The more you know…

Diseases

Diseases can disrupt homeostasis (balance) Diseases can have many causes:

Ex.: genetic, congenital (embryonic development), environmental, emotional/psychological, etc.

Infectious diseases are caused by pathogens and may be transmitted (contagious/communicable)

Pathogens = germs and other disease-causing agents: Ex.: Bacteria, viruses, parasites (protists, worms), prions

Germ Theory of Disease (1800s) States that some

microorganisms cause diseases

Important contributors: Louis Pasteur – first to grow

microbes from air in nutrient solution; vaccination (rabies, others); pasteurization (sterilization of milk, etc.)

Robert Koch – created the steps to prove that a microbe causes a disease (Koch’s postulates)

Koch’s Postulates – R. Koch demonstrated that anthrax bacteria cause disease in cattle and developed these rules:

Pathogens

How do pathogens cause disease?Disrupting the normal functioning of

the host’s cells:

Producing toxins (poisons) Destroying cells and tissues “Stealing” resources from body cells

How do contagious (communicable) diseases spread? indirect contact w/ infected person

- air, objects, substances direct contact w/ infected person

(touch) Water and food (contaminated) Animal bites – animal is the vector

*Many diseases spread through body fluids*

Disease Transmission

Vectors

Indirect contact through air

Indirect contact by objects

Direct contact

Disease Transmission Terms Epidemiology – study of how diseases spread in a population Outbreak – an unusual number of cases of a disease Endemic – a disease that always exists in a given area

Ex.: malaria in tropical Africa, common cold in U.S. Epidemic - a relatively large and increasing number of cases of a

diseaseEx.: Type II diabetes, obesity in the U.S., TB in Russia

Pandemic – an epidemic that has spread worldwideEx.: AIDS, influenza in 1918 (killed 50 million!)

Vector – animal, usually insect, that transmits an infectious diseaseEx.: mosquito that transmits malaria or yellow fever

Reservoir – animal, human, inanimate (water, soil) that serves as a source of pathogens

How small is a germ?Size Comparison:Pathogens & Human Cells

http://www.cellsalive.com/howbig.htm

http://www.unitedstreaming.com/index.cfm?media_file_id=1000667