Pathogenesis

• Pathogen


  An agent that causes disease – either a microorganism (bacteria, protist, fungi or parasite), virus or prion
• Disease


  Any condition that disturbs the normal functioning of the body (i.e. the body can no longer maintain homeostasis)
• Illness


  A deterioration in the normal state of health of an organism (a disease may cause an illness)
• Pathogens are generally species-specific in that their capacity to cause disease (pathogenesis) is limited to a particular species
• Diseases caused by pathogens that specifically affect human hosts

  • Polio
  • Syphilis
  • Measles
  • Gonorrhoea
• Certain pathogens may cross the species barrier and be able to infect and cause disease in a range of hosts
• Zoonotic diseases (or zoonoses)


  Diseases from animals that can be transmitted to humans
• Examples of zoonotic diseases

  • Rabies (dogs)
  • Certain strains of influenza (e.g. bird flu)
  • Bubonic plague (rats)
• Methods of disease transmission

  • Direct contact
  • Contamination
  • Airborne
  • Vectors
• Direct contact – the transfer of pathogens via physical association or the exchange of body fluids
• Contamination – ingestion of pathogens growing on, or in, edible food sources
• Airborne – certain pathogens can be transferred in the air via coughing and sneezing
• Vectors – intermediary organisms that transfer pathogens without developing disease symptoms themselves