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Mycobacterium tuberculosis . Presented By: Haneen Oueis, Suzanne Midani, Rodney Rosfeld, Lisa Petty. World TB Day - March 24 th. Statistics. #1 on the list of lethal infectious diseases 2 million deaths worldwide annually Every year 8 million cases reported annually

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Mycobacterium tuberculosis

Presented By: Haneen Oueis, Suzanne Midani, Rodney Rosfeld, Lisa Petty

World TB Day - March 24th


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Statistics

  • #1 on the list of lethal infectious diseases

  • 2 million deaths worldwide annually

  • Every year 8 million cases reported annually

  • Death rate after contracting the disease, if untreated, is the same as flipping a coin


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History

  • TB has been known as Pthisis, King’s Evil, Pott’s disease, consumption, and the White Plague.

  • Egyptian mummies from 3500 BCE have the presence of Mycobacterium tuberculosis


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The Great White Plague

  • Started in Europe in 1600’s

  • Reigned for around 200 years

  • Named for the loss of skin color of those infected


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The New World

  • Infected the New World before the Europeans

  • 10% deaths in the 19th century were due to TB

  • Isolated the infected in sanitariums, which served as waiting rooms for death


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Stage 1

Droplet nuclei are inhaled, and are generated by talking, coughing and sneezing.

Once nuclei are inhaled, the bacteria are non-specifically taken up by alveolar macrophages.

The macrophages will not be activated, therefore unable to destroy the intracellular organism.

The large droplet nuclei reaches upper respiratory tract, and the small droplet nuclei reaches air sacs of the lung (alveoli) where infection begins.

Disease onset when droplet nuclei reaches the alveoli.

Disease progression- Stage 1


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Disease Progression- Stage 2

  • Begins after 7-21 days after initial infection.

  • TB multiplies within the inactivated macrophages until macrophages burst.

  • Other macrophages diffuse from peripheral blood, phagocytose TB and are inactivated, rendering them unable to destroy TB.


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Disease Progression- Stage 3

  • Lymphocytes, specifically T-cells recognize TB antigen. This results in T-cell activation and the release of Cytokines, including interferon (IFN).

  • The release of IFN causes the activation of macrophages, which can release lytic enzymes and reactive intermediates that facilitates immune pathology.

  • Tubercle forms, which contains a semi-solid or “cheesy” consistency. TB cannot multiply within tubercles due to low PH and anoxic environment, but TB can persist within these tubercles for extended periods.


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Disease Progression- Stage 4

  • Although many activated macrophages surround the tubercles, many other macrophages are inactivated or poorly activated.

  • TB uses these macrophages to replicate causing the tubercle to grow.

  • The growing tubercle may invade a bronchus, causing an infection which may spread to other parts of the lungs. Tubercle may also invade artery or other blood supply.

  • Spreading of TB may cause milliary tuberculosis, which can cause secondary lesions.

  • Secondary lesions occur in bones, joints, lymph nodes, genitourinary system and peritoneum.


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Stage 5

  • The caseous centers of the tubercles liquefy.

  • This liquid is very crucial for the growth of TB, and therefore it multiplies rapidly (extracellularly).

  • This later becomes a large antigen load, causing the walls of nearby bronchi to become necrotic and rupture.

  • This results in cavity formation and allows TB to spread rapidly into other airways and to other parts of the lung.


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Virulent Mechanisms of TB

TB mechanism for cell entry

  • The tubercle bacillus can bind directly to mannose receptors on macrophages via the cell wall-associated mannosylated glycolipid (LAM)

    TB can grow intracellularly

  • Effective means of evading the immune system

  • Once TB is phagocytosed, it can inhibit phagosome-lysosome fusion

  • TB can remain in the phagosome or escape from the phagosome ( Either case is a protected environment for growth in macrophages)


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Virulent mechanisms of TB

Slow generation time

  • Immune system cannot recognize TB, or cannot be triggered to eliminate TB

    High lipid concentration in cell wall

  • accounts for impermeability and resistance to antimicrobial agents

  • Accounts for resistance to killing by acidic and alkaline compounds in both the inracellular and extracelluar environment

  • Also accounts for resistance to osmotic lysis via complement depostion and attack by lysozyme


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Virulent Factors of TB

Antigen 85 complex

  • It is composed of proteins secreted by TB that can bind to fibronectin.

  • These proteins can aid in walling off the bacteria from the immune system

    Cord factor

  • Associated with virulent strains of TB

  • Toxic to mammalian cells


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Antibiotic Mechanisms

  • Inhibition of mRNA translation and translational accuracy (Streptomycin and derivatives)

  • RNA polymerase inhibition (rifampicin) – inhibition of transcript elongation

  • Gyrase inhibition in DNA synthesis (fluoroquinolone)


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Antibiotic Mechanism II

  • Inhibition of mycolic acid synthesis for cellular wall (isoniazid)

  • Inhibition of arabinogalactan synthesis for cellular wall synthesis (ethambutol)

  • Sterilization – by lowering pH (pyrazinamide)



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Problems with Mainstream Antibiotics

  • β–lactam inhibitors of peptidoglycan biosynthesis is not effective due to protection by mycobacterial long chain fatty acids (40 – 90 carbons) in plasma lemma

  • Need unique target for mycobacterial species - M. tuberculosis, leprae, africanum, bovis,

  • To solve antibiotic problem select something other than a cellular wall disruptor


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Resistance Mechanisms of TB

  • TB inactivates drug by acetylation – effective on aminoglycoside antibiotics (streptomycin)

  • Also, thru attenuation of catalase activity, in this way TB has developed resistance against certain drugs (asonizid)

  • TB microbe has accumulated mutations that resist antibiotic binding (rifampicin and derivatives)


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HIV is the most powerful factor known to increase the risk of TB

HIV promotes both the progression of latent TB infection to active disease and relapse of the disease in previously treated patients.

TB is one of the leading causes of death in HIV-infected people.

“The co-epidemic”HIV & TB


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Up to 70% of TB patients are co-infected with HIV in some countries.

One-third of the 40 million people living with HIV/AIDS worldwide are co-infected with TB.

Without proper treatment, approximately 90% of those living with HIV die within months of contracting TB.

HIV/AIDS is dramatically fuelling the TB epidemic in sub-Saharan Africa

TB/HIV Facts


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TB/HIV Facts countries.

  • Individual infected with HIV has a 10 x increased risk in developing TB

  • By 2000 nearly 11.5 million HIV-infected people worldwide were co-infected with M. tuberculosis

- 70% of these 11.5 million co-infection cases were in sub-Saharan Africa


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Patterns of HIV-related TB countries.

  • As HIV infection progresses CD4+ T-lymphocytes decline in number and function.

  • CD4+ cells play an important role in the body’s defense against tubercle bacilli

  • Immune system becomes less able to prevent growth and local spread of M. tuberculosis


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Reasons for Fear countries.

  • Drug resistant strains of Mycobacterium tuberculosis have developed

  • Underdeveloped countries are the most affected by TB

  • 95% of reported cases come from underdeveloped countries

  • High HIV rates in those areas contribute to the contraction of TB


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What is MDR-TB ? countries.

  • It is a mutated form of the TB microbe that is extremely resistant to at least the two most powerful anti-TB drugs - isoniazid and rifampicin.

  • People infected with TB that is resistant to first-line TB drugs will confer this resistant form of TB to people they infect.

  • MDR-TB is treatable but requires treatment for up to 2 years.

  • MDR-TB is rapidly becoming a problem in Russia, Central Asia, China, and India.


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MDR-TB in the news: countries. Man with tuberculosis jailed as threat to health - USA Today 4-11-2007

  • Russian-born man with extensively drug-resistant strain of TB, has been locked in a Phoenix hospital jail ward since July for not wearing face mask


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Blanchard, J. countries. 1996. Molecular mechanisms of drug resistance in mycobacterium tuberculosis. Annual Review of Biochemistry 65:215-39

National Institute of Allergy and Infectious Diseases: http://www.niaid.nih.gov/publications/blueprint/page2.htm

Tascon, R., Colston, M. et al. 1996. Vaccination of tuber-culosis by DNA injection. Nature Medicine Volume 2, No. 8

WHO HIV/TB Clinical Manual http://whqlibdoc.who.int/publications/2004/9241546344.pdf

http://www.scielo.br/img/revistas/mioc/v101n7/v101n7a01f02.gif

http://textbookofbacteriology.net/tuberculosis.html

http://efletch.myweb.uga.edu/history.htm

http://www.faculty.virginia.edu/blueridgesanatorium/death.htm

http://www.gsk.com/infocus/whiteplague.htm

Citations


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