December 8, 2008

1. Terminology
a. Incidence vs. prevalence:
b. Epidemic:
c. Reservoir (for infectious disease): where the organism causes a particular disease exists in nature
d. Vector: living organism that can transmit an infectious disease from host to host
e. Virulent: ability of microbe to cause disease in host
f. Virulence factor: any trait (expressed gene) that a microbe has that contributes to its ability to cause disease
g. Invasive disease: symptoms caused by microbe growing in normally sterile site
i. Invasion factor: any trait that contributes to microbe’s ability to cause an invasive disease
h. Toxigenic disease: symptoms caused by microbe in non-sterile site expressing protein (exotoxin) that’s toxic to us
2. Ewald’s hypothesis
a. In general, it is not in the interests of a pathogen to cause symptoms in a host
3. Examples of invasive bacterial diseases
a. Plague
i. Yersinia pestis- gram negative; grows in blood & lymph nodes. It is able to kill & then grow within immune cells.
ii. Virulence factors:
1. Y. Pestis makes a capsule
2. Produces a protein that induces apoptosis in immune cells
3. Hemagglutinin-clots blood; Sigma FactorOnly produced at 25 C
4. Plasminogen activator-dissolves blood clots; prevents immune cells from going to where the bad bacteria are; sigma factor only produced at 35 C
5. Fleas & rats- rats can have plague in their blood and then the fleas can bite the rat
a. Blood will clot in flea gutperpetual hunger for fleamore bites
b. For bacteria to spread, they must go throughout the blood of mammal host; ( should make protein to stop clotsspread thru bloodstream)
iii. Human history-pneumonic plague is person-to-person airborne spread; more deadly
b. Scarlet fever
i. Streptococcus pyogenes-gram positive cocci that forms chains
ii. Causes strep throat & scarlet fever
1. Spread from respiratory tract to the blood & leads to patchy rash, high fever, strawberry tongue, blindness, deafness, heart problems, death
iii. Virulence factors
1. Capsule
2. Proteins that lyse blood cells
3. A graph showing the number of scarlet fever deaths through 1840-1940 the number of cases declines because the bacteria simply stopped making the symptoms b/c they prevented the spread of bacteria that made the virulence factors

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