Influenza B
Influenza viruses belong to the family Orthomyxoviridae. The viral particles are about 80-120 nm in diameter and can be spherical or pleomorphic. Their lipid membrane envelope contains two glycoproteins: hemagglutinin (HA) and neuraminidase (NA). These two proteins determine the subtypes of Influenza A virus. There are 16 H subtypes and 9 N subtypes known, but only H1, H2, H3, and N1, N2 are commonly found in humans.
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HA is the major surface antigen of the influenza viruses, against which neutralizing antibodies are elicited during virus infection and vaccination. The single polypeptide HA is subsequently cleaved into two polypeptides, HA1 and HA2. The HA1 polypeptide mutates more frequently than HA2, and plays a crucial role in natural selection.
The Influenza A viral genome consists of eight, single negative-strand RNAs that can range between 890 and 2340 nucleotides long, encoding for 11 proteins: hemagglutinin (HA), neuraminidase (NA), nucleoprotein (NP), M1, M2, NS1, NS2 (nuclear export protein), PA, PB1 (polymerase basic 1), PB1-F2 and PB2.
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