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Lecture 8

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HIV populations evolve resistance toAZT within individual patients y-axis = survivorship (at low levels ofAZT, survivorship is fairly low and continues to drop) survivorship is higher because the pathogen has evolved a resistance toAZT that population of virus is evolving quickly in the patients due to drug treatment drug resistance as of function of the months of therapy Lecture 8 Virulence Evolution Explicit theory - write out in math and make inference from it 1918 Influenza epidemic (WW1) Confined spaces and highly populated living quarters led to easy dispersion of the virus The scale of the mortality (deaths per 100,000 per year) - the number of deaths is gradually decreasing due to the advances in medical care BUT there is a giant spike in mortality due to a single epidemic of the flu Why is it so virulent? Where did it come from? Where did it go? Influenza Ebola virus It appeared, made people really sick and then disappeared - then reappeared in monkeys, then again in Africa It appears, has a high kill rate and then disappears Why is the common cold so benign? Virulence There is a background mortality rate due to aging and extrinsic causes - virulence is additional mortality rate Conventional wisdom Using the host to replicate but if the host dies then it cannot continue replicating and transmitting - a virus that kills its host, kills itself The host might respond by decreasing susceptibility to the virulent factor and the pathogen will pay to decrease virulence to save the host so that it can continue to replicate and transmit to others Ebola virus Thought to circulate in bats - not very virulent Sometimes it can jump into an ape or chimp - who then spreads it to humans Since this is a new environment, it is highly virulent, so much so that it burns itself out SARS Thought to have crossed species and spread to humans, causing high mortality rates Origin of SARS Single strand RNAvirus Looked at RNAfor similarities to known RNAand pathogens Analysis suggests that Myxoma virus Highly virulent to rabbits - rabbits breed like crazy Scientists released a myxoma virus into the rabbit population to kill them and control the populati
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