Pathology

Pathology is defined as the scientific study of the nature of disease and its causes, processes, development, and consequences. Also known as pathobiology.

Before the doctors told us of the danger of a kiss
I considered kissing you nothing short of bliss
But now I know the danger and I sit and sigh and moan --
Six billion small bacteria, and I thought we were alone.

A pathogen is a disease causing agent, such as bacteria, virusus, fungi or parasites.

This unit will focus on 3 areas of Pathology:

  • virology
  • bacteriology
  • parasitology

Definitions

Host - organism which provides nutrients, etc. to another organism
Parasite - organism which lives at the expense of (and may even harm) its host; the parasite is generally smaller than the host and is metabolically dependent upon it
Disease - an upset in the homeostasis of the host, resulting in generation of observable changes
symptom - evidence of damage to the host (headache)
Infectious disease - one in which detrimental changes in health of the host occur as a result of damage caused by a parasite, can be transmitted
Virulence - a measure of pathogenicity, which is the ability to cause disease (a microorganism that causes disease is virulent)
Epidemic - when a disease affects a community
Pandemic - when a disease affects the world

Disease Categories

Food and Water borne - pathogen is in a food or water source
Blood Borne - carried in blood or other bodily fluids
Sexually Transmitted - transmitted by sexual contact
Zoonotic - carried by animals
Airborne - carried by the air, often affect respiratory tract

Organizations Dealing with Health

Centers for Disease Control (CDC)
World Health Organization (WHO)
US Department of Health and Human Services (HHS)

The Germ Theory (around 1860)

  • single most important contribution by the science of microbiology to the general welfare of the world's people
  • The theory that microorganisms may be the cause of some or all disease.
  • Key to developing the germ theory of disease was a refutation of the concept of spontaneous generation.
  • Specific aseptic techniques are employed to avoid microbial contamination
  • Method of prevention of spoilage of liquid foodstuffs - Pasteurization

Koch's Postulates

If a microorganism is the causative agent of an infectious disease, it must be:

  • Present in every case of the disease, but absent from the healthy host
  • Isolated and grown in pure culture
  • Able to Cause the disease when a pure culture is inoculated into a healthy host
  • Re-isolated from the host that was inoculated with the pure culture

Steps in Pathogenesis To cause disease, a pathogen must:

  • Contact the host - be transmissible
  • Colonize the host - adhere to and grow or multiply on host surfaces
  • Infect the host - proliferate in host cells or tissues
  • Evade the host defense system - by avoiding contact that will damage it
  • Damage host tissues - by physical (mechanical) or chemical means