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29 Cards in this Set

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  • Back
What are the important clinical features of the influenza virus types A and B?
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
What are the structural characteristics of the influenza virus?
It has a helical nucleocapsid and lipid-envelope with viral glycoproteins
Describe the genome of the influenza virus
It is a segmented, single-stranded RNA virus with negative polarity
What are the two important glycoproteins on the influenza virus surface?
hemagglutinin (HA) and neuraminidase (NA)
Describe the hemagglutinin protein function
It contains a fusion peptide that is responsible for the fusion of the viral envelope with the cellular membrane following endocytosis
Describe the neuraminidase protein function
It permits the release of newly assembled virions by removing the sialic acid to which virions attach
What is antigenic drift?
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
What is antigenic shift?
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
What is the significance of antigenic shift in pigs coinfectced with human and avian virions?
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
What is the effect of anti HA antibodies?
They neutralize virions and block the sialic acid receptors
What is the effect of anti NA antibodies?
They inhibit the budding of new virions but do not block the initial attachement
What is required for the membrane fusion activity of HA to function and thus the infectivity of the virion?
Proteolytic cleavage of HA protein into disulfide bonded HA1-HA2 subunits
How does the proteolytic cleavage of HA occur?
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
What is the significance of the HA cleavage in the H5N1 strain?
It's HA is 100% cleaved by intracellular human endoproteases
What is the most important clinical type of infleunza?
Type A
How do pandemics of influenza occur and what type?
Influena A virus strains with new genome segments encoding new HA subtypes
What is the difference between type A and B in terms of antigenic variation?
Type B cannot undergo antigenic shift but can undergo genetic drift, although it is more gradual than type A
Describe the target populations for influenza vaccination
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)
Describe the components of the trivalent flue vaccine
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
What is meant by "split-virus" vaccine?
This is the subunit vaccine containing HA and NA envelope glycoproteins purified from the whole, inactivated virus (not recombinant)
Describe the indications for the whole-inactivated vaccine verses the purified subunit vaccine in terms of age
The whole-inactivated vaccine is indicated for those 12 and older, the purified subunit for those 6 months and older
Who can receive the new cold adapted intranasal vaccine?
Healthy people ages 2-49 years
What is the mechanism of action of amantadine and rimantidine?
They inhibit the influenza virion from uncoating
What is the method of action of the neuraminidase inhibitors and what are those drugs?
Zanamivir and oseltamivir inhibit the neuraminidase enzymes
When do anti-flu drugs need to be administered for effective therapy?
Within two days of initial symptoms
Which types of influenza A viruses have natural human to human transmission?
H 1-3
Why are pigs important in the transmission of the flu?
They contain receptors for many strains of human and avian flu and are a mixing pot for antigenic variation to occur
What assays are used to determine an influenza infection?
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
Whom is the infleuzna virus contraindicated?
Less than 6 mo and those allergic to chicken eggs