Infection and Immunity Quiz

Infection and Immunity

• Host: An organism that provides nutrients to another organism.
• Parasite: An organism that lives at the expense of its host, potentially harming it. Parasites are typically smaller and metabolically dependent on their host.
• Disease: A disruption of homeostasis in the host, resulting in observable changes.
• Symptom: A subjective indication of damage to the host (e.g., headache, anorexia).
• Sign: An objective indication of damage to the host (e.g., fever, rash, vomiting).
• Infectious Disease: A disease resulting from damage caused by a parasite.
• Pathogen: A microorganism capable of causing disease.
• Virulence: A measure of pathogenicity (ability to cause disease).
• Virulent: Microorganisms that readily cause disease; only a small amount needed to initiate and sustain infection.
• Opportunistic: Microorganisms that don't typically cause disease but can cause disease if they are introduced into a location where they're not usually found (like inside host tissues), even if they usually inhabit the host. These organisms are often part of the host's normal microbiota.
• Avirulent: Microorganisms that do not cause disease.
• Attenuated: Microorganisms with a reduced ability to cause disease.

Koch's Postulates

• If a microorganism is the causative agent of an infectious disease, it must:
  • Be present in every case of the disease, but absent from healthy hosts.
  • Be isolated and grown in pure culture.
  • Cause the disease when a pure culture is introduced into a healthy host.
  • Be re-isolated from the infected host.

Steps in Pathogenesis

• To cause disease, a pathogen must:
  • Contact the host (be transmissible).
  • Colonize the host (adhere and multiply on host surfaces).
  • Infect the host (proliferate in host cells or tissues).
  • Evade the host's defense system (avoiding contact that causes damage).
  • Damage host tissues (physically or chemically).

Virulence Factors

• Factors that influence virulence in a microorganism:
  • Adhesins: Promote attachment to host cells.
    • Examples: pili used by Escherichia coli and Neisseria gonorrhoeae to attach to urethral cells. Salmonella and Escherichia coli use pili to attach to intestinal cells.

Definition of Antigen and Antibody

• Antigen: Any substance capable of inducing an immune response when introduced into an organism.
• Antibody: A protein (immunoglobulin) produced by an organism in response to stimulation by an antigen.