Notes on Genus: Influenzavirus C

enveloped spheres or pleomorphic
enveloped spheres or pleomorphic

Type member: Influenza C virus


General Description

The genus Influenzavirus C is one of the genera in the family Orthomyxoviridae. It is named from the type (and only) member (derived from the latin influentia = epidemic). It differs from the other influenzaviruses in having 7 rather than 8 genome segments and in encoding a hemagglutinin with esterase activity on segment 4.


Virions spherical or pleomorphic, enveloped, 80-120 nm in diameter, with projections 4-6 nm in diameter and 10-14 nm long.


Single-stranded negative sense RNA in 7 segments totalling about 12.9 kb. The segments do not have a genome-linked protein (VPg) at their 5'-terminus nor a 3'-polyA tail.

Genus Genomic Organization

There are 7 RNA segments. The larger genome segments each encode a single protein while the smaller segments often encode additional proteins from spliced or bicistronic mRNAs.

Type Member Genomic Organization

There are 7 RNA segments:
  • RNA1 (2365 nts) encodes a basic polymerase (PB2) of 87.8 kDa
  • RNA2 (2363 nts) encodes a basic polymerase (PB1) of 86.0 kDa
  • RNA3 (2183 nts) encodes an acid polymerase (PA) of 81.9 kDa
  • RNA4 (2071 nts) encodes a hemagglutinin esterase (HE) of 72.1 kDa
  • RNA5 (1797 nts) encodes the coat protein (Nucleoprotein, NP) of 63.6 kDa
  • RNA6 (1180 nts) encodes two matrix proteins (M1 and M2) of 27.1 and 15.5 kDa
  • RNA7 (934 nts) encodes a non-structural protein of 32.5 kDa