TuberculosisFrom Wikipedia, the free encyclopediaJump to: navigation, searchTuberculosisClassification & external resourcesChest X-ray of a patient suffering fromtuberculosisICD-10 A !"-A #"ICD-9 $$-$%OMIM &$'#(%DiseasesDB %!!MedlinePlus $$$$'' 000624eMedicine med)*+*(emerg)&% radio)(MeSH C01.252.410.040.552.846Tuberculosis ,abbreviated as TB for tubercle bacillus or Tuberculosis- is a common and deadly infectious disease caused by mycobacteria, mainly Mycobacterium tuberculosis" .uberculosis most commonly attacks the lungs ,as pulmonary ./- but can also affect the central nervous system, the lymphatic system, the circulatory system, the genitourinary system, bones, 0oints and even the skin" 1ther mycobacteria such as Mycobacterium bovis, Mycobacterium africanum, Mycobacterium canetti, and Mycobacterium microti can also cause tuberculosis, but these species do not usually infect healthy adults"231ver one-third of the 4orld5s population has been e6posed to the ./ bacterium, and ne4 infections occur at a rate of one per second"2*3 7ot everyone infected develops the full-blo4n disease8 asymptomatic, latent ./ infection is most common" 9o4ever, one in ten latent infections 4ill progress to active ./ disease, 4hich, if left untreated, kills more than half of its victims":n *$$(, mortality and morbidity statistics included ("& million chronic active ./ cases, %"# million ne4 cases, and "& million deaths, mostly in developing countries"2*3 :n addition, a rising number of people in the developed 4orld are contracting tuberculosis because their immune systems are compromised by immunosuppressive drugs, substance abuse, or 9:;)A: of ./ cases being resistant to standard treatments and *> resistant to second-line drugs"2(3 ./ incidence varies 4idely, even in neighboring countries, apparently because of differences in health care systems"2!3.he World 9ealth 1rgani?ation declared ./ a global health emergency in ##+, and the =top ./ @artnership developed a Alobal @lan to =top .uberculosis that aims to save ( million lives bet4een *$$& and *$!"2&3Contents2hide3 1ther names *=ymptoms +/acterial species o +"Bvolution (.ransmission !@athogenesis & of active cases, the infection moves from the lungs, causing other kinds of ./ more common in immunosuppressed persons and young children" B6trapulmonary infection sites include the pleura, the central nervous system in meningitis, the lymphatic system in scrofula of the neck, the genitourinary system in urogenital tuberculosis, and bones and 0oints in @ott5s disease of the spine" An especially serious form is disseminated ./, more commonly kno4n as miliary tuberculosis" Although e6trapulmonary ./ is not contagious, it may co-e6ist 4ith pulmonary ./, 4hich is contagious"2$3Bacterial speciesMain article Mycobacterium tuberculosis=canning electron micrograph of Mycobacterium tuberculosis.he primary cause of ./ , Mycobacterium tuberculosis ,E" ./-, is an aerobic bacterium that divides every & to *$ hours, an e6tremely slo4 rate compared 4ith other bacteria, 4hich usually divide in less than an hour"23 ,For e6ample, one of the fastest-gro4ing bacteria is a strain of ". coli that can divide roughly every *$ minutes"- =ince E./ has a cell 4all but lacks a phospholipid outer membrane, it is classified as a Aram-positive bacterium" 9o4ever, if a Aram stain is performed, E./ either stains very 4eakly Aram-positive or does not retain dye due to the high lipid F mycolic acid content of its cell 4all"2*3 E./ is a small rod-like bacillus that can 4ithstand 4eak disinfectants and survive in a dry state for 4eeks" :n nature, the bacterium can gro4 only 4ithin the cells ofa host organism, but M. tuberculosis can be cultured in vitro"2+3Gsing certain histological techniHues on e6pectorate samples from phlegm ,also called sputum-, scientists can identify E./ under a regular microscope" =ince E./ retains certain stains after being treated 4ith acidic solution, it is classified as an acid-fast bacillus ,AF/-"2*3 .he most common staining techniHue, the Iiehl-7eelsen stain, dyes AF/s a bright red that stands out clearly against a blue background" 1ther 4ays to visuali?e AF/s include an auramine-rhodamine stain and fluorescent microscopy".he M. tuberculosis comple6 includes + other ./-causing mycobacteria: M. bovis, M. africanum and M. microti" .he first t4o only very rarely cause disease in immunocompetent people" 1n the other hand, although M. microti is not usually pathogenic, it is possible that the prevalence of M. microti infections has been underestimated"2(31ther kno4n pathogenic mycobacteria include Mycobacterium le#rae, Mycobacterium avium and M. $ansasii" .he last t4o are part of the nontuberculous mycobacteria ,7.E- group" 7ontuberculous mycobacteria cause neither ./ nor leprosy, but they %o cause pulmonary diseases resembling ./"2!3'!olution infection rate" A person 4ith active but untreated tuberculosis can infect $D! other people per year"2*3 1thers at risk include people in areas 4here ./ is common, people 4ho in0ect illicit drugs ,especially 4hen sharing needles-, residents and employees of high-risk congregate settings, medically under-served and lo4-income populations, high-risk racial or ethnic minority populations, children e6posed to adults in high-risk categories, patients immunocompromised by conditions such as 9:;)A: of those infected 4ith Mycobacterium tuberculosis have asymptomatic, latent./ infection ,sometimes called L./:-, 4ith only a $> lifetime chance that a latent infection 4ill progress to ./ disease" 9o4ever, if untreated, the death rate for these active ./ cases is more than !$>"2*3./ infection begins 4hen the mycobacteria reach the pulmonary alveoli, 4here they invade and replicate 4ithin alveolar macrophages"2**3 .he primary site of infection in the lungs is called the Ahon focus" /acteria are picked up by dendritic cells, 4hich do not allo4 replication, although these cells can transport the bacilli to local ,mediastinal- lymph nodes" Further spread is through the bloodstream to the more distant tissues and organs 4here secondary ./ lesions can develop in lung apices, peripheral lymph nodes, kidneys, brain, and bone"2*+3 All parts of the body can be affected by the disease, though it rarely affects the heart, skeletal muscles, pancreas and thyroid"2*(3.uberculosis is classified as one of the granulomatous inflammatory conditions" Eacrophages, . lymphocytes, / lymphocytes and fibroblasts are among the cells that aggregate to form a granuloma, 4ith lymphocytes surrounding the infected macrophages".he granuloma functions not only to prevent dissemination of the mycobacteria, but also provides a local environment for communication of cells of the immune system" Within the granuloma, . lymphocytes ,C