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Tuberculosis(kifua kikuu)

Discussion in 'JF Doctor' started by KAKA A TAIFA, Jun 30, 2011.


    KAKA A TAIFA JF-Expert Member

    Jun 30, 2011
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    Tuberculosis, MTB or TB (short for tubercle bacillus) is a common and in many cases lethal infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis.[SUP][1][/SUP] Tuberculosis usually attacks the lungs but can also affect other parts of the body. It is spread through the air when people who have an active MTB infection cough, sneeze, or otherwise transmit their saliva through the air.[SUP][2][/SUP] Most infections in humans result in an asymptomatic, latent infection, and about one in ten latent infections eventually progresses to active disease, which, if left untreated, kills more than 50% of its victims.
    The classic symptoms are a chronic cough with blood-tinged sputum, fever, night sweats, and weight loss (the last giving rise to the formerly prevalent colloquial term "consumption"). Infection of other organs causes a wide range of symptoms. 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. Treatment is difficult and requires long courses of multiple antibiotics. Social 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 vaccine.
    One third of the world's population is thought to be infected with M. tuberculosis,[SUP][3][/SUP][SUP][4][/SUP] and new infections occur at a rate of about one per second.[SUP][3][/SUP] The proportion of people 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.[SUP][3][/SUP] In 2007 there were an estimated 13.7 million chronic active cases, 9.3 million new cases, and 1.8 million deaths, mostly in developing countries.[SUP][5][/SUP] In addition, more people in the developed world contract tuberculosis because their immune systems are more likely to be compromised due to higher exposure to 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.[SUP][[/SUP]Signs and symptoms
    [SUP]Main symptoms of variants and stages of tuberculosis,[/SUP][SUP][6][/SUP][SUP] with many symptoms overlapping with other variants, while others are more (but not entirely) specific for certain variants. Multiple variants may be present simultaneously.[/SUP]

    [SUP]Scanning electron micrograph of Mycobacterium tuberculosis[/SUP]

    [SUP]Phylogenetic tree[/SUP][SUP] of the genus Mycobacterium.[/SUP]

    [SUP]When the disease becomes active, 75% of the cases involve infection in the lungs ([/SUP][SUP]pulmonary[/SUP][SUP] TB). Symptoms include [/SUP][SUP]chest pain[/SUP][SUP], [/SUP][SUP]coughing up blood[/SUP][SUP], and a productive, prolonged cough for more than three weeks. Systemic symptoms include [/SUP][SUP]fever[/SUP][SUP], [/SUP][SUP]chills[/SUP][SUP], [/SUP][SUP]night sweats[/SUP][SUP], [/SUP][SUP]appetite loss[/SUP][SUP], [/SUP][SUP]weight loss[/SUP][SUP], [/SUP][SUP]pallor[/SUP][SUP], and [/SUP][SUP]fatigue[/SUP][SUP].[/SUP][SUP][7][/SUP]
    [SUP]In the other 25% of active cases, the infection moves from the lungs, causing other kinds of TB, collectively denoted extrapulmonary tuberculosis.[/SUP][SUP][8][/SUP][SUP] This occurs more commonly in [/SUP][SUP]immunosuppressed[/SUP][SUP] persons and young children. Extrapulmonary infection sites include the [/SUP][SUP]pleura[/SUP][SUP] in tuberculous pleurisy, the [/SUP][SUP]central nervous system[/SUP][SUP] in [/SUP][SUP]meningitis[/SUP][SUP], the [/SUP][SUP]lymphatic system[/SUP][SUP] in [/SUP][SUP]scrofula[/SUP][SUP] of the neck, the [/SUP][SUP]genitourinary system[/SUP][SUP] in [/SUP][SUP]urogenital tuberculosis[/SUP][SUP], and bones and joints in [/SUP][SUP]Pott's disease[/SUP][SUP] of the spine. An especially serious form is disseminated TB, more commonly known as [/SUP][SUP]miliary tuberculosis[/SUP][SUP]. Extrapulmonary TB may co-exist with pulmonary TB.[/SUP][SUP][9][/SUP]Causes
    Main article: Mycobacterium tuberculosis
    The main cause of TB, Mycobacterium tuberculosis (MTB), is a small aerobic non-motile bacillus. High lipid content of this pathogen accounts for many of its unique clinical characteristics.[SUP][10][/SUP] It divides every 16 to 20 hours, an extremely slow rate compared with other bacteria, which usually divide in less than an hour.[SUP][11][/SUP] 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 as a result of the high lipid & mycolic acid content of its cell wall.[SUP][12][/SUP] MTB can withstand weak disinfectants and survive in a dry state for weeks. In nature, the bacterium can grow only within the cells of a host organism, but M. tuberculosis can be cultured in vitro.[SUP][13][/SUP]
    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).[SUP][1][/SUP][SUP][12][/SUP] 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.
    The M. tuberculosis complex includes four other TB-causing mycobacteria: M. bovis, M. africanum, M. canetti and M. microti.[SUP][14][/SUP] M. africanum is not widespread, but in parts of Africa it is a significant cause of tuberculosis.[SUP][15][/SUP][SUP][16][/SUP] 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.[SUP][1][/SUP][SUP][17][/SUP] M. canetti is rare and seems to be limited to Africa, although a few cases have been seen in African emigrants.[SUP][18][/SUP] M. microti is mostly seen in immunodeficient people, although it is possible that the prevalence of this pathogen has been underestimated.[SUP][19][/SUP]
    Other known pathogenic mycobacteria include Mycobacterium leprae, Mycobacterium avium and M. kansasii. The latter two are part of the nontuberculous mycobacteria (NTM) group. Nontuberculous mycobacteria cause neither TB nor leprosy, but they do cause pulmonary diseases resembling TB.[SUP][20][/SUP]Risk factors
    [SUP]People with [/SUP][SUP]silicosis[/SUP][SUP] have an approximately 30-fold greater risk for developing TB.[/SUP][SUP][21][/SUP][SUP] Silica particles irritate the respiratory system, causing immunogenic responses such as [/SUP][SUP]phagocytosis[/SUP][SUP], which, as a consequence, results in high lymphatic vessel deposits.[/SUP][SUP][22][/SUP][SUP] It is this interference and blockage of [/SUP][SUP]macrophage[/SUP][SUP] function that increases the risk of tuberculosis.[/SUP][SUP][23][/SUP][SUP] Persons with chronic renal failure and also on hemodialysis have an increased risk.[/SUP][SUP][24][/SUP][SUP] Persons with [/SUP][SUP]diabetes mellitus[/SUP][SUP] have a risk for developing active TB that is two to four times greater than persons without diabetes mellitus, and this risk is likely to be greater in persons with insulin-dependent or poorly controlled diabetes.[/SUP][SUP][25][/SUP][SUP] Other clinical conditions that have been associated with active TB include [/SUP][SUP]gastrectomy[/SUP][SUP] 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).[/SUP][SUP][26][/SUP]
    [SUP]Given that silicosis greatly increases the risk of tuberculosis, more research about the effect of various indoor or outdoor air pollutants on the disease would be necessary. Some possible indoor sources of silica include paint, [/SUP][SUP]concrete[/SUP][SUP] and [/SUP][SUP]Portland cement[/SUP][SUP]. Crystalline silica is found in concrete, masonry, sandstone, rock, paint, and other abrasives. The cutting, breaking, crushing, drilling, grinding, or abrasive blasting of these materials may produce fine silica dust. It can also be in soil, mortar, plaster, and shingles.[/SUP][SUP][27][/SUP]
    [SUP]Low body weight is associated with risk of tuberculosis as well. A [/SUP][SUP]body mass index[/SUP][SUP] (BMI) below 18.5 increases the risk by 2–3 times. An increase in body weight lowers the risk.[/SUP][SUP][28][29][/SUP][SUP] People with [/SUP][SUP]diabetes mellitus[/SUP][SUP] are at increased risk of contracting tuberculosis,[/SUP][SUP][30][/SUP][SUP] and they have a poorer response to treatment, possibly due to poorer drug absorption.[/SUP][SUP][31][/SUP]
    [SUP]The correlation between diabetes mellitus and TB is concerning for public health because it shows a distinct connection between a contagious disease and a chronic disease. TB is a highly contagious air-born bacteria, therefore contracting tuberculosis depends on whether the person comes into contact with the bacteria or not. Diabetics do not have an increased risk of contracting latent tuberculosis but studies have shown that people with diabetes mellitus are more likely to move from a latent form of TB to an active form of TB. This is where the public concern comes from, because when TB is active it is contagious and potentially fatal.[/SUP][SUP][32][/SUP]
    [SUP]Other conditions that increase risk include the sharing of needles among [/SUP][SUP]IV drug users[/SUP][SUP]; recent TB infection or a history of inadequately treated TB; chest X-ray suggestive of previous TB, showing fibrotic lesions and nodules; prolonged [/SUP][SUP]corticosteroid[/SUP][SUP] therapy and other immunosuppressive therapy; Immunocompromised people (30–40% of people with AIDS in the world also have TB) [/SUP][SUP]hematologic[/SUP][SUP] and [/SUP][SUP]reticuloendothelial[/SUP][SUP] diseases, such as [/SUP][SUP]leukemia[/SUP][SUP] and [/SUP][SUP]Hodgkin's disease[/SUP][SUP]; [/SUP][SUP]end-stage kidney disease[/SUP][SUP]; intestinal bypass; chronic [/SUP][SUP]malabsorption[/SUP][SUP] syndromes; vitamin D deficiency;[/SUP][SUP][33][/SUP][SUP] and low body weight.[/SUP][SUP][1][9][/SUP]
    [SUP]Twin studies[/SUP][SUP] in the 1940s showed that susceptibility to TB was heritable. If one of a pair of twins got TB, then the other was more likely to get TB if he was identical than if he was not.[/SUP][SUP][34][/SUP][SUP] These findings were more recently confirmed by a series of studies in [/SUP][SUP]South Africa[/SUP][SUP].[/SUP][SUP][35][36][37][/SUP][SUP] Specific gene polymorphisms in IL12B have been linked to tuberculosis susceptibility.[/SUP][SUP][38][/SUP]
    [SUP]Some drugs, including [/SUP][SUP]rheumatoid arthritis[/SUP][SUP] drugs that work by blocking [/SUP][SUP]tumor necrosis factor-alpha[/SUP][SUP] (an inflammation-causing [/SUP][SUP]cytokine[/SUP][SUP]), raise the risk of activating a latent infection due to the importance of this cytokine in the immune defense against TB[/SUP]Mechanism[SUP]Transmission[/SUP]
    [SUP]When people suffering from active pulmonary TB cough, sneeze, speak, sing, or spit, they expel infectious [/SUP][SUP]aerosol[/SUP][SUP] droplets 0.5 to 5 [/SUP][SUP]µm[/SUP][SUP] in diameter. A single sneeze can release up to 40,000 droplets.[/SUP][SUP][40][/SUP][SUP] Each one of these droplets may transmit the disease, since the infectious dose of tuberculosis is very low and inhaling fewer than ten bacteria may cause an infection.[/SUP][SUP][41][42][/SUP]
    [SUP]People with prolonged, frequent, or intense contact are at particularly high risk of becoming infected, with an estimated 22% infection rate. A person with active but untreated tuberculosis can infect 10–15 other people per year.[/SUP][SUP][3][/SUP][SUP] Others at risk include people in areas where TB is common, people who inject illicit drugs, residents and employees of high-risk congregate settings, medically under-served and low-income populations, high-risk racial or ethnic minority populations, children exposed to adults in high-risk categories, those who are [/SUP][SUP]immunocompromised[/SUP][SUP] by conditions such as [/SUP][SUP]HIV[/SUP][SUP]/[/SUP][SUP]AIDS[/SUP][SUP], people who take immunosuppressant drugs, and health care workers serving these high-risk clients.[/SUP][SUP][43][/SUP]
    [SUP]Transmission can only occur from people with active—not latent—TB.[/SUP][SUP][1][/SUP][SUP] The probability of transmission from one person to another depends upon the number of infectious droplets expelled by a carrier, the effectiveness of ventilation, the duration of exposure, and the [/SUP][SUP]virulence[/SUP][SUP] of the M. tuberculosis [/SUP][SUP]strain[/SUP][SUP].[/SUP][SUP][9][/SUP][SUP] The chain of transmission can be broken by isolating people with active disease and starting effective anti-tuberculous therapy. After two weeks of such treatment, people with [/SUP][SUP]non-resistant[/SUP][SUP] active TB generally cease to be contagious. If someone does become infected, then it will take three to four weeks before the newly infected person can transmit the disease to others.[/SUP][SUP][44][/SUP][SUP]][/SUP][SUP] Pathogenesis[/SUP]
    [SUP]About 90% of those infected with Mycobacterium tuberculosis have [/SUP][SUP]asymptomatic[/SUP][SUP], latent TB infection (sometimes called LTBI), with only a 10% lifetime chance that a latent infection will progress to TB disease.[/SUP][SUP][1][/SUP][SUP] However, if untreated, the death rate for these active TB cases is more than 50%.[/SUP][SUP][3][/SUP]
    [SUP]TB infection begins when the mycobacteria reach the [/SUP][SUP]pulmonary alveoli[/SUP][SUP], where they invade and replicate within the [/SUP][SUP]endosomes[/SUP][SUP] of alveolar [/SUP][SUP]macrophages[/SUP][SUP].[/SUP][SUP][1][45][/SUP][SUP] The primary site of infection in the lungs is called the [/SUP][SUP]Ghon focus[/SUP][SUP], and is generally located in either the upper part of the lower lobe, or the lower part of the [/SUP][SUP]upper lobe[/SUP][SUP].[/SUP][SUP][1][/SUP][SUP] Bacteria are picked up by [/SUP][SUP]dendritic cells[/SUP][SUP], which do not allow replication, although these cells can transport the bacilli to local ([/SUP][SUP]mediastinal[/SUP][SUP]) [/SUP][SUP]lymph nodes[/SUP][SUP]. Further spread is through the bloodstream to other tissues and organs where secondary TB lesions can develop in other parts of the lung (particularly the apex of the upper lobes), peripheral lymph nodes, kidneys, brain, and bone.[/SUP][SUP][1][46][/SUP][SUP] All parts of the body can be affected by the disease, though it rarely affects the [/SUP][SUP]heart[/SUP][SUP], [/SUP][SUP]skeletal muscles[/SUP][SUP], [/SUP][SUP]pancreas[/SUP][SUP] and [/SUP][SUP]thyroid[/SUP][SUP].[/SUP][SUP][47][/SUP]
    [SUP]Tuberculosis is classified as one of the [/SUP][SUP]granulomatous[/SUP][SUP] inflammatory conditions. [/SUP][SUP]Macrophages[/SUP][SUP], [/SUP][SUP]T lymphocytes[/SUP][SUP], [/SUP][SUP]B lymphocytes[/SUP][SUP] and [/SUP][SUP]fibroblasts[/SUP][SUP] are among the cells that aggregate to form [/SUP][SUP]granulomas[/SUP][SUP], with [/SUP][SUP]lymphocytes[/SUP][SUP] surrounding the infected macrophages. The granuloma prevents dissemination of the mycobacteria and provides a local environment for interaction of cells of the immune system. Bacteria inside the granuloma can become dormant, resulting in a latent infection. Another feature of the granulomas of human tuberculosis is the development of abnormal cell death ([/SUP][SUP]necrosis[/SUP][SUP]) in the center of [/SUP][SUP]tubercles[/SUP][SUP]. To the naked eye this has the texture of soft white cheese and is termed [/SUP][SUP]caseous[/SUP][SUP]necrosis[/SUP][SUP].[/SUP][SUP][48][/SUP]
    [SUP]If TB bacteria gain entry to the bloodstream from an area of damaged tissue they spread through the body and set up many foci of infection, all appearing as tiny white tubercles in the tissues. This severe form of TB disease is most common in infants and the elderly and is called [/SUP][SUP]miliary tuberculosis[/SUP][SUP]. People with this disseminated TB have a fatality rate near 100% if untreated. However, If treated early, the fatality rate is reduced to about 10%.[/SUP][SUP][49][/SUP]
    [SUP]In many people the infection waxes and wanes. Tissue destruction and necrosis are balanced by healing and [/SUP][SUP]fibrosis[/SUP][SUP].[/SUP][SUP][48][/SUP][SUP] Affected tissue is replaced by scarring and cavities filled with cheese-like white necrotic material. During active disease, some of these cavities are joined to the air passages [/SUP][SUP]bronchi[/SUP][SUP] and this material can be coughed up. It contains living bacteria and can therefore pass on infection. Treatment with appropriate [/SUP][SUP]antibiotics[/SUP][SUP] kills bacteria and allows healing to take place. Upon cure, affected areas are eventually replaced by scar tissue.[/SUP][SUP][48][/SUP]
    [SUP]If untreated, infection with Mycobacterium tuberculosis can cause [/SUP][SUP]lobar pneumonia[/SUP][SUP].[/SUP][SUP][50][/SUP]
    [h=2][SUP] Diagnosis[/SUP][/h][SUP]Main article: [/SUP][SUP]Tuberculosis diagnosis[/SUP]
    [SUP]See also: [/SUP][SUP]Tuberculosis classification[/SUP]
    [SUP]Mycobacterium tuberculosis[/SUP][SUP] (stained red) in sputum[/SUP]

    [SUP]Tuberculosis is diagnosed definitively by identifying the causative organism (Mycobacterium tuberculosis) in a clinical sample (for example, [/SUP][SUP]sputum[/SUP][SUP] or [/SUP][SUP]pus[/SUP][SUP]). When this is not possible, a probable – although sometimes inconclusive[/SUP][SUP][2][/SUP][SUP] – diagnosis may be made using imaging (X-rays or scans), a [/SUP][SUP]tuberculin skin test (Mantoux test)[2][/SUP][SUP] and/or a Interferon Gamma Release Assay (IGRA).[/SUP]
    [SUP]The main problem with tuberculosis diagnosis is the difficulty in culturing this slow-growing organism in the laboratory (it may take 4 to 12 weeks for blood or sputum culture). A complete medical evaluation for TB must include a medical history, a physical examination, a [/SUP][SUP]chest X-ray[/SUP][SUP], microbiological smears, and cultures. It may also include a [/SUP][SUP]tuberculin skin test[/SUP][SUP], a [/SUP][SUP]serological[/SUP][SUP] test. The interpretation of the tuberculin skin test depends upon the person's risk factors for infection and progression to TB disease, such as exposure to other cases of TB or immunosuppression.[/SUP][SUP][9][/SUP]
    [SUP]Currently, latent infection is diagnosed in a non-immunized person by a tuberculin skin test, which yields a delayed hypersensitivity type response to [/SUP][SUP]an extract[/SUP][SUP] made from M. tuberculosis.[/SUP][SUP][1][/SUP][SUP] Those immunized for TB or with past-cleared infection will respond with delayed hypersensitivity parallel to those currently in a state of infection, so the test must be used with caution, particularly with regard to persons from countries where TB immunization is common.[/SUP][SUP][51][/SUP][SUP] Tuberculin tests have the disadvantage of producing false negatives, especially when the person is [/SUP][SUP]co-morbid[/SUP][SUP] with [/SUP][SUP]sarcoidosis[/SUP][SUP], Hodgkins lymphoma, malnutrition, or most notably active tuberculosis disease.[/SUP][SUP][1][/SUP][SUP] The newer interferon release assays (IGRAs) such as [/SUP][SUP]T-SPOT.TB[/SUP][SUP] and [/SUP][SUP]QuantiFERON[/SUP][SUP]-TB Gold In Tube overcome many of these problems. IGRAs are in vitro blood tests that are more specific than the skin test. IGRAs detect the release of [/SUP][SUP]interferon gamma[/SUP][SUP] in response to mycobacterial proteins such as [/SUP][SUP]ESAT-6[/SUP][SUP].[/SUP][SUP][52][/SUP][SUP] These are not affected by immunization or [/SUP][SUP]environmental mycobacteria[/SUP][SUP], so generate fewer [/SUP][SUP]false positive[/SUP][SUP] results.[/SUP][SUP][53][/SUP][SUP] There is also evidence that IGRAs are more sensitive than the skin test.[/SUP][SUP][54][/SUP]Treatment
    Main article: Tuberculosis treatment
    Treatment for TB uses antibiotics to kill the bacteria. Effective TB treatment is difficult, due to the unusual structure and chemical composition of the mycobacterial cell wall, which makes many antibiotics ineffective and hinders the entry of drugs.[SUP][84][/SUP][SUP][85][/SUP][SUP][86][/SUP][SUP][87][/SUP] The two antibiotics most commonly used are isoniazid and rifampicin. However, instead of the short course of antibiotics typically used to cure other bacterial infections, TB requires much longer periods of treatment (around 6 to 24 months) to entirely eliminate mycobacteria from the body.[SUP][9][/SUP] Latent TB treatment usually uses a single antibiotic, while active TB disease is best treated with combinations of several antibiotics, to reduce the risk of the bacteria developing antibiotic resistance.[SUP][88][/SUP] People with latent infections are treated to prevent them from progressing to active TB disease later in life.
    Drug-resistant tuberculosis is transmitted in the same way as regular TB. Primary resistance occurs in persons infected with a resistant strain of TB. A person with fully susceptible TB develops secondary resistance (acquired resistance) during TB therapy because of inadequate treatment, not taking the prescribed regimen appropriately, or using low-quality medication.[SUP][88][/SUP] Drug-resistant TB is a public health issue in many developing countries, as treatment is longer and requires more expensive drugs. Multi-drug-resistant tuberculosis (MDR-TB) is defined as resistance to the two most effective first-line TB drugs: rifampicin and isoniazid. Extensively drug-resistant TB (XDR-TB) is also resistant to three or more of the six classes of second-line drugs.[SUP][89][/SUP]
    The DOTS (Directly Observed Treatment Short-course) strategy of tuberculosis treatment recommended by WHO was based on clinical trials done in the 1970s by Tuberculosis Research Centre, Chennai, India. The country in which a person with TB lives can determine what treatment they receive. This is because multidrug-resistant tuberculosis is resistant to most first-line medications, the use of second-line antituberculosis medications is necessary to cure the person. However, the price of these medications is high; thus poor people in the developing world have no or limited access to these treatments.[SUP][90][/SUP]
  2. Masanilo

    Masanilo JF-Expert Member

    Jun 30, 2011
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    Next time weka Link ulipocopy, kupunguza nafasi na pia jenga tabia ya kuacknowledge kazi za wengine. Hii ni kama Plagiarism of the first order. Pamoja ya kuwa ni ujumbe mzuri.
  3. njiwa

    njiwa JF-Expert Member

    Jul 2, 2011
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    exactly mkuu .... jamaa ana copy & paste info ambazo hata yeye hakuzisoma