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CISCEISC (Science) ISC Class 12
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Syllabus

Barriers to Invasion by Pathogens

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Estimated time: 9 minutes
CISCE: Class 12

Pathogen Invasion and Host Defense

  • Pathogens secrete chemical toxins after successfully entering the host, causing physiological and structural abnormalities.
  • These toxins destroy host leukocytes (white blood cells), clearing the way for the pathogen to multiply and establish an infection.
  • The host actively or passively resists the pathogen based on its genetic makeup and environmental conditions.
  • The ultimate severity of a disease is determined by the balance between the host's defence mechanisms and the pathogen's strength.
CISCE: Class 12

Key Disease Terminologies

  1. Pathogenicity: The general ability of a microorganism to cause disease in a host.
  2. Virulence: The specific capacity or degree to which a given microbial strain can produce disease.
  3. Attenuation: The process of lowering the virulence of an originally dangerous microbial strain (weakened strains are often used in vaccines).
  4. Infectivity: The ability of a pathogen to successfully overcome host defences and establish itself.
  5. Invasiveness: The capability of a pathogen to invade host tissues and actively grow within them.
  6. Toxigenicity: The ability of a microbe to produce toxins that damage or destroy host cells.
  7. Susceptibility: The host's lack of resistance to a specific pathogen, making them vulnerable to contracting the disease.
CISCE: Class 12

Historical Milestones in Immunization

  • Edward Jenner (1796): Discovered that prior exposure to a mild disease (cowpox) provided immunity against a deadly one (smallpox). He successfully tested this hypothesis by inoculating a young boy, pioneering the concept of immunisation.
  • Louis Pasteur: Expanded on Jenner's principles by using intentionally attenuated (weakened) cultures to prevent diseases like anthrax, rabies, and chicken cholera.
  • Pasteur officially coined the term vaccine (derived from the Latin word vacca, meaning cow) and the process of vaccination.
CISCE: Class 12

Key Points: Barriers to Invasion by Pathogens

  • Pathogens cause disease by producing toxins that damage host tissues and weaken host defence cells.
  • The severity of disease depends on the pathogenicity and virulence of the microorganism and the susceptibility of the host.
  • Virulence refers to the ability of a microbial strain to infect, invade tissues and produce toxins, while attenuated strains show reduced virulence.
  • Hosts resist infections through defensive mechanisms influenced by their genetic makeup and environmental conditions.
  • The principle of immunity and vaccination, discovered by Jenner and later developed by Pasteur, protects the host by using attenuated or mild forms of pathogens.
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