Influenza C

Influenzavirus C is a genus in the virus family Orthomyxoviridae, which includes those viruses which cause influenza. The only species in this genus is called "Influenza C virus".

Influenza C viruses are known to infect humans and pigs, giving them influenza. Flu due to the type C species is rare compared to types A or B, but can be severe and can cause local epidemics.

Types A and B have 8 RNA segments and encode 11 proteins. Subtype C has 7 RNA segments and encodes 9 proteins.

Enveloped. Usually rounded but can be filamentous. The virions are 80-120 nm in diameter.

GENE EXPRESSION

Viral RNA polymerase (PB1, PB2 and PA) transcribes one mRNA from each genome segment. Transcription is primed by cap cleaved from cellular mRNAS by Cap snatching. mRNA are polyadenylated by the viral polymerase stuttering on a poly U track. NS mRNA can be spliced, giving rise to mRNA coding NEP protein. Polyprotein p42 is cleaved in M1 and CM2 proteins.

REPLICATION

NUCLEUS

Virus attaches to sialic acid receptor though HEF protein and is endocytosed in the host cell.

Endosome acidification induces fusion of virus membrane with the vesicle membrane; encapsidated RNA segments migrate to the nucleus.

Transcription of genomic segments by the viral polymerase produces mRNAs.

Genomic (-)RNA is replicated through antigenomic (+)RNA intermediate.

High level of M1 protein induces genomes segments export from nucleus by NEP protein.

Virus assembly and budding occurs at the plasma membrane.