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Causes

Mycobacteria

Main article:Mycobacterium tuberculosis

Scanning electron micrographofMycobacterium tuberculosis

The main cause of TB isMycobacterium tuberculosis,a small,aerobic,nonmotilebacillus.[9]

The

highlipidcontent of this pathogen accounts for many of its unique clinical

characteristics.[18]

Itdividesevery 16 to 20 hours, which is an extremely slow rate compared with other

bacteria, which usually divide in less than an hour.[19]

Mycobacteria have anouter membranelipid

bilayer.[20]

If aGram stainis performed, MTB either stains very weakly "Gram-positive" or does not retain

dye as a result of the highlipidandmycolic acidcontent of its cell wall.[21]

MTB can withstand

weakdisinfectantsand survive in adry statefor weeks. In nature, the bacterium can grow only within thecells of ahostorganism, but M. tuberculosiscan be culturedin the laboratory.

[22]

Usinghistologicalstains onexpectoratedsamples fromphlegm(also called "sputum"), scientists can

identify MTB under a regular (light) microscope. Since MTB retains certain stains even after being treated

with acidic solution, it is classified as anacid-fast bacillus(AFB).[1][21]

The most common acid-fast staining

techniques are theZiehlNeelsen stain,which dyes AFBs a bright red that stands out clearly against a

blue background,[23]

and theauramine-rhodamine stainfollowed byfluorescence microscopy.[24]

The M. tuberculosiscomplex (MTBC) includes four other TB-causingmycobacteria:M. bovis,M.

africanum,M. canetti,andM. microti.[25]

M. africanumis not widespread, but it is a significant cause of

tuberculosis in parts of Africa.[26][27]

M. boviswas once a common cause of tuberculosis, but the

introduction ofpasteurized milkhas largely eliminated this as a public health problem in developed

countries.[1][28]

M. canettiis rare and seems to be limited to the Horn of Africa,although a few cases have

been seen in African emigrants.[29][30]

M. microtiis also rare and is mostly seen in immunodeficient people,

although theprevalenceof this pathogen has possibly been significantly underestimated.[31]

Other known pathogenic mycobacteria includeM. leprae,M. avium,andM. kansasii.The latter two

species are classified as "nontuberculous mycobacteria"(NTM). NTM cause neither TB norleprosy,but

they do cause pulmonary diseases that resemble TB.[32]

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ia.org/wiki/Mycobacterium_africanumhttp://en.wikipedia.org/wiki/Mycobacterium_canettihttp://en.wikipedia.org/wiki/Mycobacterium_canettihttp://en.wikipedia.org/wiki/Mycobacterium_canettihttp://en.wikipedia.org/wiki/Mycobacterium_microtihttp://en.wikipedia.org/wiki/Mycobacterium_microtihttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-25http://en.wikipedia.org/wiki/Tuberculosis#cite_note-25http://en.wikipedia.org/wiki/Tuberculosis#cite_note-25http://en.wikipedia.org/wiki/Tuberculosis#cite_note-26http://en.wikipedia.org/wiki/Tuberculosis#cite_note-26http://en.wikipedia.org/wiki/Tuberculosis#cite_note-26http://en.wikipedia.org/wiki/Pasteurisationhttp://en.wikipedia.org/wiki/Pasteurisationhttp://en.wikipedia.org/wiki/Pasteurisationhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-Robbins-1http://en.wikipedia.org/wiki/Tuberculosis#cite_note-Robbins-1http://en.wikipedia.org/wiki/Tuberculosis#cite_note-Robbins-1http://en.wikipedia.org/wiki/Horn_of_Africahttp://en.wikipedia.org/wiki/Horn_of_Africahttp://en.wikipedia.org/wiki/Horn_of_Africahttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-29http://en.wikipedia.org/wiki/Tuberculosis#cite_note-29http://en.wikipedia.org/wiki/Tuberculosis#cite_note-29http://en.wikipedia.org/wiki/Prevalencehttp://en.wikipedia.org/wiki/Prevalencehttp://en.wikipedia.org/wiki/Prevalencehttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-31http://en.wikipedia.org/wiki/Tuberculosis#cite_note-31http://en.wikipedia.org/wiki/Tuberculosis#cite_note-31http://en.wikipedia.org/wiki/Mycobacterium_lepraehttp://en.wikipedia.org/wiki/Mycobacterium_lepraehttp://en.wikipedia.org/wiki/Mycobacterium_lepraehttp://en.wikipedia.org/wiki/Mycobacterium_avium_complexhttp://en.wikipedia.org/wiki/Mycobacterium_avium_complexhttp://en.wikipedia.org/wiki/Mycobacterium_avium_complexhttp://en.wikipedia.org/wiki/Mycobacterium_kansasiihttp://en.wikipedia.org/wiki/Mycobacterium_kansasiihttp://en.wikipedia.org/wiki/Mycobacterium_kansasiihttp://en.wikipedia.org/wiki/Nontuberculous_mycobacteriahttp://en.wikipedia.org/wiki/Nontuberculous_mycobacteriahttp://en.wikipedia.org/wiki/Nontuberculous_mycobacteriahttp://en.wikipedia.org/wiki/Leprosyhttp://en.wikipedia.org/wiki/Leprosyhttp://en.wikipedia.org/wiki/Leprosyhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-ALA_1997-32http://en.wikipedia.org/wiki/Tuberculosis#cite_note-ALA_1997-32http://en.wikipedia.org/wiki/Tuberculosis#cite_note-ALA_1997-32http://en.wikipedia.org/wiki/File:Mycobacterium_tuberculosis.jpghttp://en.wikipedia.org/wiki/File:Mycobacterium_tuberculosis.jpghttp://en.wikipedia.org/wiki/File:Mycobacterium_tuberculosis.jpghttp://en.wikipedia.org/wiki/File:Mycobacterium_tuberculosis.jpghttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-ALA_1997-32http://en.wikipedia.org/wiki/Leprosyhttp://en.wikipedia.org/wiki/Nontuberculous_mycobacteriahttp://en.wikipedia.org/wiki/Mycobacterium_kansasiihttp://en.wikipedia.org/wiki/Mycobacterium_avium_complexhttp://en.wikipedia.org/wiki/Mycobacterium_lepraehttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-31http://en.wikipedia.org/wiki/Prevalencehttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-29http://en.wikipedia.org/wiki/Tuberculosis#cite_note-29http://en.wikipedia.org/wiki/Horn_of_Africahttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-Robbins-1http://en.wikipedia.org/wiki/Tuberculosis#cite_note-Robbins-1http://en.wikipedia.org/wiki/Pasteurisationhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-26http://en.wikipedia.org/wiki/Tuberculosis#cite_note-26http://en.wikipedia.org/wiki/Tuberculosis#cite_note-25http://en.wikipedia.org/wiki/Mycobacterium_microtihttp://en.wikipedia.org/wiki/Mycobacterium_canettihttp://en.wikipedia.org/wiki/Mycobacterium_africanumhttp://en.wikipedia.org/wiki/Mycobacterium_africanumhttp://en.wikipedia.org/wiki/Mycobacterium_bovishttp://en.wikipedia.org/wiki/Mycobacteriumhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-24http://en.wikipedia.org/wiki/Fluorescence_microscopehttp://en.wikipedia.org/wiki/Auramine-rhodamine_stainhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-Stain2000-23http://en.wikipedia.org/wiki/Ziehl%E2%80%93Neelsen_stainhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-Robbins-1http://en.wikipedia.org/wiki/Tuberculosis#cite_note-Robbins-1http://en.wikipedia.org/wiki/Acid-fast_bacillushttp://en.wikipedia.org/wiki/Phlegmhttp://en.wikipedia.org/wiki/Expectoratehttp://en.wikipedia.org/wiki/Histologyhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-Parish_1999-22http://en.wikipedia.org/wiki/In_vitrohttp://en.wikipedia.org/wiki/Host_(biology)http://en.wikipedia.org/wiki/Endosporehttp://en.wikipedia.org/wiki/Disinfectanthttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-Madison_2001-21http://en.wikipedia.org/wiki/Mycolic_acidhttp://en.wikipedia.org/wiki/Lipidhttp://en.wikipedia.org/wiki/Gram_stainhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-Niederweis2010-20http://en.wikipedia.org/wiki/Bacterial_cell_structurehttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-19http://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-18http://en.wikipedia.org/wiki/Lipidhttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-ID10-9http://en.wikipedia.org/wiki/Bacillushttp://en.wikipedia.org/wiki/Aerobic_organismhttp://en.wikipedia.org/wiki/Mycobacterium_tuberculosishttp://en.wikipedia.org/wiki/Mycobacterium_tuberculosishttp://en.wikipedia.org/wiki/Scanning_electron_micrographhttp://en.wikipedia.org/wiki/Mycobacterium_tuberculosis

8/13/2019 Risk Factors of Tb

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Risk factors

Main article:Risk factors for tuberculosis

A number of factors make people more susceptible to TB infections. The most important risk factor

globally isHIV;13% of all TB cases are infected by the virus.[6]

This is a particular problem insub-Saharan

Africa,where rates of HIV are high.[33][34]

Of people without HIV who are infected with tuberculosis, about510% develop active disease during their lifetimes;

[10]in contrast, 30% of those coinfected with HIV

develop the active disease.[10]

Tuberculosis is closely linked to both overcrowding andmalnutrition,making it one of the

principaldiseases of poverty.[7]

Those at high risk thus include: people who inject illicit drugs, inhabitants

and employees of locales where vulnerable people gather (e.g. prisons and homeless shelters), medically

underprivileged and resource-poor communities, high-risk ethnic minorities, children in close contact with

high-risk category patients, and health care providers serving these patients.[35]

Chronic lung disease is another significant risk factor.Silicosisincreases the risk about 30-fold.[36]

Those

who smokecigaretteshave nearly twice the risk of TB than nonsmokers.[37]

Other disease states can also increase the risk of developing tuberculosis. These

includealcoholism[7]

anddiabetes mellitus(threefold increase).[38]

Certain medications, such ascorticosteroidsandinfliximab(an anti-TNF monoclonal antibody) are

becoming increasingly important risk factors, especially in thedeveloped world.[7]

There is also agenetic susceptibility,[39]

for which overall importance remains undefined.[7]

Mechanism

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an_Africahttp://en.wikipedia.org/wiki/Tuberculosis#cite_note-WHO2011-6http://en.wikipedia.org/wiki/HIVhttp://en.wikipedia.org/wiki/Risk_factors_for_tuberculosis