Notes 11/30


November 30, 2009

Host-Pathogen Interactions

- Cannot grow viruses on a pure culture agar – MUST grow them in a host cell
- Cell Culture:
o If we need to grow a virus that ONLY infects humans – use cell culture
• Cells are placed in a flask or a dish
o Humans cancer cells are used because they divide indefinitely – whereas normal cells commit suicide after about 30 replications
o Still need to be provided with nutrients
• Cells are placed across the bottom
• Nutrient-rich fluid (similar to blood plasma) is them put in
o Common cultured cancer cells = HeLa cells
• Named from a person who died of her cervical cancer
• Henrietta Lacks infected with HPV-18
• HPV-18 destroys apoptosis (cell suicide) mechanism in epithelial cells → this made infected cells cancerous
o Cancer cells in general have large nuclei and are continually misshapen

Questions to Consider:
• How do pathogens and hosts influence each other’s evolution?
• How does ecology contribute to the ability of pathogens to cause disease?
• Do pathogens inevitably evolve to become less virulent to their hosts?
• Why do bacteria make ‘toxins’?
• What is the difference between a pathogen and normal flora

I. Terminology
a. Incidence vs. prevalence
i. Incidence
1. The number of new cases of a disease in a population divided by the total number of people in population
ii. Prevalence
1. Total number of cases of a disease divided by the total number of people in the population
b. Epidemic
i. Increase in incidence of a disease
c. Reservoir
i. Where the organism that causes the diseases habitually exists in nature
1. Ex. – HIV’s reservoir is in humans
2. Ex. – C. perfringen’s reservoir is soil
3. Ex. – V. fischeri’s reservoir is squid, seawater
ii. Microbes tend to become less virulent in their reservoir
d. Vector
i. Organism that transmits infectious diseases from host to host
1. Ex. Y. pestis (black plague) vector = flea
e. Virulent
i. Microbe that causes symptoms
f. Virulence
i. Ability to cause disease in a host
g. Virulence factor
i. Any chemical made by a pathogenic microbe that contributes to that microbe’s ability to cause symptoms

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