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 disease Ex.: Type II diabetes, obesity in the U.S., TB in Russia Pandemic – an epidemic that has spread worldwide Ex.: AIDS, influenza in 1918 (killed 50 million!) Vector – animal, usually insect, that transmits an infectious disease Ex.: 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