| Tuberculosis (abbreviated as TB for
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| | people, and M. microti is not usually
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| Tubercle Bacillus) is a common and deadly
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| | pathogenic, although it is possible that
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| infectious disease caused by the
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| | the prevalence of M. microti infections
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| bacterium Mycobacterium tuberculosis,
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| | has been underestimated. Other pathogenic
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| which most commonly affects the lungs
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| | mycobacteria are known, such as
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| (pulmonary TB) but can also affect the
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| | Mycobacterium avium and M. kansasii;
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| central nervous system, lymphatic system,
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| | these are part of the group defined as
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| circulatory system, genitourinary system,
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| | Nontuberculous mycobacteria (NTM).
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| bones and joints.
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| | Nontuberculous mycobacteria are
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| Over one third of the world's population
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| | mycobacteria that are not part of the M.
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| now has the TB bacterium in their bodies
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| | tuberculosis complex, but cause pulmonary
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| and new infections are occurring at a
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| | diseases resembling tuberculosis.
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| rate of one per second. Not everyone who
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| | Transmission
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| is infected develops the disease and
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| | TB is spread by aerosol droplets expelled
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| asymptomatic latent TB infection is most
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| | by people with the active disease of the
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| common. However, one in ten latent
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| | lungs when they cough, sneeze, speak, or
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| infections will progress to active TB
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| | spit. These infectious droplets are 0.5
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| disease which, if left untreated, will
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| | to 5 µm in diameter and about 40,000 can
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| kill more than half of its victims. In
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| | be produced by a single sneeze. People
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| 2004, 14.6 million people had active TB
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| | with prolonged, frequent, or intense
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| and there were 8.9 million new cases and
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| | contact are at highest risk of becoming
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| 1.7 million deaths, mostly in developing
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| | infected, with an estimated 22% infection
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| countries. A rising number of people in
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| | rate. A person with untreated, active
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| the developed world contract tuberculosis
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| | tuberculosis can infect 10-15 other
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| because their immune systems are
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| | people per year. Others at risk include
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| compromised by immunosuppressive drugs,
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| | those from areas where TB is common,
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| substance abuse, or HIV/AIDS.
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| | patients immunocompromised by conditions
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| The rise in HIV infection levels and the
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| | such as HIV/AIDS, residents and employees
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| neglect of TB control programs have
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| | of high-risk congregate settings, health
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| caused a resurgence of tuberculosis, and
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| | care workers who serve high-risk clients,
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| drug-resistant strains of TB are also
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| | medically underserved, low-income
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| emerging. The World Health Organization
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| | populations, high-risk racial or ethnic
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| declared TB a global health emergency in
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| | minority populations, children exposed to
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| 1993, and the Stop TB Partnership
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| | adults in high-risk categories, and
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| proposed a Global Plan to Stop
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| | people who inject illicit drugs.
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| Tuberculosis which aims to save 14
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| | Transmission can only occur from people
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| million lives between 2006 and 2015.
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| | with active—not latent— TB disease.
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| In the past, tuberculosis was called
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| | The probability of transmission from one
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| Consumption, because it seemed to consume
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| | person to another depends upon the
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| people from within with bloody cough,
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| | quantity of the infectious droplets
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| fever, pallor, and long relentless
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| | expelled by the patient, the
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| wasting. Other names included Phthisis
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| | effectiveness of ventilation, the
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| (Greek for consumption) and phthisis
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| | duration of exposure, and the virulence
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| pulmonalis; Scrofula, affecting the
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| | of the Mycobacterium tuberculosis strain.
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| lymphatic system and resulting in swollen
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| | The chain of transmission can therefore
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| neck glands; Tabes mesenterica, TB of the
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| | be broken by isolating patients with
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| abdomen and Lupus vulgaris, TB of the
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| | active disease and starting effective
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| skin; Wasting disease; White plague,
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| | anti-tuberculous therapy.
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| because sufferers appear markedly pale;
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| | About 90% of those infected with
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| King's evil, because it was believed that
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| | Mycobacterium tuberculosis have
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| a king's touch would heal scrofula; and
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| | asymptomatic, latent TB infection
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| Pott's disease of the spine and joints.
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| | (sometimes called LTBI), with only a 10%
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| Miliary TB is an archaic term that is
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| | lifetime chance that a latent infection
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| still occasionally used, and is when the
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| | will progress to TB disease. However, if
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| infection invades the circulatory system
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| | untreated, the death rate for these
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| resulting in x-ray lesions with the
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| | active TB cases is more than 50%.
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| appearance of millet seeds. This form of
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| | TB infection begins when the mycobacteria
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| TB is now more commonly named
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| | reach the pulmonary alveoli, where they
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| disseminated TB.
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| | invade and replicate within alveolar
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| Symptoms
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| | macrophages. The primary site of
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| In the patients where TB becomes an
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| | infection in the lungs is called the Ghon
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| active disease, 75% of these cases affect
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| | focus. Bacteria are picked up by
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| the lungs, where the disease is called
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| | dendritic cells, which do not allow
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| pulmonary TB. Symptoms include a
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| | replication, although these cells can
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| productive, prolonged cough of more than
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| | transport the bacilli to local
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| three weeks duration, chest pain, and
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| | (mediastinal) lymph nodes. Further spread
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| coughing up blood. Systemic symptoms
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| | is through the bloodstream to the more
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| include fever, chills, night sweats,
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| | distant tissues and organs where
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| appetite loss, weight loss, and easy
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| | secondary TB lesions can develop in lung
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| fatigability.
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| | apexes, peripheral lymph nodes, kidneys,
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| When the infection spreads out of the
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| | brain, and bone.
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| lungs, extrapulmonary sites include the
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| | Tuberculosis is classified as one of the
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| pleura, central nervous system in
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| | granulomatous inflammatory conditions.
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| (meningitis), lymphatic system in
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| | Macrophages, T lymphocytes, B lymphocytes
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| (scrofula of the neck), genitourinary
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| | and fibroblasts are among the cells that
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| system in urogenital tuberculosis, and
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| | aggregate to form a granuloma, with
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| bones and joints in Pott's disease of the
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| | lymphocytes surrounding the infected
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| spine. An especially serious form is
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| | macrophages. The granuloma functions not
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| disseminated, or miliary tuberculosis.
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| | only to prevent dissemination of the
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| Extrapulmonary forms are more common in
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| | mycobacteria, but also provides a local
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| immunosuppressed persons and in young
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| | environment for communication of cells of
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| children. Infectious pulmonary TB may
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| | the immune system. Within the granuloma,
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| co-exist with extrapulmonary TB, which is
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| | T lymphocytes (CD4+) secrete cytokines
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| not contagious.
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| | such as interferon gamma, which activates
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| Bacterial species
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| | macrophages to destroy the bacteria with
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| The cause of tuberculosis, Mycobacterium
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| | which they are infected. T lymphocytes
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| tuberculosis (MTB), is a slow-growing
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| | (CD8+) can also directly kill infected
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| aerobic bacterium that divides every 16
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| | cells.
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| to 20 hours; this is extremely slow
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| | Importantly, bacteria are not always
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| compared to other bacteria that have
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| | eliminated within the granuloma, but can
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| division times measured in minutes. In
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| | become dormant, resulting in a latent
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| contrast, one of the fastest growing
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| | infection. Another feature of the
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| bacteria is a strain of E. coli that can
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| | granulomas of human tuberculosis is the
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| divide roughly every 20 minutes. MTB is
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| | development of cell death, also called
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| not classified as either Gram-positive or
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| | necrosis, in the center of tubercles. To
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| Gram-negative because it does not have
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| | the naked eye this has the texture of
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| the chemical characteristics of either.
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| | soft white cheese and was termed caseous
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| If a Gram stain is performed, MTB either
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| | necrosis.
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| stains very weakly Gram-positive, or not
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| | If TB bacteria gain entry to the
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| at all. MTB is a small rod-like bacillus
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| | bloodstream from an area of tissue damage
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| which can withstand weak disinfectants
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| | they spread through the body and set up
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| and can survive in a dry state for weeks.
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| | many foci of infection, all appearing as
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| Normally, the bacteria can only grow
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| | tiny white tubercles in the tissues. This
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| within a host organism, so in vitro
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| | severe form of TB disease is most common
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| culture of M. tuberculosis took a long
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| | in infants and the elderly and is called
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| time to develop, but is now a routine
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| | miliary tuberculosis. Patients with this
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| laboratory procedure.
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| | disseminated TB have a fatality rate of
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| MTB is identified microscopically by its
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| | approximately 20%, even with intensive
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| staining characteristics: it retains
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| | treatment.
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| certain stains after being treated with
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| | In many patients the infection waxes and
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| acidic solution, and is thus classified
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| | wanes. Tissue destruction and necrosis
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| as an "acid-fast bacillus" or AFB. In the
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| | are balanced by healing and fibrosis.
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| most common staining technique, the
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| | Affected tissue is replaced by scarring
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| Ziehl-Neelsen stain, AFB are stained a
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| | and cavities filled with cheese-like
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| bright red which stands out clearly
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| | white necrotic material. During active
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| against a blue background. Acid-fast
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| | disease, some of these cavities are
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| bacilli can also be visualized by
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| | joined to the air passages bronchi and
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| fluorescent microscopy, and by an
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| | this material can be coughed up. It
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| auramine-rhodamine stain.
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| | contains living bacteria and can
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| The M. tuberculosis complex includes 3
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| | therefore pass on infection. Treatment
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| other mycobacteria which can cause
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| | with appropriate antibiotics kills
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| tuberculosis: M. bovis, M. africanum and
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| | bacteria and allows healing to take
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| M. microti. The first two are very rare
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| | place. Upon cure, affected areas are
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| causes of disease in immunocompetent
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| | eventually replaced by scar tissue
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