Week 1: Infection

• Transmission of disease


  Passing of the pathogen from the reservoir of the infection through a portal of exit to a susceptible host through a portal of entry by a circumscribed mode of transmission
• Infectious Disease - Bacteria


  • Significant cause of morbidity and mortality in the United States and worldwide
  • Pathogens have unique characteristics that influence their ability to cause disease
  • Bacteria produce exotoxins or endotoxins
  • Exotoxins can damage the plasma membranes of host cells or can inactivate enzymes critical to protein synthesis (cause direct injury)
  • Endotoxins activate the inflammatory response and produce fever (cause indirect injury)
  • Septicemia is the proliferation of bacteria in the blood
  • Vasoactive enzymes released - Hypotension occurs due to leakage from increased permeability in blood vessels (septic shock)
• Infectious Disease - Viruses


  • Viruses enter host cells and use the metabolic processes of host cells to proliferate and cause disease
  • Results in decreased protein synthesis, disruption of lysosomal membranes, synthesis of viral nucleic acids (form inclusion bodies), alteration of antigenic properties of the host cell (evade immune system), transformation of host cells into cancerous cells, promotion of bacterial infection
  • Life cycle of Virus is 3 mins
• Antigenic Drift


  Minor variations in viral nucleic acids due to mutations
• Antigenic Shift


  Major variations in viral nucleic acids due to mutations
• Antigenic drift


  Individuals usually have partial protection again minor variations in viruses (if previous antibodies are present)
• Antigenic shift


  Previous protection may not exist and can lead to pandemics
• Infectious Disease - Fungus


  • Diseases caused by fungi are called mycoses
  • Occur in two forms: yeasts (spheres) and molds (filaments or hyphae)
  • Fungi release toxins and enzymes that are damaging to tissue
  • Dermatophytes are fungi that infect skin, hair, and nails with diseases such as ringworm and athlete's foot
  • Candida albicans is the most common cause of fungal infections in humans
• Infectious Disease - Parasites


  • Parasitic microorganisms range from unicellular protozoa to large worms
  • Common causes of infection worldwide
  • Parasitic and protozoal infections are rarely transmitted from human to human
  • Infection mainly spreads through vectors (e.g., by mosquito bites) or through contaminated water or food (i.e., malaria, Chagas disease, sleeping sickness, and leishmaniasis)