Genus Influenzavirus C

Type Species	Influenza C virus	(FLUCV)

Distinguishing Features

Member viruses of the genus Influenzavirus C naturally infect humans. Viruses have 7 genome segments. They lack neuraminidase. The hemagglutinin (HEF) protein also has the function of a fusion protein and of a receptor-destroying enzyme which is a 9-0-acetylneuraminyl esterase. The conserved end sequences of the viral RNAs of the influenzaviruses C are 5-AGCAGUAGCAA . . . , and 3-UCGU(U/C)UUCGUCC . . . RNA segments 1-3 encode the P proteins (Mr 87.8 10³, 86.0 10³, 81.9 10³). Segment 4 encodes HEF (unglycosylated: Mr 72.1 10³ ), segment 5 NP (Mr 63.5 10³), segment 6 M and CM₂ (Mr 27.0 10³ and 18.0 10³) and segment 7 NS₁ (Mr 27.7 10³) and NS₂ (Mr 21.0 10³).

Antigenic Properties

Antigenic drift characterized by the emergence of successive antigenic variants which have descended from those that circulated previously apparently does not occur among influenzaviruses C; however, antigenic variation between distinct co-circulating lineages has been detected in HI tests with both anti-HEF Mabs and polyclonal antisera. Viruses exhibit no cross-reactivity with influenzaviruses A and B, although homologies of HEF to influenzavirus A and B HA were identified near the amino and carboxy termini and several of the cysteines co-aligned in the sequences. Antibody to HEF neutralizes infectivity.

Biological Properties

Infection in humans is common in childhood. Occasional outbreaks, but not epidemics, have been detected. Swine in China have been reported to be infected by viruses similar to human Influenza C virus strains.

List of Species Demarcation Criteria in the Genus

No separate species are currently recognized in the genus Influenzavirus C. This genus is comprised of a cluster of strains that replicate as a continuous lineage and can reassort genetically with each other. Although detectable antigenic and sequence differences exist among this genus, these differences are not sufficient for separate species designation.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus name, genome sequence accession numbers [ ], and assigned abbreviation ( ) are:

Species in the Genus

Influenza C virus C/California/78	[K01689, M10087, M17700]	(FLUCV)

Tentative Species in the Genus

None reported.