Tuberculosis


Tuberculosis
A highly contagious infection caused by the bacterium called Mycobacterium tuberculosis. Tubercles (tiny lumps) are a characteristic finding. Diagnosis may be made by skin test, which if positive should will be followed by a chest X-ray to determine the status (active or dormant) of the infection. Although there are millions of new cases of TB each year, not everyone exposed to the bacterium becomes infected nor does everybody infected with it develop clinical symptoms of TB. A genetic region has been discovered to be associated with clinical TB. People with at least one high-risk copy of this genetic region are ten times more likely to develop TB than normal. The genetic region contains a gene, NRAMP1, that is known to be involved in the susceptibility to leprosy, which is caused by a bacterium related to TB. Tuberculosis is also more common in people with immune-system problems, including AIDS. Treatment of active tuberculosis is mandatory by law in the US, and should be available at no cost to the patient through the public health system. It involves a course of antibiotics and vitamins that lasts about six months. It is important to finish the entire treatment, both to prevent reoccurrence and to prevent the development of antibiotic- resistant tuberculosis. Most patients with tuberculosis do not need to be quarantined, but it is sometimes necessary.
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A specific disease caused by infection with Mycobacterium t., the tubercle bacillus, which can affect almost any tissue or organ of the body, the most common seat of the disease being the lungs. Primary t. is typically a mild or asymptomatic local pulmonary infection. Regional lymph node s may become involved, but in otherwise healthy people generalized disease does not immediately develop. A cell-mediated immune response arrests the spread of organisms and walls off the zone of infection. Infected tissues and lymph node s may eventually calcify. The tuberculin skin test becomes positive within a few weeks, and remains positive throughout life. Organisms in a primary lesion remain viable and can become reactivated months or years later to initiate secondary t.. Progression to the secondary stage eventually occurs in 10–15% of people who have had primary t.. The risk of reactivation is increased by diabetes mellitus, HIV infection, silicosis, and various systemic or malignant conditions, as well as in alcoholics, IV drug abusers, nursing home residents, and those receiving adrenocortical steroid or immunosuppressive therapy. Secondary or reactivation t. usually results in a chronic, spreading lung infection, most often involving the upper lobes. Minute granulomas (tubercles), just visible to the naked eye, develop in involved lung tissue, each consisting of a zone of caseation necrosis surrounded by chronic inflammatory cells (epithelioid histiocytes and giant cells). These lesions, which give the disease its name, are also found in other tissues (lymph nodes, bowel, kidney, skin) to which the disease may spread. Rarely, reactivation results in widespread dissemination of tubercles throughout the body (miliary t.). The symptoms of active pulmonary t. are fatigue, anorexia, weight loss, low-grade fever, night sweats, chronic cough, and hemoptysis. Local symptoms depend on the parts affected. Active pulmonary t. is relentlessly chronic and, if untreated, leads to progressive destruction of lung tissue. Cavities form in the lungs, and erosion into pulmonary blood vessel s can result in life-threatening hemorrhage. Gradual deterioration of nutritional status and general health culminates in death due to wasting, infection, or multiple organ failure. Variant syndromes (tuberculous lymphadenitis in children, severe systemic disease in persons with AIDS) are caused by organisms of the Mycobacterium avium-intracellulare complex. [tuberculo- + G. -osis, condition] In 1993 the World Health Organization (WHO) declared t. a global emergency. Fully one-third of the world's population is infected with TB. On a global scale, TB ranks first among infectious diseases as a cause of death. Two-thirds of all the world's cases are in Asia, but the disease is also endemic in parts of Africa and other regions. War and social upheaval have played a role in the spread of t. beyond endemic zones; prevalence of infection is higher among refugees and immigrants. One-third of all persons with t. in the U.S. were born outside the country. From the 1950s, when antibiotics began to be used for the treatment of t., until the 1980s, the incidence and mortality of the disease declined steadily in the U.S. During the 1980s the incidence began to rise because of many new cases in persons with AIDS and because of increasing prevalence of multidrug-resistant strains of M. t.. Since 1993 the figures have again declined, chiefly because of improvements in t. prevention and control programs in state and local health departments as a result of increased federal funding provided to states. At least one-third of persons with AIDS contract t., and t. is the cause of death in one-third of persons who die of AIDS. Since antibiotic resistance in M. t. has been a growing problem for years, multidrug regimens, usually including isoniazid, rifampin, and pyrazinamide, are standard. Other drugs, such as ethambutol, streptomycin, kanamycin, and capreomycin, may be added or substituted. The success of treatment is limited not only by the resistance of organisms to several agents but also by the risk of severe toxic effects with all the standard agents. Unlike most infections treated with antibiotics, t. requires not days or weeks of treatment, but months and years. Long-term compliance tends to be poor among mobile, indigent, and uneducated persons. According to WHO, the principal reason for the spread of multidrug-resistant strains of M. t. is ineffectual management of t. control programs, particularly in third-world countries. An inappropriate or unfinished course of chemotherapy not only leaves the patient still sick and still contagious, but favors the selection of resistant bacteria. It is estimated that 50 million of the world's cases of t. involve multiply resistant tubercle bacilli. Currently WHO urges that t. programs worldwide adopt the practice of directly observed therapy (DOT), in which a health care worker observes each patient swallowing each dose of medicine. In a study performed at several U.S. centers, DOT for t. was found to be cost-effective when the cost of relapses and treatment failures was added to the cost of self-administered therapy, even though the raw cost of DOT was higher. U.S. public health authorities have established as a national goal the elimination of TB (defined as an incidence of <1 case per 1 million population) by 2010.
- adult t. SYN: secondary t..
- aerogenic t. infection with the Mycobacterium t. spread by inhalation of infected droplets.
- arrested t. SYN: inactive t..
- attenuated t. a mild chronic form marked by caseous tubercles of the skin and the occurrence of cold abscesses.
- basal t. t. of the basilar portions of the lungs.
- cerebral t. 1. SYN: tuberculous meningitis. 2. cerebral tuberculoma.
- childhood t. initial (primary) infection with Mycobacterium t., characterized by pneumonic lesions in the middle parts of the lungs, rarely cavitary, with rapid spread to lymph node s in hilar and paratracheal areas; more often seen in childhood, but the pattern is not limited to children.
- childhood type t. SYN: primary t..
- cutaneous t. pathologic lesions of the skin caused by Mycobacterium t.. SYN: t. cutis.
- t. cutis SYN: cutaneous t..
- t. cutis orificialis any tuberculous lesion in or about the mouth or anus.
- t. cutis verrucosa a tuberculous skin lesion having a warty surface with a chronic inflammatory base seen on the hands in adults and lower extremities in children, with marked hypersensitivity to tuberculous antigens. SEE ALSO: postmortem wart. SYN: tuberculous wart.
- disseminated t. SYN: miliary t..
- enteric t. a complication of cavitary pulmonary t. usually resulting from expectoration and swallowing of bacilli that then infect areas of the digestive tract where there is relative stasis or abundant lymphoid tissue; can be caused by ingestion of bovine tubercular organisms in infected milk, now rare. SEE ALSO: tuberculous enteritis.
- exudative t. a stage of infection with Mycobacterium t. causing severe edema and cellular inflammatory reaction without much necrosis or fibrosis.
- generalized t. SYN: miliary t..
- healed t. a scar or a calcified, fibrous, or caseous nodule in the lung pleura, lymph node, or other organ, resulting from previous t. that has regressed. If truly healed, no organisms are present and reactivation is not possible.
- inactive t. a fibrous or nodular area of previously active t. that has regressed, with the lesion having remained stable for a long period; can be calcified; reactivation is possible. SYN: arrested t..
- miliary t. general dissemination of tubercle bacilli in the blood, resulting in the formation of miliary tubercles in various organs and tissues, and occasionally producing symptoms of profound toxemia. SYN: disseminated t., generalized t..
- open t. pulmonary t., tuberculous ulceration, or other form in which the tubercle bacilli are present in the excretions or secretions; in the lung, usually the result of cavity formation.
- t. papulonecrotica SYN: papulonecrotic tuberculid.
- postprimary t. SYN: secondary t..
- primary t. first infection by Mycobacterium t., typically seen in children but also occurs in adults, characterized in the lungs by the formation of a primary complex consisting of small peripheral pulmonary focus with spread to hilar or paratracheal lymph node s; may proceed to cavitate or heal with scarring or may progress. SYN: childhood type t..
- pulmonary t. t. of the lungs.
- reactivation t. SYN: secondary t..
- reinfection t. SYN: secondary t..
- secondary t. t. found in adults and characterized by lesions near the apex of an upper lobe, which may cavitate or heal with scarring without spreading to lymph node s; theoretically, secondary t. may be due to exogenous reinfection or to reactivation of a dormant endogenous infection. SYN: adult t., postprimary t., reactivation t., reinfection t..

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tu·ber·cu·lo·sis t(y)u̇-.bər-kyə-'lō-səs n, pl -lo·ses -.sēz a usu. chronic highly variable disease that is caused by a bacterium of the genus Mycobacterium (M. tuberculosis) and rarely in the U.S. by a related mycobacterium (M. bovis), is usu. communicated by inhalation of the airborne causative agent, affects esp. the lungs but may spread to other areas (as the kidney or spinal column) from local lesions or by way of the lymph or blood vessels, and is characterized by fever, cough, difficulty in breathing, inflammatory infiltrations, formation of tubercles, caseation, pleural effusion, and fibrosis called also TB

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n.
an infectious disease caused by the bacillus Mycobacterium tuberculosis (first identified by Koch in 1882) and characterized by the formation of nodular lesions (tubercles) in the tissues.
In pulmonary tuberculosis - formerly known as consumption and phthisis (wasting) - the bacillus is inhaled into the lungs where it sets up a primary tubercle and spreads to the nearest lymph nodes (the primary complex). Natural immune defences may heal it at this stage; alternatively the disease may smoulder for months or years and fluctuate with the patient's resistance. Many people become infected but show no symptoms. Others develop a chronic infection and can transmit the bacillus by coughing and sneezing. Symptoms of the active disease include fever, night sweats, weight loss, and the spitting of blood. In some cases the bacilli spread from the lungs to the bloodstream, setting up millions of tiny tubercles throughout the body (miliary tuberculosis), or migrate to the meninges to cause tuberculous meningitis. Bacilli entering by the mouth, usually in infected cows' milk, set up a primary complex in abdominal lymph nodes, leading to peritonitis, and sometimes spread to other organs, joints, and bones (see Pott's disease).
Tuberculosis is curable by various combinations of the antibiotics streptomycin, ethambutol, isoniazid (INH), rifampicin, and pyrazinamide. Preventive measures in the UK include the detection of cases by X-ray screening of vulnerable populations and inoculation with BCG vaccine of those with no immunity to the disease (the tuberculin test identifies which people require vaccination). There has been a resurgence of tuberculosis in recent years in association with HIV infection. The number of patients with multidrug resistant TB has also increased due to patients not completing drug courses. Many centres have introduced direct observed therapy (DOT) with nurse practitioners to administer drugs.

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tu·ber·cu·lo·sis (too-bur″ku-loґsis) 1. any of the infectious diseases caused by species of Mycobacterium and characterized by tubercle formation with caseous necrosis in the tissues. The usual causative species are M. tuberculosis and M. bovis. Tuberculosis occurs in various different animal species and can vary widely in its manifestations, with a tendency to long chronicity. Any organ may be affected, but in humans the lung is the major seat of the disease (see 2. pulmonary t.) and is the usual portal of entry into the body. See also nontuberculous mycobacteria, under mycobacterium. pulmonary t.

Medical dictionary. 2011.

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