Tuberculosis

January 28th, 2008

Jasemine Yang and Tamara Bodnar

M. tuberculosis

A Brief History of Tuberculosis (TB)

- Tuberculosis (phthisis) described since the time of Hippocrates (460 BC - 370 BC)

- 1689: Doctor Richard Morton used the term “consumption” to denote TB.

- Second half of the 17th century: high death rates from TB in Europe.

- 1722: Doctor Benjamin Marten proposed that TB could be transmitted in the air and described TB as being caused by “wonderfully minute living creatures”

- End of 19th century to the start of 20th century: Principal cause of death in Europe was TB.

- The romantic Era of TB

“Queen Guinevere” painted by William Morris

A Brief History of Tuberculosis (TB)

- 1865 Jean-Antoine Villemin: confirmed that TB is contagious.

- Robert Koch:- 1882: Isolated and cultured M.

tuberculosis.- 1890: Announced the discovery of

tuberculin.- Developed staining methods used to

identify the bacteria.- 1905: Received the Nobel Prize

- Bacteriologist Paul Ehrlich developed Ziehl- Neelsen staining.

- Late 1800’s: Edward Livingston Trudeau established “Adirondack Cottage Sanatorium”, first TB sanatorium in the US.

Visualization of M. tuberculosis using the Ziehl-Neelsen stain

- 1896 Theobald Smith demonstrated that bovine TB is caused by M. bovis.

- 1908 Albert Calmette and Camille Guérin isolated M. bovis and grew it in ox bile.

- Identified a morphological variant of M. bovis found to be avirulent, conferred immunity against M. tuberculosis.

– Lead to the BCG vaccine (bacilli Calmette-Guérin).

- Development of antibiotics to combat infection:

– 1947: streptomycin, 1952: isoniazid– The majority of drugs used to combat

infection were identified between 1945 and 1967.

– No new drugs developed since the 1980’s

- Reoccurrence of TB for two main reasons:1)HIV/AIDS pandemic 2)Development of drug

resistance

A Brief History of Tuberculosis (TB)

M. bovis

- Reservoir: Humans- Transmission: Airborne disease (aerosol

transmission) - Symptoms:

Latent TB infection: Active TB infection:No symptoms Bad cough *Cannot spread TB Coughing up blood/sputum

Chest pain Loss of appetite Weight loss

Fever Chills Night sweats Swollen glands *Contagious

Tuberculosis in Humans

Extra-pulmonary TB: Symptoms depend on location of infectionGeneral symptoms: fatigue, fever, loss of appetite, weight loss.

TB of lymph nodes: swelling of lymph nodesTB meningitis: neurological symptoms including headacheSpinal TB: Mobility impairments, pain

Mycobacterium Tuberculosis

General Characteristics- Family – Myobacteria- Gram-positive aerobic rod-shaped bacilli- “Acid fast” bacteria- Lack of spore formation and toxin production- No capsule, flagellum (non-motile)- Generation time of 18- 24 hours but requires

3-4 weeks for visual colonies

Pathological Features- Principle cause of Human Tuberculosis- Intracellular pathogen (alveolar

macrophages)- Waxy, thick, complex cellular envelope - Cell envelope components ex) sulfolipids - Produces tubercles, localized lesions of M.

tuberculosis

SEM of M. tuberculosis

M. Tuberculosis (stained in purple)

Mycobacterial Cellular Envelope

General Features- Thick, waxy and complex- Higher fluidity in more external

regions than internal regions- Relatively impermeable to

hydrophilic solutes- Contain porins (selective cationic

channels)

Main Components- Peptidoglycan contains N-glycolylmuramic acid instead of N-acetylmuramic acid

- Arabinogalactan- Mycolic Acids (60% of cellular

envelope)- Lipoarabinomannan (LAM)

Mycobacterial Cellular Envelope

Contribution of Mycobacterial Cellular Envelope to Pathogenesis

Resistance to Drying and Other Environmental Factors

- Thick, waxy nature of cellular envelope protects M. tuberculosis from drying, alkali conditions, and chemical disinfectants

- Hinders entrance of antimicrobial agentsEntry into Host Cells- Lipoarabinomannan (LAM) binds to mannose

receptors on alveolar macropages leading to entry into the cell

Interference of Host Immune Response- Glycolipids and sulfolipids decrease the effects of oxidative

cytotoxic mechanism- Inhibition of phagosome and lysosome fusion inside

macrophage- Waxy cellular envelope prevents acidification of the bacteria

inside the phagosome

Factors Affecting Pathogenicity

Active Infection- Only individuals with an active infection

can transmit the disease

Transmission- Aerosolized droplets need to be <10μm

in order to evade the ciliated epithelium of the lung to establish infection in the terminal alveoli

Growth & Structure- Only require a very few number of

bacteria to establish an infection (1-10 bacteria)

- Slow generation time

M. Tuberculosis in sputum

(stained in red)

Variability of Infection Rates

Exposure Time- Most infected individuals expel relatively few bacilli,

transmission of TB usually occurs only after prolonged exposure to someone with active TB.

- On average, 50% of people are likely to become infected with TB if they spend 8hrs/day for six months or 24hrs/day for two months working or living with someone with active TB.

Health of Individuals- Active TB typically occur in individuals whose immune

systems have been weakened by age, disease, improper nutrition or use of immunosuppresive drugs.

Tuberculosis – Disease Progression

Primary Infection

In healthy individuals…

- M. tuberculosis phagocytosed by alveolar macrophages leading to intracellular proliferation and tubercle formation

- Cell-mediated response develops and eliminates most of the bacilli in 2-6 weeks

- Commonly asymptomatic

OR

- M. tuberculosis can remain dormant intracellularly

Tuberculosis – Disease Progression

Primary Infection

Immunocomprimised Individuals…

- Infection leads usually leads to progressive primary tuberculosis, where the pathogen breaks out of the tubercles in the alveoli and cause active disease

- Active disease leads to chronic inflammation

- Death of pathogen and pulmonary cells can lead to Gohn complex and granuloma formation

- May lead to extrapulmonary tuberculosis (TB infection outside the lung in the CNS and lymph nodes)

Latent Tuberculosis Infections- Following exposure to TB: Inhaled bacilli usually

destroyed by host’s immune system (90-95% of the time).

- Healthy person: Recruitment of T-cells and macrophages which results in controlling the infection.

- Some bacilli can establish infection in macrophages (phagosomes) leading to host immune response

- Bacilli forced into an inactive (latent), non-replicating state.

- Survive intracellularly: prevent phagosome-lysosome fusion.

- Infection contained but not eradicated.

- The dormant bacteria are still viable, can be re-activated: Approximately 10% of latent infections will develop into active TB if left untreated.

- Factors that lead to re-activation of the bacteria: HIV co-infection, aging, cancer, diabetes etc

M. Tuberculosis colonies

Tuberculosis – Disease Progression

Note…- Infection does not mean disease!- Infection can lead to active disease or dormant state of

pathogen- Active disease develops differently (Healthy individuals

VS. Immunocomprimised individuals)

Summary of TB Infection in Alverolar Macrophages

http://www.nature.com/nrmicro/animation/imp_animation/index.html

Antibacterial chemotherapy:- Combination of first and second line drugs

for the first 2 months which could include:- Isoniazid- Rifampicin- Pyrazinamide- Streptomycin or Ethambutol

- Next 4 months, combination of:- Isoniazid- Rifampicin

Treatment

- Early resistance to isoniazid: other first-line drugs such as ethambutol, streptomycin, pyrazinamide and fluoroquinolones can be added to drug arsenal (treatment period also extended).- These drugs are relatively effective in killing the bacteria, however, they also produce a wide variety of side effects.

First line drugs:- Bactericidal agents: kill active bacteria, important in the

early stages of infection.

Second line drugs:- Bacteriostatic: hinder bacterial growth.

- Strengthen treatment in the case of resistant bacteria.- Less efficient and generally more toxic than first line

drugs.

Inappropriate chemotherapy:- Monotherapy (single drug treatment)- Decreased treatment period- Low absorption of drugs

Treatment

Drug Bactericidal orBacteriostatic

Mechanism of Action Mutation Rate

Side Effects

Isoniazid Bactericidal to rapidly dividing bacteria and bacteriostatic to slowly dividing bacteria

Pro-drug: activated by a bacterial catalase.Inhibits enoyl-ACP reductase (key enzyme in fatty acid synthesis, different than equivalent mammalian enzymes)

1 in 105 - 106 Rash, abnormal liver function, anemia, peripheral neuropathy, mild CNS effects

Rifampicin Bactericidal Inhibits transcription by RNA polymerase

1 in 108 Fever, immune reactions, GI irritation, liver damage, can cause tears and urine to turn red/orange

Streptomycin Bactericidal Inhibits initiation of protein synthesis

1 in 108 - 109

Damage to the ears, nausea, rash, vomiting, vertigo

Ethambutol Bacteriostatic

Prevents formation of the cell wall

1 in 107 Decrease in visual acuity, colourblindness and other visual defects, joint pain, nausea, vomiting, fever, malaise, headache, dizziness

Fluoroquinolones

Bactericidal Act manly on DNA gyrase (DNA gyrase: introduces negative supercoils into DNA)

Tendon damage, heart problems, swelling of face and throat, shortness of breath, rash, loss of consciouness

Pyrazinamide Bacteriostatic, Bactericidal

Accumuates causing cellular damage

Joint pain, nauseau, vomiting, rash, malaise, fever, photosentivity

Treatment

- M. tuberculosis: naturally resistant to certain antibiotics due to presence of:

- Drug-modifying enzymes- Drug-efflux systems- Hydrophobic cell wall

- Mycobacteria undergo natural mutations which can lead to development of drug resistance.

- TB is treated by administration of combination chemotherapy: decreases probability of development of drug resistance.

- Development of increasingly resistant strains mainly due to: Patient non-compliance

Drug Resistance and Tuberculosis

MDR: Multidrug-resistant strains:- Strains of tuberculosis resistant at least to rifampicin and isoniazid.- Mortality rate: 40-60%- Estimated that 50 million people are infected with MDR-TB.- MDR-TB is approximately 125 times more expensive to treat than

drug susceptible TB.

MDR and XDR Tuberculosis

XDR: Extensively-drug resistant strains:- Strains of tuberculosis resistant to rifampicin, isoniazid and at least three of the following classes of second-line drugs: aminoglycosides, polypetides, fluoroquinolones, thioamides, cycloserine and para-aminosalicylic acid.

- Emergence due to lack of patient compliance during TB treatment and inappropriate administration of TB drugs.

- Results in more aggressive forms of TB.- Drug resistance does not increase infectiousness. - MDR and XDR-TB: uncommon in developing nations

lacking TB drugs (high drug-susceptible TB rates)- MDR and XDR-TB rates are higher in developed nations

with access to anti-TB drugs.

MDR and XDR Tuberculosis

- HIV pandemic has reversed much of the progress made in the past few decades in combating TB.

- People with latent TB have a 10-20% of developing active TB in their lifetime. People with HIV and latent TB are 100 times more likely to develop active TB.

- HIV/AIDS leads to a compromised immune system:- HIV infects CD4+ T cells, macrophages, dendritic cells.- Result: decreased CD4+ T cells due to apoptosis of infected cells,

CD8+ T cell mediated killing of infected cells

- The numbers of CD4+ T cells progressively decline (loss of cell-mediated immunity) and the body is much more susceptible to infection

Tuberculosis and HIV/AIDS

T cell

- A person with HIV/AIDS will have a harder time fighting off the M. tuberculosis infection due to a compromised immune system.

- HIV infection can cause latent M. tuberculosis infection to become reactivated.

- TB is the leading cause of death for people with HIV/AIDS: mean survival rate is 430 days.

- MDR and XDR-TB and HIV/AIDS:- Additional symptoms: excessive

weight loss, respiratory problems (including the formation of lesions in the lungs).

- Mean survival rate: 45 days.

Tuberculosis and HIV/AIDS

The WHO has developed a “Stop TB Strategy” outlining some the issues that need to be addressed in order to stop the spread of disease:

Discussion: The Challenges of TB Control

-Expansion and enhancement:

-Legistlation/planning/human resources/management/training

-Drug Resistance Surveillance (DRS)

-TB treatment and program management guidelines

-An effective drug supply and management system

-Global Drug Facility

-Revised TB recording and reporting forms

-Electronic recording and reporting systems

-Global TB Control Report

-TB epidemiology and surveillance online workshop

-Contribute to health system strengthening

-Engage all care providers

-Empower people with TB

-Community and patient involvement in TB care

-Address TB/HIV, MDR/XDR-TB and other challenges:

-TB challenges

-MDR-TB

-XDR-TB

-TB/HIV

-TB and air travel

-TB and poverty

-TB and gender

-TB and prisons

-Enable and promote research:

-Drug research

-Vaccine research

-M. tuberculosis research

-Development of new diagnostic tools for detecting latent, pulmonary and extra-pulmonary TB.

Discussion: The Challenges of TB Control

• What do you consider the top 5 most important issues?

• Are there any you feel are unimportant or relatively unimportant?

• Which do you feel would be the hardest to implement or attain?

From this list…

The WHO has multiple goals concerning the control of TB including:

- “By 2005: detect at least 70% of new sputum smear-positive

TB cases and cure at least 85% of these cases”.- “By 2015: reduce prevalence of and death due to TB by 50%

relative to 1990”.- “By 2050: eliminate TB as a public health problem (<1 case

per million population)”.

• What key issues need to be resolved and what developments need to occur in order to reach these goals? Start by examining the “Stop TB strategy” list.

Discussion: The Challenges of TB Control

The WHO has multiple goals concerning the control of TB including:

- “By 2005: detect at least 70% of new sputum smear-positive

TB cases and cure at least 85% of these cases”.- “By 2015: reduce prevalence of and death due to TB by 50%

relative to 1990”.- “By 2050: eliminate TB as a public health problem (<1 case

per million population)”.

• What key issues need to be resolved and what developments need to occur in order to reach these goals? Start by examining the “Stop TB strategy” list.

Discussion: The Challenges of TB Control

• Based on these graphs from the WHO, what do you think the correlation is between gender and rates of tuberculosis infection?

• How should this be taken into consideration when planning programs against TB?

Discussion: The Challenges of TB Control

• Why do you think there are more TB-dedicated facilities at the national or provincial level?

• Do you think this may have an effect on the prevalence of tuberculosis in these high-burden countries?

Discussion: The Challenges of TB Control

- Deadliest infectious diseases affecting humans.- Approximately 1/3 of the world population is

infected with M. tuberculosis.- 8-10 million new cases of TB per year.- Leading cause of death among people with

HIV/AIDS.- Greatest infectious killer of women of child-bearing

age.- Results in approximately 3 million deaths per

year.- 26% of preventable deaths are due to TB.- 7% of all deaths are due to TB.

- New anti-TB agents needed to combat TB due to high prevalence of drug-resistant strains.

- In 1993 the WHO declared TB a “global public health emergency” (only disease thus far to be given this designation).

Why Does TB Need Global Attention?