Influenza Flashcards
What is influenza and what are its symptoms?
Specific respiratory syndrome caused by influenza virus
Symptoms:
- fever/chills, cough, headache, muscle aches, fatigue, loss of appetite
- normal CXR
- acute infection lasting about 7 days or longer, no persistence of virus, weakness and cough may last for several weeks
What groups are at risk for death/severe complications?
The young, elderly, and those with underlying chronic heart, lung, renal or metabolic conditions
How is the virus spread?
Droplet infection from coughing/sneezing
- incubation period 1-5 days, infectious for 5-6 days
What is the pathogenesis of seasonal influenza?
- Droplets enter respiratory tract
- Virus binds to sialic acid-containing receptors on non-ciliated respiratory epithelium
- replicates in epithelial cells of RT
- tissue damage and inflamm response –> cytokines and IFN –> fever, malaise, head and muscular aches
- pre-existing and developing immunity clear virus
- later in infection - possibility of secondary bacterial infection
What sort of virus is the influenza virus?
Enveloped virus with a segmented genome of ss-RNA of -ve sense
- 3 types, A,B,C (A & B in humans)
What is hemagglutinin?
- Trimer of 3 identical molecules
- grips the sialic acid
What is neuraminidase?
- Tetramer of 4 identical subunits
- sialic acid binds on each of the monomers and the NA will cut it off
What are the current circulating viruses in humans?
H1N1 and H3N2
What is the replication cycle of influenza?
- HA binds
- Receptor mediated endocytosis
- endosome becomes acidic, viral RNPs escape
- viral RNA rep & mRNA synth
- HA,NA expressed on cell surface after glycosylation in ER and golgi
- viruses bud out of cell
- SA snips off sialic acid in area of budding
- virus activated by action of tryptase Clara
What are the adaptive immune responses to influenza virus infection?
CD 8+ Cytotoxic T cells
- kill virus infected cells
- broadly crossreactive between A subtypes
Antibody
- developing antibody to HA speeds clearance
- inhibits attachment, release, helps lysis of cells and promotes phagocytosis
- only protects against the one subtype but lifelong response
What is antigenic drift?
- Mutation and selection
- often in the AB binding site
What is the influenza vaccine?
- Inactivated trivalent vaccine containing 3 different influenza viruses
- given intramuscuarly
What is the influenza vaccine?
- Inactivated trivalent vaccine containing 3 different influenza viruses
- given intramuscularly
What are some other targets of antiviral drugs?
- Ion channel blockers (prevent the endosome escape of RNPs)
- NA inhibitors (block efficient release)
What is antigenic shift?
Sudden appearance of an influenza A virus or a new HA within the human population
- complete lack of protective immunity –> pandemic
