chapter_12 - Part V: The Immune System in Health and...

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Chapter 12 Failure of Host Defense Mechanisms Part V: The Immune System in Health and Disease 1. Pathogen avoids the immune system [Pathogens avoid the immune system long enough to infect another person. Killing the host (or killing him too soon) is usually disadvantageous to the pathogen.] Host invents defenses Pathogen and host co-evolve, neither eradicating the other (usually) 2. Immunodeficiency Inherited acquired (e.g., HIV/AIDS) pathogen invents strategies to avoid the defenses
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~84 Streptococcus pneumoniae serotypes 1. A variety of serotypes (antigenic types) simultaneously in the environment Similar for the virus that causes common cold Explains why a vaccine for these diseases is difficult. (A 23- valent capsular S. pneumoniae polysaccharide vaccine is available.) Explains why younger people get more colds than older people. Therefore, each infection with a different serotype is like a new disease Antigenic Variation (three types) Figure 12.1 7 th ed
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2. Changes by mutation or gene exchange: antigenic drift and antigenic shift Antigenic Variation (three types) The problem for the influenza virus is that it rapidly infects many people. Since immunity protects from reinfection, virus will quickly run out of hosts to infect. The solution is to mutate such that new antigens are presented each year. Antigenic drift leaves some epitopes from previous strain. Thus, previous exposure (immunity) to related stains may mitigate the severity of the disease and the symptoms but still lets the virus replicate and spread. 2. Changes by mutation or gene exchange: (a) antigenic drift and (b) antigenic shift
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Antigenic shift can create viruses that do not share epitopes with previous strains (no cross-reaction). Therefore, there is no partial protection from previous infections and the disease is much more severe than in years where there is only antigenic drift . Antigenic Variation (three types) 2. Changes by mutation or gene exchange : antigenic drift and antigenic shift The flu pandemic of 1918-19 killed >40,000,000. Was the worst pandemic of the last century. Also, antigenic shifts in 1957, 1968, 2009 (current swine flu) On average, how many Americans die of influenza every year? Answer: >35,000 Human influenza virus Swine influenza virus
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Center for Disease Control (CDC) http://www.cdc.gov/flu/avian/outbreaks/current.htm Avian Influenza: Current Situation (October 27, 2008) PDF formatted for print (195 KB/3 pages) Assessment of Current Situation (shown below) Human H5N1 Cases Animal H5N1 Cases Bird Import Ban Travel CDC Response Assessment of Current Situation The highly pathogenic avian influenza A (H5N1) epizootic (animal outbreak) in Asia, Europe, the Near East, and Africa is not expected to diminish significantly in the short term. It is likely that H5N1 virus infections among domestic poultry have become endemic in certain areas and that sporadic human infections resulting from direct contact with infected poultry and/or wild birds will continue to occur. So
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This note was uploaded on 09/22/2011 for the course BIOL 6570 taught by Professor Jenniferleavey during the Spring '11 term at Georgia Institute of Technology.

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chapter_12 - Part V: The Immune System in Health and...

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