The Nature Of Disease

39.1 THE NATURE OF DISEASE

What is an infectious disease?  Infectious

disease: illness caused by the presence of a pathogen

 Pathogens:

disease causing organisms

Examples: bacteria, protozoa, fungi, viruses

• Pathogens are found in the soil, contaminated water, and infected animals (including humans)

Some microorganisms are beneficial  Some

microorganisms have a symbiotic relationship with our body Keep harmful bacteria from growing E. coli helps digest food

What causes a disease?  Genetic:

diseases are inherited

Example: hemophilia

 Aging:

wear & tear on the body

Example: osteoarthritis

 Exposure

to chemical or toxins

Example: cirrhosis

 Matnutrition: Example: scurvy

Koch’s postulates: relates a specific pathogen to a 1. Pathogen is found in the host in every case of the disease 2. Pathogen is isolated & grown in a pure culture 3. When pathogen is placed in healthy host it causes the disease 4. The pathogen is isolated from the new host & shown to be the original pathogen

Exceptions to Koch’s postulates  Some

bacteria has never been grown on an artificial medium  Viruses cannot be cultured

Transmission of disease 1. 2. 3. 4.

Direct contact By an object Through the air By an intermediate organism called a vector

Damage to host cells  Viruses

take over the host cell’s genetic and metabolic machinery & eventually cause the death of the cell  Bacteria release toxins that are transported by the blood and cause serious damage Destroy blood cells and blood vessels Produce fever Disrupt nervous system

Patterns of disease  Endemic

disease: a disease that is constantly present in a population (example the common cold)  Epidemic: many people in a given area are afflicted with the same disease at about the same time (example: influenza)

Treating disease  Antibiotic:

bacteria

a substance that treats a