L20 - influenza Flashcards
what is in influenza
segmented , negative sense single-stranded RNA virus
symptoms of the flu
headache , fever , cough , sore throat and muscles
- maany people feel incredibly tired and aching can be severe
= life threatening to immunocomprimised people
how many deaths by the ‘normal’ flu are there a year
10,000
= rarely the flu that does final blow = damages the immune system
= another infection kills you
charecteristics of influenza A
enveloped virus
negative sense RNA genome with 8 segments
each segment 1000-2500 nucleotides long
6/8 segments code for single virus - 2/8 each code 2 each
= 10 total ‘classical’ proteins
influenza structure
coated by Lipid bilayer envelope
embedded with glycoproteins:
- Heamagglutanin
- Neuraminidase
M2 ion channel to allow protons in for acidification and uncoating
M1 matrix that provides stuctural support and links envelope to RNP core
RNP core - 8 gene sgments bound by NPs
= nucleoproteins
what does negative sense mean
cannot be directly translated at ribsosomes
must first serve as template to produce ‘positove sense’ RNA
= can be translated
attachment and delivery of incluemza to nucleus
- virus binds to sialic acid residues via haemagglutanin
- endocytosis
- endosome is acidified by H+ ions through M2 channel
- M1 discociates from RNPs freeing the genome segments
- gene segments transported to nucleus due to NLS - (Nuclear localsiation signal)
what is the ssRNA in influenza always wrapped in
Nucleocapsid protein
= acociates with RNA polymerases
what must be made in replication of negative sense Influenza virus in host nucleus
progeny (negative sense) genome
= the genetic information of the virus
antigenomes (positive sense)
= +sense mRNA can be translated at ribosomes to make viral proteins
what is the main attachment protein of influenza and what does it bind to
Heamagglutinin
= binds sialic acid resudyes on surface proteins
what are serotypes in flu
distinct variations in genes
= in flu the main serotypes occor from H and N glycoprotein variations
what is antigenic drift
replication of genome segments can make errors
mistakes in new viral genome are different to their parent genome
= altered proteins = different H and N glcyoproteins on surface
what are the consequnces in terms of infection when talking about antigenic shift
infection with strain A may produce antibodies specific to A
A can undergo ntigenic shift alterring its surafce ptoteins to become strain B
if later infected by strain B you are less protected as your antiboies only recognise part of the new strain
= mild infection = protected to lesser degree
why is antigenic shift particular annoying in the influenza virus
Haemoglutanin is very tolerable to changes
= still functional
= reduces effectiveness of vaccines as antigenic shift is continous
= viruses becoming more and more different to orginal vaccine strain
what are pigs considerred in terms of influenza
mixing pots
pigs infcted with 2 strains of virus can produce new strains
= 8 segments recombine with the other 8 gene segments
= antigenic SHIFT
shift is the big one drift is the small
why is gene reassortment withing pig ‘mixing pots’ available to flu virus
H and N genes are on seperate gene segments
= reassoted genomes can be more infectious
when 2 strains of virus infect cell –> when new viraklparticles are being made –> segments from each can combine
= new strain
= antigenic shift
2 other ideas for new strain production in flu virus
- particular stain evolves and adapts to a new host
- 2 different stains infect same host/human and there is genomic reassortment
