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Lecture

Lecture 30: "Evolution & Human Health II"

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Department
Biology
Course Code
Biology 3466B
Professor
Yolanda Morbey

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Evolution Lecture No. 30: Evolution & Human Health II th Monday November 26 , 2012 Evolving Pathogens (Antibiotic Resistance): -Antibiotics like penicillin are chemicals that kill bacteria and act as agents of selection on bacterial populations Bacteria such as Pneumococcus may evolve resistance to antibiotics. An example is Pneumococcus bacteria in response to penicillin. From 1992 – 1995, the per capita consumption of penicillin dropped (high peak shown in graph). Pneumococcus is the most common cause of pneumonia. Evolving Pathogens (Virulence): -Virulence is the degree to which a pathogen negatively affects its host. Vertical transmission is where virulence affects reproduction within the host, while horizontal transmission is where virulence results in the infection of new hosts. The greater the virulence, the higher the lethality as observed in pathogens of high virulence like Cholera. Pathogens of minimal virulence like herpes and the cold virus produce symptoms alone. -The evolution of virulence has been proposed by three hypotheses: The coincidental evolution hypothesis (byproduct of selection in another environment, e.g. tetanus), the short-sighted evolution hypothesis (within host evolution, e.g. poliovirus) and the tradeoff hypothesis (virulence is a balance between benefits like horizontal and vertical transmission and costs like killing or debilitating the host). Of the three hypotheses, most pathogens are classified as evolving under the tradeoff hypothesis. The Polio virus is not very virulent, but escapes from the gut and into the nervous system (where it has a selective advantage and increases its reproduction). Virulence Evolution In A Bacteriophage: -In horizontal transmission, pathogens reproduce in a host cell and through secretion, spread to different cells to repeat the process (infection via secretion). In vertical transmission, pathogens reproduce in a host cell and through cell division, multiply their impact upon the host (infection via cell division). Virulence can evolve very quickly in experimental populations. In a graph of infected E. Coli hosts, the red dots represent horizontal transmission being more important to pathogens, while the blue do
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