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University of Toronto St. George
Molecular Genetics and Microbiology
Alan Cochrane

MGY378Microbiology II Virology Lecture 1 IntroductionViruses1 Multiply only in living cells 2 Are obligate parasites are metabolically inert outside the host 3 Rely on host metabolic processes for reproductionViruses exist for all known life forms Viruses are of interest to a Understand the basis of disease in humans domestic animals and plants and to develop cures b Experimental tools for molecular cell biology c As vectors for the introduction of foreign DNA into cells for the correction of genetic mutations adding genes disease treatment etc The average healthy individual harbours between 812 different mammalian virsuses at any one timeThe concept of VIROMICS ie viral genomics is becoming more pervasive in the study of virologyIt can vary based on geographic location but there are many persistent viral infections to human beings as a speciesNEW viral pathogens emerge as we are constantly exposed to new pathogens and viruses as the environment changesOver time disease distribution can fundamentally change a ie the distribution of DENGUE FEVER diminished from the 30s to the 70s due to the use of DDT resulting in widespread death of the disease vectorthe mosquito b However once DDT use was stopped Dengue fever rose again toward the 90s FACTORS AFFECTING NEW VIRUS EMERGENCE AND TRANSMISSION 1 High population density p2p transmission 2 Rapidtransit between continents ie SARS swine flu 3 Encroachment of humans into new environments exposed to new pathogens 4 Global warming expansion of areas that can support disease vectors 5 Changes in social normsmore sexual partners tattoos and piercings and IV drug use Steps in the emergence of hostswitching viruses 1 ExposureInfectionSpreadAdaptation FITNESS VALLEY A blockade to viral survivorship to prevent infection from one individual to anotherThe shallower the fitness valley the easier the transmission of virus from donor to recipientIn the emergence of host switching viruses into a new host there will be little or no transmission 1 An occassional virus gains the ability to spread in the new host and emerge as a potential epidemic depending on transmission conditionsThe terminating white circles in the diagram represent the extinction of the viral strain and the propogating filled circles represent the evolved strain VARIATIONS IN VIRUS COMPLEXITY1 SIMPLEST VIRUSES
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