Intro to Infectious Disease Flashcards
What is a pathogen, and what is the difference between primary and opportunistic?
Any disease-causing microorganism
Primary - Cause disease in any host
Opportunistic - only cause disease in hosts with impaired or damaged defense mechanisms
What is virulence?
The ability of an organism to cause disease
avirulent organisms can not or ordinarily do not cause disease
What are three general routes of transmission for disease-causing agents?
Exogenous human to human
Exogenous animals to human (zoonotic infections)
Endogenous agents part of normal flora
What are three methods of human-human transmission?
Respiratory or salivary spread (sneezing)
Fecal-Oral
Venereal
What are three methods of arthropod-borne and zoonotic infections?
Vector (biting arthropod)
Vertebrate reservoir
Vector-vertebrate reservoir
What are fomites?
Inanimate objects which can harbor microorganisms
E.g. infant toys, toothbrushes
What is the most common source of human infections?
Normal flora
They are moved from their normal habitat and invade areas which are normally sterile (blood, muscle, alveoli)
What is the most complex source of microorganisms in the body?
Large Intestine
What are the beneficial effects of normal flora?
Production of nutrients (e.g. Vit K)
Occupation of habitat (prevents occupation by pathogens)
Elaboration of bacterial toxins
Stimulation of immune response
What are Bacteriocins?
High pH, toxic bacterial proteins that kill other bacteria
What are general mechanisms underlying opportunistic infection?
Comprised Host
Breach of host surfaces
Use of antibiotics - wipe out intestinal flora
What are Koch’s Postulates?
Bacterium found in all diseased people, in affected body parts
Bacterium isolated from the lesions of an affected persons and maintained in pure culture
Pure culture, inoculated into human or animal, should reproduce the disease symptoms
Same bacterium should be reisolated from the infected animal or human
What are limitations to Koch’s Postulates?
Ignores host susceptibility and resistance
Importance of being able to culture bacterium, many can’t be cultured
Variability in virulence of single bacterial species
Ethics of inoculating humans with pathogens
Polymicrobial infections
What are bacteria?
Unicellular prokaryotic organisms
Most have cell walls
What are Fungi?
Eukaryotes with a nucleus, organelles, and a cell wall
Include yeasts, molds, and dimorphic fungi
What is the difference between yeasts and molds?
Yeasts are unicellular
Molds are multicellular or filamentous
What is the microbial definition of parasites?
Unicellular or Multicellular eukaryotic organisms that require a living host for at least part of their life cycle and cause disease in the host
This definition excludes bacteria and viruses
What are viruses?
Intracellular parasites that lack cell structure
Generally consist of nucleic acid genome surrounded by a protein coat (capsid)
What are the two types of viral infection?
Lytic cycle - one or a few viruses infect a cell, replicate within and produce 1000s viruses that are released by lysis of the host cell
Persistent or Latent infections - animal cells are not lysed by rather harbor the viral genome or allow the replication of low number of viruses
What are prions?
Infectious agents consisting only of protein
E.g. Bovine Spongiform Encephalopathy (Mad Cow), Scrapie, Creutzfeldt-Jakob
What are viroids?
Consist of RNA genome without any protein components (Hep Delta)
