Pathology is defined as the scientific study of the nature of disease and its causes, processes, development, and consequences. A pathogen is a disease causing agent, such as bacteria, viruses, fungi or parasites.
This unit will focus on 3 areas of Pathology:


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
Pathogen - the disease causing agent (virus, bacteria, fungus..etc)
quarantineVector - intermediate carrier of disease (mosquito)

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
Endemic - Any disease with a low to moderate incidence rate in the population, such a the common cold

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

Warm Up Exercises for Discussion

1. Name as many diseases as you can think of, star the ones that you would consider to be *infectious*.

2. Come up with a definition and example for each of the word pairs (small groups)

Disease and Infectious Disease
Water-borne and Blood Borne
Antibiotic and Antiseptic
Vaccine and Antibiotic
Parasite and Host
Immunity and Resistance
Virus and Bacteria

Common-Source - disease that infect populations from a contaminated source, such as water
Host-to-Host - diseases that are transferred directly from infected people (or animals)

Organizations Dealing with Health - Centers for Disease Control (CDC), World Health Organization (WHO), US Department of Health and Human Services (HHS),  U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID)

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

Basically, Robert Koch established a scientific method for establishing the cause of a disease.  In doing so, he pioneered the field of microbiology.  He received a Nobel Prize in 1905 for isolating bacteria that caused anthrax, tuberculosis and cholera. 

Steps in Pathogenesis
To cause disease, a pathogen must:


Milestones in the History of Medicine

When Who What
1796 Edward Jenner Smallpox vaccine (though they didn't understand how or why it worked). Tested it on his own child.
1850 Ignaz Semmelweis Advocated washing hands to prevent spread of childbed fever
1862 Louis Pasteur Disproved spontaneous generation, supported the Germ Theory
1867 Joseph Lister Implemented the sterilization of medical instruments and washing of hands between procedures
1876-1882 Robert Koch Koch's Postulates - determined a methodology for identifying pathogens, identified agents that caused Cholera, Tuberculosis. Germ Theory gains more acceptance
1885 Louis Pasteur Rabies Vaccine
1928 Alexander Fleming Discovered penicillin
1953 Jonas Salk Polio vaccine
1980 World Health Organization Declares smallpox eradicated
1983 Discover and Identification of AIDS virus (HIV)

Overview of Some Diseases (icky pictures)

Chart of Common Bacterial and Viral Diseases

The Germ Theory (around 1860)