Influenza C virus is the species in the genus Gammainfluenzavirus, in the virus family Orthomyxoviridae, which like other influenza viruses, causes influenza.
Flu due to the Type C species is rare compared to Types B or A, but can be severe and can cause local epidemics. Type C has 7 RNA segments and encodes 9 proteins, while Types A and B have 8 RNA segments and encode at least 10 proteins.
Influenza viruses are members of the family Orthomyxoviridae.[2] Influenza viruses A, B, C, and D represent the four antigenic types of influenza viruses.[3] Of the four antigenic types, influenza A virus is the most severe, influenza B virus is less severe but can still cause outbreaks, and influenza C virus is usually only associated with minor symptoms.[4][5][6][7]
Influenza D virus is 50% similar in amino acid composition to influenza C virus, similar to the level of divergence between types A and B, while types C and D have a much greater level of divergence from types A and B.[8][9] Influenza viruses C and D were estimated to have diverged from a common ancestor over 1,500 years ago, around 482 AD.[8] Influenza viruses A and B are estimated to have diverged from a single ancestor around 4,000 years ago, while the ancestor of influenza viruses A and B and the ancestor of influenza virus C are estimated to have diverged from a common ancestor around 8,000 years ago.[10]
Influenza A virus can infect a variety of animals as well as humans, and its natural reservoir (natural host) is birds, whereas influenza viruses B, C, and D do not have animal reservoirs.[4][11][8] Influenza C virus is not as easily isolated so less information is known of this type, but studies show that it occurs worldwide.[12] Influenza C virus currently has 6 lineages, which were estimated to have emerged around 1896 AD.[8]
This virus may be spread from person to person through respiratory droplets or by fomites (non-living material) due to its ability to survive on surfaces for short durations.[4] Influenza viruses have a relatively short incubation period (lapse of time from exposure to pathogen to the appearance of symptoms) of 18–72 hours and infect the epithelial cells of the respiratory tract.[4] Influenza virus C tends to cause mild upper respiratory infections.[13] Cold-like symptoms are associated with the virus including fever (38–40 °C), dry cough, rhinorrhea (nasal discharge), headache, muscle pain, and achiness.[4][14] The virus may lead to more severe infections such as bronchitis and pneumonia.[13]