The flu is unpleasant, contagious and maybe life-threatening. There are three types of regular influenza viruses: A, B and C. Type A influenza is divided into subtypes, such as the H1N1 virus, erroneously called swine flu, and both type A subtypes and type B influenzas are broken down into strains. Both A and B are responsible for causing seasonal epidemics each year, according to the Centers for Disease Control. Influenza C rarely causes widespread illness and results in mild flu symptoms. There are no subtypes of influenza C.
Function
Viruses are constantly evolving. There are two ways a virus can change: antigenic drift and antigenic shift. Drift describes a slow evolution of the virus, while shift is a fast change. Drift rarely causes a problem because its victims build up immunity to the particular strain of influenza and cannot catch it back from whomever they gave it to. Shift causes problems because people cannot build immunity. Type B influenza undergoes only antigenic drift and has never caused a pandemic.
Evolution
Influenza type B affects humans only. Influenza A, however, can jump from one species to another because of its ability to change quickly, or shift. In fact, wild birds are the natural host for all known influenza type A subtypes. One recent antigenic shift occurred in 1997, allowing a strain to jump from wild birds to domestic ones and then on to humans.
Names
Flu can be named by where the outbreak occurs, like the Fijian flu, or it might be called by its host, like the avian flu. Scientists usually refer to the flu subtype, like H1N1. In this reference, the H stands for hemagglutinin, a protein on the outside of a virus that allows it to stick onto its host cell. The N represents the protein neuraminidase, which allows newly formed viruses to exit the host cell.
Symptoms
Influenza types A and B often cause fever, cough, headaches, body aches, chills, fatigue and a runny or stuff nose. H1N1 can cause the additional symptoms of vomiting and diarrhea, according to Flu.gov. People who catch influenza C might experience mild respiratory problems.
Prevention
Hand washing will help prevent the spread of every type of influenza. Flu shots are offered as a preventative measure every winter through a variety of outlets, including doctors offices, pharmacies and health centers. This injection protects against the most common types of A and B influenza and H1N1.
Treatment
Treatment largely depends on the type of virus and the severity of accompanying symptoms and complications. Most influenza viruses are not life-threatening and symptoms go away in a few hours or days. The outcome of the influenza infection depends largely on the severity of the illness, the age and general health of its victim, and whether the person develops complications like pneumonia or dehydration from excessive diarrhea.
