Influenza
Influenza, commonly known as the flu, is a contagious disease caused by a virus infecting the reparatory tract. Influenza viruses are divided into three types, designated as A, B, and C. Influenza type C usually only causes either very mild symptoms or no symptoms at all. Types A and B, however, are responsible for epidemics of respiratory illnesses that can result in hospitalization, or even death. (6) Influenza is constantly changing over time by mutations. This continual change allows the virus to evade the antibodies that were meant to kill it. This causes people to be susceptible to influenza infection throughout their entire life. The old antibody may provide partial protection against infection because the viruses are so similar. There are currently four main strains of influenza circulating worldwide. Three of the viruses are type A, and one is type B. Type A viruses are divided into subtypes based on the differences in two viral proteins called hemagglutinin (H) and neuraminidase (N). The three subtypes of influenza A are A(H1N1), A(H3N2), and A(H5N1). The reason for several strands of type A are because of the two kinds of change influenza A undergoes. The first is a series of mut
Prior to this discovery, the A(H5N1) virus was only known to infect various species of birds. To do this, they combined the vaccine against type B with vaccines against the subtypes of type A as they evolve. This type however had a lower mortality than that caused by the two previous pandemic viruses. html American Lung Association7) kidshealth. (1) In response to the ever-changing influenza virus, scientists have had to find a way to create an effective immunity. Of the other influenza strands circulating worldwide, A(H3N2) still has the most severe impact. This time, however, influenza type A(H2N2) was responsible. edu/patients/IHB/peds/infectious/pedsinfluena11) www. This meant that the existing antibody could provide some protection against the virus. From 1918 to 1919 the "Spanish flu" caused the highest known influenza related mortality.
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