Virology 3 Flashcards
Baltimore Classification of Influenza?
Group 5: negative sense RNA
Influenza belongs to what family?
Orthomyxoviridae
-Influenza is the only genus that belongs to this family
Influenza can be divided into 3 types:
-Influenza A
-Influenza B
-Influenza C
Influenza A:
-Can infect multiple species
-Most virulent
-Most important human pathogen
-Can further be defined based on serotypes
Influenza B:
-Only infects humans and seals
-Less genetically diverse than influenza A
-1 serotype
-We obtain immunity to this strain at an early age
Influenza C:
-Can infect multiple species
-Causes severe illness and local epidemic
What are serotypes?
A subdivision of viruses based on antigenicity
Influenza A can further be divided on serotypes:
-Divided based on two surface proteins
H:hemagglutinin (1-15)
N:neuraminidase (1-9) e.g H5N1
Examples of hosts Influenza A effects:
-Birds
-Swine (pigs)
-Humans
-Horses
-Ferrerts, Mink
-Seals, whales
Structure of influenza:
-100nm
-Spherical or filamentous (pleomorphic)
-Segmented genome
-Helical capsid
-Lipid envelope
Components of influenza:
-11 proteins (HA and NA being the major ones)
-10 genes with overlapping reading frames
-Replicates in the nucleus
-RNA polymerase (PA, PB1/2)
-Nucleocapsid (NP)
-Non-structural proteins (NS1, NS2)
-Matrix proteins 1&2
Major proteins in influenza
- NA
-HA
*These proteins are targeted by antiviral drugs
Neuraminidase (NA) 1-9:
-Glycoprotein found on the outside of the viral particle
-Enzymes is involved in the release of the viral particles from the cell
Haemagglutinin (HA) 1-15:
-Lectin protein that mediates binding and entry of the virus to target cells
Influenza Genome organisation:
-8 segmented single stranded negative RNA genome
-Has no nucleic acid proof reading
Influenza replication cycle: steps 1
- Virus binds via HA to sialic acid receptors on susceptible cells and enters via endocytosis or Viropexis.
Influenza replication cycle: steps 2
- Virus nucleocapsid containing the negative viral RNA is transported to the nucleus
Influenza replication cycle: steps 3
- VRNA is transcribed to complementary viral +mRNA via VRNA polymerase
Influenza replication cycle: steps 4
- Viral complementary positive mRNA is either exported to cytosplasm and golgi/ER and translated or remains in the nucleus
Influenza replication cycle: steps 5:
- The viral proteins return to nucleus and induce new negative viral RNA and nucleocapsid
Influenza replication cycle: steps 6, 7, 8
- HA and NA proteins migrate to plasma membrane
- Matrix and NS2 shutoff replication deliver nucleocapsid to plasma membrane
- Virus assembles and buds from cell and the host cell dies
The synthesis of mRNA in influenza is catalysed by what enzymes?
-Viral RNA- dependent RNA polymerase
What are two forms of positive sense RNA:
-Viral mRNA
-cRNA (complementary RNA)
Difference between viral mRNAs and cRNAs?
-mRNA are capped and polyadenylated
-cRNA is not capped or polyadenylated
*Both molecules contain a 5’ triphosphate group
Two mechanisms of antigenic variation (how variations arise:
-Antigenic drift: minor changes in antigen structure
-Antigenic shift: major changes in antigen composition (occurs after viruses with segmented genomes co-infect and exchange components)
