The University of South Carolina states that although many upper respiratory diseases are called flu, there are truly only three different types of flu virus, all belonging to the orthomyxovirus family. The university adds that the virus can be spread through the air and to a lesser extent through touch. Incubation, or the time it takes to present symptoms after being exposed to the virus, takes 18 hours to three days. Major outbreaks are caused by Types A and B. Type C presents with minor symptoms.
Type A Influenza
Type A flu virus lives in ducks and other animals and may be passed to humans. The Centers for Disease Control and Prevention explains that Type A may mutate while living in a host animal, changing the chemical makeup of the virus over the flu season. With each new mutation, a new antibiotic may be needed, making it harder to find effective treatments. Prior to 2009, the Type A H1N1 virus was a regular virus, until it mutated and became the cause of the 2009 pandemic. Another Type A flu virus causing concern as of 2010 is H5N1, or avian flu.
Type B Influenza
Type B influenza does not live in or spread from host animals. The University of South Carolina states it is theorized that due to the lack of an animal reservoir where most mutations occur, Type B influenza appears to have very little change in its chemical makeup throughout the entire flu season. This means an antibiotic will remain effective against Type B influenza for the length of that period. The university adds that Type B virus has been the major cause of influenza outbreaks in past years.
Type C Influenza
The CDC reports that because the symptoms of Type C virus include only mild respiratory illness and do not cause epidemics, vaccines are rarely made. The University of South Carolina explains that there are two types of vaccines for influenza. Both are incubated in eggs, yet one is grown from the active virus and the other from the inactive. Whichever virus is predicted to be of greatest concern for any given flu season is the one that is grown.
