influenza and other enveloped viruses Flashcards
characteristics of enveloped viruses
1: a nucleocapsid coated with a lipoprotein membrane
2: infectivity destroyed by treatment with ether
3: unstable so transmission requires close contact
4: more complicated pattern of assembly than that on nonenveloped
5: few cell-associated virions at any time
6: continuous release of virions without gross cellular damage
7: modified cellular membrane containing glycoproteins within the envelope membrane
8: released from infected cells by budding
9: antigens for neutralizing antibody are envelope glycoproteins
envelope
What are the features of viral envelopes… What are they composed of?
Can enveloped viruses be neutralized?
Are they sensitive to ether?
Are they stable?
Are infected cells killed? How does the virus leave the cell?
composed of lipid molecules and viral glycoprotein spikes
neuraminidase and hemagglutinin
antibodies can’t neutralize because can’t get to capsid - target antigens are on envelope
makes viruses sensitive to ether - can’t bind to cells anymore because will dissolve the envelope
enveloped viruses usually unstable extracelluarly
virus doesn’t have to kill cell to get out of it - just buds out
classes of enveloped viruses
paramyxo- herpes- toga- flavi- rhabdo- orthomyxo- hepadna- retro- pox-
budding of enveloped viruses
viral caspid attaches to transmembrane receptors on host plasma membrane - these receptors were made using viral genetic material
this membrane surrounds the viral caspid and buds off
orthomyxoviruses genetic material
aka influenza virus A, B, C
What is the structure of nucleotide?
Plus or minus strand?
contain 8 separate segments of single-stranded RNA - each segment has the genetic information to encode at least one unique viral protein
each RNA segment enclosed in separate helical nucleocapsid
RNA cannot function as mRNA because is minus strand
virion contains virus-specific RNA polymerase - makes mRNA from virion (-)-stranded RNA
replication cycle of influenza virus
1: attaches to cell membrane
2: endocytosis and acidification
3: fuses with endosome/lysosome membrane and releases genetic material into cell
4: genetic material moves to nucleus
5: converted to mRNA and translated
6: translated proteins move back to nucleus and others are post-translationally processed and inserted into the host cell plasma membrane
7: genetic material is moved from nucleus to cytoplasm and packaged in host cell membrane where the viral proteins have been inserted
buds off and is released
classes of viral antigens (2)
1: nucelocapsid proteins
2: envelope glycoproteins
nucleocaspid
How many nucleocapsids do orthomyxoviruses aka flu virus have?
Do antibodies to nucleocapsids have effect in enveloped viruses?
structure composed of caspid proteins and nucleic acid genome
antigens located on protein capsomers of helical nucleocapsids inside virion
orthomyxoviruses have eight separate helical nucleocapsids
antibodies to nucelocaspid proteins don’t neutralize virions because don’t penetrate past the envelope around the virions
caspid proteins
What are?
protein coat that covers the nucleic acid genome
envelope glycoproteins
What are the two envelope glycoproteins that are antigens?
hemagglutinin and the enzyme neuraminidase
hemagglutinin (H or HA)
What does this glycoprotein do for the virus?
How effective are antibodies to this envelope protein?
required for adsorption of virions to cells - required for infection of susceptible cells
antibodies directed against it will neutralize orthomyxovirus virion - these antibodies are most important in controlling infection
binds to sialic acid molecules on host cells
neuraminidase (N)
What does this enzyme do for the virus?
enzyme that releases newly formed virions from their final point of attachment to the infected host cell by cutting sialic acid bonds
antibody to it slows release of newly formed virions and spread of infection to other individuals, reduces severity of disease but does not block infection of new cells or neutralize virions
hemagglutination
What is?
What virus is this diagnostic for?
Does agglutination test for the whole virion?
process by which orthomyxoviruses agglutinate red cells
used to measure relative concentration of virions in a clinical sample
does not require that the virions be infectious - only that H-antigen present
since specific antiviral antibody directed against H-antigen inhibits hemagglutination can be used to titrate the relative concentration of antiviral antibodies in serum samples - if antibody present won’t get glutination - RBCs will clump
when virus present, RBCs won’t form clump at bottom of test tube - form sheet so still clump, but it looks clearish/light pink and is spread out
influenza epidemics
What is the definition of an epidemic?
pandemic (world-wide epidemic) of 1918-1919 caused millions of deaths (30-50 million)
epidemic detected/determined by calculation of how many people die over what’s expected for that disease
types of influenza virus
three types: A, B, and C
each has its own specific nucleocapsid antigen (one for A, B, and C - called the S-antigen)
multiple strains of each type based on antigenic differences in hemagglutinin and neuraminidase and genetic variation in polymerase genes and other genes
influenza type B epidemics
How often do these occur?
What do the vaccines include?
occur every 3-6 years
vaccine usually contains one B strain that’s anticipated to represent the predominant H-antigen and N-antigen types for the future flu season
killed flu vaccine contents
Why are killed flu vaccines suboptimal?
vaccine usually contains one B strain and two A strains that are anticipated to represent the predominant H-antigen and N-antigen types for the future flu season
influenza type C has minor clinical significance
formaldehyde killed
injected
new virus isolates added each year
more than 70% effective when vaccine is well-matched to predominant viruses
suboptimal in protection because does not efficiently induce secreted IgA - primarily induces IgG response and IgG antibodies
recommended for everyone over the age of 6 months, special risk groups, and medical personnel
about 65% effective - but likely to be less severe illness if vaccinated even if you do get sick
live flu vaccine contents
What are the benefits?
What age groups are recommended?
approved in 2012
has two influenza A and two B strains or several of each
administered by intra-nasal spray
selected for optimal growth at low temperature - so ideal for upper respiratory tract and nasal cavity but does’t grow well deeper in the respiratory tract
approved for use in ages 2-49
may give 30-50% greater efficacy than killed (at least in preschool-age children)
get more IgA response with this than with the killed vaccine