Ch. 35 - Infection

• infection


  a parasite growing and multiplying within a host that may or may not result in infectious disease
• pathogen


  any parasitic organism causing infectious disease; can be primary or opportunistic
• chain of infection


  agent identity, virulence of agent, dose of agent, means of exposure to agent, and susceptibility of host to agent
• virulence factors


  allow a pathogen to outcompete host cells and resist their defenses
• toxigenicity


  some microbes possess toxins and can result in toxemia
• signs


  objective changes in the body that can be directly observed
• symptoms


  subjective changes experienced by the patient
• disease syndrome


  set of characteristic signs and symptoms
• incubation period


  period after pathogen entry before any signs and symptoms
• prodromal stage


  onset of signs and symptoms but not clear enough for diagnosis
• pathogenicity islands


  virulence factors on large segments on chromosomal or plasmid DNA that increase virulence; absent in nonpathogenic members, have common sequence characteristics, and can be spread through horizontal transfer of genes
• adherence

  mediated by special molecules called adhesins or structures like pili and fimbriae that bind to a complementary receptor on the host cell
• colonization


  a site of microbial reproduction within/on the host that does not necessarily result in tissue damage
• invasion


  spreading to adjacent tissues by active (lytic attacks) or passive (wound, bites) penetration
• bacteremia


  presence of viable bacteria in the blood
• septicemia


  pathogens or their toxins in the blood
• exotoxins


  proteins secreted by gram-negative pathogens that travel from the site of infection and are highly lethal; AB, superantigens, membrane-disruptors
• AB exotoxins


  consists of A subunit responsible for toxic effect and B subunit that binds to specific target cells
• endotoxins


  LPS (lipid A) in gram-negative cell wall can be toxic to hosts and is released when the organism lyses
• transmission


  direct contact is less virulent, vector-borne is highly virulent for host but benign for vector, and the greater the ability to survive outside of the host = more virulent
• tropism


  pathogen must make contact with appropriate host tissue and specific cell surface receptors
• infectious dose


  the number of pathogens that will infect 50% of an experimental group of hosts in a specified time
• lethal dose


  the dose that kills 50% of experimental animals within a specified period
• susceptibility


  main factors are defense mechanisms of host and the pathogenicity of pathogen; nutrition, genes, and stress also play a role