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What is the primary transmission method for Mycobacterium tuberculosis?
Which of the following subgroups of the Mycobacterium tuberculosis complex is primarily known to infect seals and sea lions?
What is the approximate percentage of cases where other organs are involved in tuberculosis?
Which species of Mycobacterium is considered the most common and important for tuberculosis?
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What characteristic of Mycobacterium tuberculosis allows it to resist the decolorization by acid alcohol during staining?
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What percentage of untreated tuberculosis cases may be fatal within five years?
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Which feature of Mycobacterium tuberculosis is critical for its survival within macrophages?
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Which of the following statements about tuberculosis treatment is accurate?
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What is a significant reason for the increase in tuberculosis cases during the 1980s-90s in industrialized countries?
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Which country accounted for one of the highest shares of new tuberculosis cases as reported in 2019?
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Which of the following defines XDR-TB?
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What percentage of MDR-TB cases may potentially be XDR-TB but remain undiagnosed?
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How are droplet nuclei significant in the transmission of tuberculosis?
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Which type of TB is defined by resistance to at least isoniazid and rifampin?
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What is the primary reason for the undiagnosed cases of TB in many regions worldwide?
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What percentage of tuberculosis cases were reported from low and middle-income countries in 2019?
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Study Notes
Tuberculosis Introduction
- One of the oldest diseases known to infect humans, dating back approximately 70,000 years in Africa.
- The leading cause of infectious death globally.
- Primarily affects the lungs, but can impact other organs in up to one-third of cases.
- Curable with proper treatment for drug-susceptible strains.
- Untreated, the disease can be fatal within five years in 50-65% of cases.
- Transmission occurs via airborne spread of droplet nuclei produced by patients with infectious pulmonary tuberculosis.
Etiologic Agent
- Caused by the Mycobacterium tuberculosis complex, a group of eight distinct subgroups within the Mycobacteriaceae family.
- M. tuberculosis is the most common and significant subgroup.
- M. africanum is found in West, Central, and East Africa.
- M. bovis and M. caprae are zoonotic members. M. bovis is the bovine tubercle bacillus, characteristically resistant to pyrazinamide and transmitted through unpasteurized milk.
- M. pinnipedii affects seals and sea lions in the Southern Hemisphere.
- M. mungi affects banded mongooses in southern Africa.
- M. orygis infects oryxes and other Bovidae in Africa.
- M. microti is the "vole" bacillus, a less virulent organism.
- M. canetti is a rare, East African strain with unusual smooth colonies on solid media, believed to be closely related to a supposed progenitor type.
M. tuberculosis Characteristics
- Rod-shaped, non-spore-forming, thin aerobic bacteria measuring 0.5 μm by 3 μm.
- Acid-fast bacilli (AFB): retain stain after decolorization with acid alcohol due to high mycolic acid content.
- Mycolic acids are long-chain cross-linked fatty acids that contribute to the cell wall's low permeability, reducing the effectiveness of some antibiotics.
- Lipoarabinomannan, a component of the cell wall, plays a role in host interaction and allows M. tuberculosis to survive within macrophages.
Epidemiology
- WHO reported 7.1 million new TB cases in 2019, with an estimated 10 million new cases.
- 97% of cases were reported from low and middle-income countries.
- Eight countries accounted for two-thirds of all new cases: India, Indonesia, China, the Philippines, Pakistan, Nigeria, Bangladesh, and South Africa.
- TB cases increased in industrialized countries during the 1980s and 1990s due to:
- Immigration from regions with high TB incidence.
- The spread of the HIV epidemic.
- Social problems like urban poverty, homelessness, and drug abuse.
- Dwindling TB services.
TB Incidence and Mortality
- TB incidence rates have stabilized or declined since the 2000s, with an average decrease of 1.7% per year.
- Estimated TB mortality rates in HIV-negative individuals in 2018 were highest in Africa.
Drug-Resistant TB
- RR-TB (rifampin-resistant TB): Resistant to rifampicin.
- MDR-TB (multidrug-resistant TB): Resistant to at least isoniazid and rifampicin.
- XDR-TB (extensively drug-resistant TB): Resistant to powerful second-line anti-TB drugs such as fluoroquinolones and at least one injectable drug from the group of amikacin, kanamycin, and capreomycin.
- Only 44% of MDR-TB cases were diagnosed due to limited culture and drug susceptibility testing (DST) capacity in many parts of the world.
WHO's New Drug-Resistant TB Definitions
- Pre-XDR-TB: MDR/RR-TB with resistance to any fluoroquinolone.
- XDR-TB: MDR/RR-TB with resistance to any fluoroquinolone and at least one additional Group A drug (levofloxacin, moxifloxacin, bedaquiline, or linezolid).
- Approximately 6.2% of MDR-TB cases could potentially be XDR-TB, but remain undiagnosed due to limited testing capabilities.
Exposure to TB Infection
- Droplet nuclei, aerosolized by coughing, sneezing, or speaking, are the most common mode of transmission.
- Skin or placental transmission is rare and insignificant.
- Tiny droplets quickly dry, and smaller droplets (90%) are trapped in the upper airways and expelled by ciliated mucosal cells.
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Description
Explore the history, causes, and effects of tuberculosis, one of humanity's oldest diseases. This quiz covers its transmission, the etiologic agents involved, and the impact of treatment on the disease's outcome. Test your knowledge on this significant infectious disease and its challenges.
