Influenza type C virus biology, interaction with the host, and epidemiology

Abstract

Influenza C virus is an enveloped RNA virus with seven single-stranded, negative-sensed RNA segments with 9 genes (Influenza types A and B viruses have 8 RNA segments with 10 genes). Influenza C virus RNA segments 1, 2, and 3 encode three basic protein polymerases, P1, P2, P3 respectively, which form a transcriptase that includes a capped RNA primer binding site, a nucleotide binding site, and a site for nucleotide chain elongation. Influenza virus RNA segment 4 codes for the one surface glycoprotein, HEF, which is responsible for attachment to the sialic acid host cell receptor, receptor destruction, and viral-cell fusion (similar to the HN glycoprotein of Paramyxoviruses). RNA segment 5 codes for the nucleoprotein (NP) which is the backbone of the helical nucleocapsid. Influenza C virus RNA segment 6 encodes mRNA which is spliced for translation of the matrix protein (M)(Influenza A and B viruses do not use spliced mRNA for the main M protein). The M protein functions in the assembly and budding of the virus. At present, the nonstructural proteins (NS1 and NS2) encoded by Influenza C virus RNA segment 7 have no known biological function. Replication and pathogenesis of Influenza C virus is similar to that of Influenza types A and B viruses, except Influenza C virus uses the 9-0-acetylated sialic acid receptor on the host cell, primary uncoating is slower, and secondary uncoating of the virus requires alkaline pH (similar to Paramyxoviruses).