Influenza is a negative RNA-strand type virus that can be classified as virus strand types A, B and C. Influenza is a highly contagious virus that in the winter months causes many respiratory tract infections. The most serious are the secondary infections that also can affect the heart and lungs. These include pneumonia, in which the alveoli in the lungs are infected, and myocarditis, when the outer layer of the heart muscle is infected. Chest pain is associated with these secondary supra infections caused by lack of immunity and the lasting effects of the influenza virus in compromised patients. The virus is spread by respiratory droplets and by direct contact that carries infected droplets spread by a sneeze or coughing.
Strand A
Influenza strand A is found in humans, birds and mammals. It is the only type that has been known to be high in epidemic proportions. According to the Centers for Disease Control, influenza strand A has been responsible for all non-avian flu pandemics since the massive Spanish Flu pandemic at the end of World War I. That pandemic affected a fifth of the world's population and killed as many as 50 million people. The CDC states the H1N1 (swine flu), H2N2 and H3N2 viruses all descended from the strand A virus. This is why the CDC refers to the 1918-1919 Spanish flu as the "mother of all pandemics."
Strand B
Influenza strand B is known to generally affect humans only. This type of flu virus can be just as deadly as strand A, but it has not been found to cause pandemics, only epidemics. An epidemic is the lesser of the two and affects fewer people in fewer regions. An epidemic can spread through a town, a city or region and affect many people. The word "pandemic" is used to describe an even larger circulation of an infectious disease. Pandemics usually refer to global infections.
Strand C
Influenza strand C is found in children usually younger than six years of age, and they tend to develop tolerance to it at that time. Strand C does not cause pandemics or epidemics and generally only presents itself as a mild form of the flu.
