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Influenza C virus
Last reviewed: 08.07.2025
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The virion of the influenza C virus has the same shape as viruses of types A and B. However, it differs from them not only in antigenic properties, but also in a number of other features. The genome is represented by single-stranded negative RNA of 7 fragments, the nucleotide sequence of which differs significantly from those of viruses of types A and B.
The genome codes for 1-2 non-structural and 6 structural proteins. The type C virus lacks neuraminidase, so the outer membrane of the virion has only one type of spikes that are the same size as those of type A and B viruses (height 8-10 nm, diameter 4-5 nm), but located, unlike viruses A and B, not randomly, but with a clear hexagonal orientation at a distance of 7.5 nm from each other. The spikes are formed by the glycosylated peptide gp88, which has two functions: hemagglutinin and neuraminate-O-acetyl-esterase (glycopeptide HE). Accordingly, the type C virus is recognized by another cellular receptor - mucopeptide containing acetyl-9-0-acetylneuraminic acid. This circumstance determines the absence of competition at the adsorption stage between the type C virus and viruses of other types.
The influenza type C virus adapts to chicken embryos with much greater difficulty than the A and B viruses, and it reproduces both in chicken embryos and in cell cultures only at lower temperatures (32-33 °C). The type C virus is not as variable as the type A virus. Although the influenza C virus does not cause pandemics or large epidemics, it is often the cause of sporadic influenza diseases. The clinical picture of the disease is the same as in relatively moderate forms of influenza A. Diagnostics is based on the isolation of the virus in chicken embryos; the immunofluorescence method and other serological reactions are also used.
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