Infection and Immunity Quiz

Study Notes

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.

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.

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.

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.