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29 Cards in this Set
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- Back
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What are the important clinical features of the influenza virus types A and B?
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They show a rapid onset of symptoms following a two day incubation period, headache, fever, chills, generalized aches, sore throat with dry and non productive cough
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What are the structural characteristics of the influenza virus?
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It has a helical nucleocapsid and lipid-envelope with viral glycoproteins
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Describe the genome of the influenza virus
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It is a segmented, single-stranded RNA virus with negative polarity
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What are the two important glycoproteins on the influenza virus surface?
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hemagglutinin (HA) and neuraminidase (NA)
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Describe the hemagglutinin protein function
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It contains a fusion peptide that is responsible for the fusion of the viral envelope with the cellular membrane following endocytosis
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Describe the neuraminidase protein function
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It permits the release of newly assembled virions by removing the sialic acid to which virions attach
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What is antigenic drift?
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Gradual change in antigenicity of either the HA or NA proteins which is due to genetic point mutations; occurs in type A and B viruses
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What is antigenic shift?
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Major antigenic change in the HA and NA that occurs by genetic reassortment of the genome segments in cells infected with two strains; only occurs in type A viruses
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What is the significance of antigenic shift in pigs coinfectced with human and avian virions?
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The avian virus and the human virus could potentially genetically reassort, generating antigenic shift which would give an extremely virulent avian virus that could infect humans
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What is the effect of anti HA antibodies?
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They neutralize virions and block the sialic acid receptors
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What is the effect of anti NA antibodies?
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They inhibit the budding of new virions but do not block the initial attachement
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What is required for the membrane fusion activity of HA to function and thus the infectivity of the virion?
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Proteolytic cleavage of HA protein into disulfide bonded HA1-HA2 subunits
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How does the proteolytic cleavage of HA occur?
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Low levels of proteases such as "tryptase Clara" which is secreted by Clara cells into the respiratory secretions, or proteases produced by bacteria in the respiratory tract
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What is the significance of the HA cleavage in the H5N1 strain?
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It's HA is 100% cleaved by intracellular human endoproteases
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What is the most important clinical type of infleunza?
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Type A
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How do pandemics of influenza occur and what type?
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Influena A virus strains with new genome segments encoding new HA subtypes
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What is the difference between type A and B in terms of antigenic variation?
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Type B cannot undergo antigenic shift but can undergo genetic drift, although it is more gradual than type A
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Describe the target populations for influenza vaccination
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Persons who are at increased risks for complications including adults over 65, children 6mo-18y, and persons who can transmit flu to those at high risk (healthcare workers, care givers, parents)
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Describe the components of the trivalent flue vaccine
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The vaccine is inactivated and contains antigenic components of type A H3N2 and H1N1, and type B determined to be the most predominant for that upcoming season
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What is meant by "split-virus" vaccine?
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This is the subunit vaccine containing HA and NA envelope glycoproteins purified from the whole, inactivated virus (not recombinant)
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Describe the indications for the whole-inactivated vaccine verses the purified subunit vaccine in terms of age
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The whole-inactivated vaccine is indicated for those 12 and older, the purified subunit for those 6 months and older
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Who can receive the new cold adapted intranasal vaccine?
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Healthy people ages 2-49 years
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What is the mechanism of action of amantadine and rimantidine?
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They inhibit the influenza virion from uncoating
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What is the method of action of the neuraminidase inhibitors and what are those drugs?
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Zanamivir and oseltamivir inhibit the neuraminidase enzymes
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When do anti-flu drugs need to be administered for effective therapy?
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Within two days of initial symptoms
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Which types of influenza A viruses have natural human to human transmission?
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H 1-3
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Why are pigs important in the transmission of the flu?
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They contain receptors for many strains of human and avian flu and are a mixing pot for antigenic variation to occur
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What assays are used to determine an influenza infection?
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Nucleic acid specific assays in determining between A and B; antigen capture ELISA and neuraminidase assays are useful for prescribing therapy but can't determine type
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Whom is the infleuzna virus contraindicated?
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Less than 6 mo and those allergic to chicken eggs
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