory system, such as hairs and excretions of the mucosae. Infection begins when the bacterium reach the alveoli, where they multiply within macrophages. Those who have been undergoing treatment for at least two weeks are not usually infectious

The macrophages ingest the bacterium. Some are killed immediately, other multiply. Rarely, most time is HIV-sufferers and children, the infection spreads to other body sites, sometime resulting in life-threatening bacterial meningitis. During the two to eight weeks after infection, macrophages show pieces of the bacilli on the cells surface to other leukocytes, called T-cells. The T-cells release an elaborate set of chemical signals. The response it called cell-mediated hypersensitivity. This hypersensitivity will show the characteristic red welt in response to the tuberculin skin test (PDD test). Some T-cell signals produce inflammatory reactions. Others activate cells to kill bacterium and wall off infected macrophages in hard, grey capsules called tubercles. The immune system and the infection maintain a stand-off, sometimes for years. In the tubercles, tuberculosis bacilli may persist within the macrophages, but multiplication and spread is confined. Most undergo a complete healing of the initial infection. The tubercles calcify and become useless. A skin test and perhaps a chest x-ray my provide the only evidence of the struggle

Only about ten percent f people infected with the disease develop active tuberculosis. The risk is highest in the first year after the initial infection. Active tuberculosis results from the spread of bacterium from the alveoli through the bloodstream or lymphatic system to other parts of the lungs or lymph nodes. In about fifteen percent of cases, the bacterium cam travel to the skin, kidneys, bones, and reproductive or urinary systems. At the new sites, the body fights as before and kill the bacilli, but tissue is also killed. The dead cells and tissues form granulomas with the consistency of soft cheese, where the bacterium survive, though they do not flourish. Early signs of active tuberculosis may include weight lose, fever, sweats, and loss of appetite. As more tissue is destroyed and granulomas expand, cavities develop in the lungs, sometimes breaking the bronchi, allowing a large number of bacteria to escape when the sufferer coughs. As the disease progresses, the granulomas may liquify, perhaps the result of enzymes from the immune cells. The liquid is a rich growth medium for the bacteria, who multiply and spread quickly, creating further lesion and chest pain, coughing, and bloody sputum when a blood vessel is broken. Shortness of breath does not come until the lungs are extensively damaged

The skin test, or Montoux test, can identify most of those infected with tuberculosis. A substance known as purified protein derivative in injected hypodermically into the antibrachial and observed for 48 to 72 hours. A red welt is positive for infection, previous or current, active or not. If the test is positive, x-rays may show the lesions and cavities of active tuberculosis. Samples of sputum are also taken for cultures

Recently, researchers have developed a test utilizing nucleic acids to diagnose tuberculosis. Luminescent chemicals from fireflies are also being experimented with to find out what drugs may be used to kill the bacterium

The death rate among untreated tuberculosis sufferers is about fifty percent, but with treatment, that number can be taken down to ten. The drugs isoniazid and rifampin are given in tandem for or at least six months, and pyrazinamide for the first two. This is refereed to as short-course chemotherapy. Sometimes ethambutol is also given. A second line of drugs is often needed, with serious side effects, the treatment itself lasting from 18 months to two years

In parts of the world where tuberculosis is common, a weakened strain of it is given as a vaccine, which helps prevent spread, but does not stop the initial infection. It makes the skin test pointless, however, and is not used in the United States