Bird flu - Emerging Pulmonary Infections Tsunami lung, Bird...

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Emerging Pulmonary Infections Tsunami lung, Bird flu, SARS Dr. Zia Hashim
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Avian Influenza z Established as an epizootic z Will it be a long feared human pandemic
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Pandemics: Occur every 11-39 years z When new virus is introduced ± ± H1N1 H1N1 1918 Spanish flu: 20-40 million deaths ± ± H2N2 H2N2 1957 Asian flu ± ± H3N2 H3N2 1968 Hong Kong flu (H3N2: still circulates) All 3 pandemics spread world wide within 1 year
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Outbreak ¾ 1983: U.S. (H5N2) ¾ 1999-2000: Italy (H7N1) ¾ 1997: Hong Kong (H5N1) ¾ 2001: Hong Kong (H5N1) ¾ 2003: European (H7N7) ¾ 2003-2004: SE Asia 8 countries (H5N1) ¾ 2004-2005: SE Asia and Eurasia
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Indian scenario z Feb 18: India first case of H5N1 strain z 30,000 chickens died in Navapur z Jalgaon: 26 samples sent in February end to the High Security Animal Disease Laboratory (HSADL) in Bhopal z Tested positive: 4 z Poultry within 10 km from the affected villages culled: 73,000
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Influenza Viruses: Types Family: Orthomyxoviridae z Type A z Type B z Type C
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Type A z Multiple species { Humans { Avian Influenza z Most virulent group z Varying degrees of virulence, can infect humans, birds, pigs, horses
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Influenza A viruses Further divided into subtypes based on ¾ Hemagglutinin (H): 15 (H1 to H15) Function: Sites for attachment to infect host cells ¾ Neuraminidase (N): 9 (N1 to N9) Remove neuraminic acid from mucin and release from cell Possibility of unique 135 combinations
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Contents z Host-cell-derived envelope z Envelope glycoproteins: important for entry and egress from cells z Genome: RNA ¾ Segmented ¾ Negative-sense ¾ Single-stranded
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Type B z Mostly humans z Common z Less severe than A z Epidemics occur less often than A
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Type C z Humans and swine z Different pattern of surface proteins z Rare { Mild to no symptoms z By 15 years: most have antibodies
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“Antigenic Drift” z Type A: genetically labile z Don’t have good mechanisms for proofreading and repairing of errors that occur during replication z Genetic composition changes with replication in humans and animals z Minor changes called antigenetic drift
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“Antigenic Drift” Lack of effective proofreading by RNA polymerase High rate of transcription errors AA substitutions in surface glycoproteins Substitutions in Ag-Ab binding sites Evade humoral immunity Reinfection
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“Antigenic Shift”: new subtype z Swap genetic materials with other subtypes of influenza A including those of different species z Mixing vessel Mixing vessel ¾ Humans ¾ Pigs because both species can be infected with human influenza and avian influenza simultaneously
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“Antigenic Shift” If 2 influenza viruses simultaneously infect novel virus with new surface/internal proteins with new haemagglutinin subtype spreads efficiently in a naive human population Pandemic influenza viruses
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Antigenic Shift: Asia z Favorable conditions for antigenic shift are common in Asia z Humans: close proximity to ¾ Domestic poultry ¾ Pigs
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Why is H5N1 a concern? z
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This note was uploaded on 12/03/2011 for the course MEDICINE 350 taught by Professor Dr.aslam during the Winter '07 term at Medical College.

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Bird flu - Emerging Pulmonary Infections Tsunami lung, Bird...

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