[1][6] Influenzaviruses C and D were estimated to have diverged from a single ancestor over 1,500 years ago, around 482 AD.

[7] Metatranscriptomics studies have also identified closely related "Influenza C and D-like" viruses in several amphibian and fish species.

[5][10][1] Influenza viruses C and D are not as easily isolated so less information is known about these types, but studies show that they occur worldwide.

[1][6] This virus may be spread through respiratory droplets or by fomites (non-living material) due to its ability to survive on surfaces for short durations.

[5] 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.

Fusion of these membranes allows the viral proteins and genome to be released into the host cell, which then causes the infection.

When either of these processes occur, the antibodies formed by the immune system no longer protect against these altered glycoproteins.

[17] Hemagglutination inhibition (HI) is one method of serology that detects antibodies for diagnostic purposes.

[10] Influenza viruses A and B also cause seasonal epidemics every year due to their ability to antigenic shift.