december 2,2009 notes

December 2, 2009—notes
Terminology:
1. Incidence of disease: the number of new cases of a disease in a population / total number people in population
2. Prevalence: total # of cases of disease/ total # of ppl in population
3. Epidemic: increase in the incidence of a disease (increase in the number of new cases of a disease)
4. Reservoir : where the organism causing a disease habitually exists in nature
a. Ex. HIV’s reservoir is humans
b. C. perfringens reservoir is soil
c. V. fischeri reservoir is squid, seawater
Over time, most microbes become less virulent in their reservoir
5. Vector: Organism that transmits infectious disease from host to host
a. Ex. Black plague is caused by Y. pestis – vector is the flea
6. Virulent Microbe that causes symptoms
a. Virulence: ability to cause symptoms
7. Virulence factor: any protein that is produced by a pathogenic microbe that contributes to the microbes ability to cause symptoms
8. Invasive disease: infectious disease where symptoms because of microbes growing in what, in a healthy host, is a sterile site
a. Invasion factors: chemicals produced by pathogens ( microbes that cause disease) that allow those pathogens to get into normally sterile tissues
9. Toxigenic disease: microbes growing in normally not-sterile site, producing “toxin” that leads to symptoms in host. Example: toxic shock syndrome& S. aureus makes TSST-1
a. Exotoxin: protein expressed by actively-growing bacteria, which leads to symptoms in the host
b. Endotoxin= Lipid A of LPS
b) Two examples of toxigenic bacterial diseases
1. Botulism
a. Clostridium botulinum: like other clostridia sp.,
• Strict anaerobes
• Spore-forming
 Spores: very durable, suspended-animation state of bacteria
• Reservoir: soil
b. Botulism toxin: deadly dose: 1ng/kg weight of person
• Death from suffocation BoTox disables motor neurons, including those that control diaphragm which leads to not being able to breath
c. Botulism food poisoning: anaerobic environment created by canning causes germination of C. botulinum spores which leads to expression of botox gene, which leads to botox in jar
d. Infant botulism and normal flora:
• Human gut is non-sterile, anaerobic
• C. botulinum spores in soil, elsewhere
• Gut a good place for C. botulinum to grow- except that, in a healthy adult, normal flora filled spots for C. botulinum to grow
• In infants, little normal flora to displace C. botulinum bacteria, which leads to “ Floppy baby syndrome”

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