لاعضاءالمنتدى فقط الحصيلةTB

من طرف محمد حبيب الخميس أكتوبر 29, 2009 9:30 pm

Tuberculosis (abbreviated TB, which can also stand for tubercle bacillus) is a common and often deadly infectious disease caused by mycobacterium. In humans, Mycobacterium tuberculosis is the primary causative bacterium although other mycobacteria such as Mycobacterium bovis, Mycobacterium africanum, Mycobacterium Canetti, and Mycobacterium microti are also causes.^[1] Tuberculosis usually attacks the lungs (as pulmonary TB) but can also affect the central nervous system, the lymphatic system, the circulatory system, the genitourinary system, the gastrointestinal system, bones, joints, and even the skin.
Tuberculosis is spread through the air, when people who have the disease cough, sneeze, or spit. Most infections in human beings will result in asymptomatic, latent infection, and about one in ten latent infections will eventually progress to active disease, which, if left untreated, kills more than half of its victims. The classic symptoms of tuberculosis are a chronic cough with blood-tinged sputum, fever, night sweats, and weight loss. Infection of other organs causes a wide range of symptoms.
The diagnosis relies on radiology (commonly chest X-rays), a tuberculin skin test, blood tests, as well as microscopic examination and microbiological culture of bodily fluids. Tuberculosis treatment is difficult and requires long courses of multiple antibiotics. Contacts are also screened and treated if necessary. Antibiotic resistance is a growing problem in (extensively) multi-drug-resistant tuberculosis. Prevention relies on screening programs and vaccination, usually with Bacillus Calmette-Guérin (BCG vaccine).
One–third of the world's current population has been infected with M. tuberculosis. New infections occur at a rate of one per second.^[2] The proportion of people in the general population who become sick with tuberculosis each year is stable or falling worldwide but, because of population growth, the absolute number of new cases is still increasing.^[3]
In 2004, mortality and morbidity statistics included 14.6 million chronic active cases, 8.9 million new cases, and 1.6 million deaths, mostly in developing countries.^[2] In addition, a rising number of people in the developed world are contracting tuberculosis because their immune systems are compromised by immunosuppressive drugs, substance abuse, or AIDS. The distribution of tuberculosis is not uniform across the globe; about 80% of the population in many Asian and African countries test positive in tuberculin tests, while only 5-10% of the US population test positive.^[1] It is estimated that the US has 25,000 new cases of tuberculosis each year, 40% of which occur in immigrants from countries

Classification System for TB ClassTypeDescription
0	No TB exposure Not infected	No history of exposure Negative reaction to tuberculin skin test
1	TB exposure No evidence of infection	History of exposure Negative reaction to tuberculin skin test
2	TB infection No disease	Positive reaction to tuberculin skin test Negative bacteriologic studies (if done) No clinical, bacteriologic, or radiographic evidence of TB
3	TB, clinically active	M. tuberculosis cultured (if done) Clinical, bacteriologic, or radiographic evidence of current disease
4	TB Not clinically active	History of episode(s) of TB or Abnormal but stable radiographic findings Positive reaction to the tuberculin skin test Negative bacteriologic studies (if done) and No clinical or radiographic evidence of current disease
5	TB suspect	Diagnosis pending TB disease should be ruled in or out within 3 months

Main symptoms of variants and stages of tuberculosis,^[4][5] with many symptoms overlapping with other variants, while others are more (but not entirely) specific for certain variants. Multiple variants may be present simultaneously.

When the disease becomes active, 75% of the cases are pulmonary TB. Symptoms include chest pain, coughing up blood, and a productive, prolonged cough for more than three weeks. Systemic symptoms include fever, night sweats, appetite loss, weight loss, pallor, and often a tendency to very easily.^[2]
In the other 25% of active cases, the infection moves from the lungs, causing other kinds of TB, collectively denoted extra pulmonary tuberculosis.^[6] This occurs more commonly in immunosuppressed persons and young children. Extrapulmonary infection sites include the pleura in tuberculosis pleurisy, the central nervous system in meningitis, the lymphatic system in scrofula of the neck, the genitourinary system in urogenital tuberculosis, and bones and joints in Pott's disease of the spine. An especially serious form is disseminated TB, more commonly known as military tuberculosis. Extrapulmonary TB may co-exist with pulmonary TB as well.^[7]
Causes

: Mycobacterium tuberculosis

Scanning electron micrograph of Mycobacterium tuberculosis

The primary cause of TB, Mycobacterium tuberculosis, is an aerobic bacterium that divides every 16 to 20 hours, an extremely slow rate compared with other bacteria, which usually divide in less than an hour.^[8] (For example, one of the fastest-growing bacteria is a strain of E. coli that can divide roughly every 20 minutes.) Since MTB has a cell wall but lacks a phospholipid outer membrane, it is classified as a Gram-positive bacterium. However, if a Gram stain is performed, MTB either stains very weakly Gram-positive or does not retain dye due to the high lipid & mycolic acid content of its cell wall.^[9] MTB is a small rod-like bacillus that can withstand weak disinfectants and survive in a dry state for weeks. In nature, the bacterium can grow only within the cells of a organism, but M. tuberculosis can be cultured in vitro
Using histological stains on expectorate samples from phlegm (also called sputum), scientists can identify MTB under a regular microscope. Since MTB retains certain stains after being treated with acidic solution, it is classified as an acid-fast bacillus (AFB).^[1][9] The most common acid-fast staining technique, the Ziehl-Neelsen stain, dyes AFBs a bright red that stands out clearly against a blue background. Other ways to visualize AFBs include an auramine-rhodamine stain and fluorescent microscopy.
Phylogenetic tree of the genus Mycobacterium.

The M. tuberculosis complex includes three other TB-causing mycobacteria: M. bovis, M. africanum, and M. microti. M. africanum is not widespread, but in parts of Africa it is a significant cause of tuberculosis.^[11][12] M. bovis was once a common cause of tuberculosis, but the introduction of pasteurized milk has largely eliminated this as a public health problem in developed countries.^[1][13] M. microti is mostly seen in immunodeficient people, although it is possible that the prevalence of this pathogen has been underestimated.^[14]
Other known pathogenic mycobacterium include Mycobacterium leprae, Mycobacterium avium and M. kansasii. The last two are part of the nontuberculous mycobacteria (NTM) group. Nontuberculous mycobacteria cause neither TB nor leprosy, but they do cause pulmonary diseases resembling TB.
Risk factors

Persons with silicosis have an approximately 30-fold greater risk for developing TB. Persons with chronic renal failure who are on hemodialysis also have an increased risk: 10—25 times greater than the general population. Persons with diabetes mellitus have a risk for developing active TB that is two to four times greater than persons without diabetes mellitus, and this risk is likely greater in persons with insulin-dependent or poorly controlled diabetes. Other clinical conditions that have been associated with active TB include gastrectomy with attendant weight loss and malabsorption, jejunoileal bypass, renal and cardiac transplantation, carcinoma of the head or neck, and other neoplasms (e.g., lung cancer, lymphoma, and leukemia) [1].
Given that silicosis greatly increases the risk of tuberculosis, more research about the effect of various (indoor) air pollutants on the disease would be necessary. Some possible indoor source of silica includes paint, concrete and Portland cement.
Low body weight is associated with risk of tuberculosis as well. A body mass index (BMI) below 18.5 increases the risk by 2—3 times. On the other hand, an increase in body weight lowers the risk [2], [3]. Patients with diabetes mellitus are at increased risk of contracting tuberculosis,^[16] and they have a poorer response to treatment, possibly due to poorer drug absorption^[17]
Other conditions that increase risk include IV drug abuse; recent TB infection or a history of inadequately treated TB; chest X-ray suggestive of previous TB, showing fibrotic lesions and nodules; prolonged corticosteroid therapy and other immunosuppressive therapy;Immunocompromised patients (30-40% of AIDS patients in the world also have TB) hematologic and reticuloendothelial diseases, such as leukemia and Hodgkin's disease; end-stage kidney disease; intestinal bypass; chronic malabsorption syndromes; vitamin D deficiency;^[18] and low body weight.^[1][7]
Twin studies in the 1940s showed that susceptibility to TB was heritable. If one of a pair of twins got TB, then and the other was more likely to get TB if he was identical than if he was not.^[19] Since then, specific gene polymorphisms in IL12B have been linked to tuberculosis susceptibility.^[20]
Some drugs, including rheumatoid arthritis drugs that work by blocking tumor necrosis factor-alpha (an inflammation-causing cytokine), raise the risk of activating a latent infection due to the importance of this cytokine in the immune defense against TB.^[21]
TB prevention and control takes two parallel approaches. In the first, people with TB and their contacts are identified and then treated. Identification of infections often involves testing high-risk groups for TB. In the second approach, children are vaccinated to protect them from TB. No vaccine is available that provides reliable protection for adults. However, in tropical areas where the levels of other species of mycobacterium are high, exposure to nontuberculous mycobacterium gives some protection against TB.^[38]
The World Health Organization (W.H.O.) declared TB a global health emergency in 1993, and the Stop TB Partnership developed a Global Plan to Stop Tuberculosis that aims to save 14 million lives between 2006 and 2015.^[39] Since humans are the only host of Mycobacterium tuberculosis, eradication would be possible: a goal that would be helped greatly by an effective vaccine.^[40]

من طرف elnagar الخميس أكتوبر 29, 2009 10:58 pm

مفيش حصيلة للدفعة الاولى

من طرف محمد حبيب السبت أكتوبر 31, 2009 7:16 pm

انت تؤمر يا نجار
اللى انت عايزوا هتلاقيه

**snow white** .... تاريخ التسجيل : 12/10/2009

لا بجد كده بداية صح جدا ,اشكرك

من طرف sinderlla السبت نوفمبر 14, 2009 11:48 am

شكرا يا محمد بس فينpathphsyology

من طرف محمد حبيب الثلاثاء نوفمبر 17, 2009 8:14 pm

اوكى يا سندريلا
بعد كدة

لاعضاءالمنتدى فقط الحصيلةTB

لاعضاءالمنتدى فقط الحصيلةTB

رد: لاعضاءالمنتدى فقط الحصيلةTB

رد: لاعضاءالمنتدى فقط الحصيلةTB

رد: لاعضاءالمنتدى فقط الحصيلةTB

رد: لاعضاءالمنتدى فقط الحصيلةTB

رد: لاعضاءالمنتدى فقط الحصيلةTB