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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
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