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 mu

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When antigenic shift occurs, large numbers of people have no antibody against the virus. This may result in a worldwide epidemic called a pandemic. Throughout this century there have been three pandemics, which occurred in 1918, 1957, and 1968, each resulting in a large number of deaths. (1) The first and most devastating began in World War I. From 1918 to 1919 the "Spanish flu" caused the highest known influenza related mortality. The influenza virus responsible for the 20 million worldwide deaths was type A(H1N1). The "Asian flu" arose in 1957 causing about 70,000 deaths in the United States alone. This time, however, influenza type A(H2N2) was responsible. Finally in 1968, influenza type A(H3N2) killed nearly 34,000 Americans. Known as the "Hong-Kong flu" it is the most recent of the pandemics. (6) Recently, the world has been concerned with another type of influenza that could possibly cause the next pandemic. In May of 1997, influenza A(H5N1) was isolated from!

n and/or the neuraminidase. It is possible for influenza type B to undergo the gradual process of antigenic drift. (1)

The "Hong-Kong flu" in 1968 marked the emergence of the influenza type A(H3N2). This type however had a lower mortality than that caused by the two previous pandemic viruses. The lower mortality is believed to have happened for two reasons. First, only hemagglutinin changed from the "Asian" strand [A(H2N2)]. This meant that the existing antibody co

Some common words found in the essay are:
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Approximate Pages = 4 (250 words per page double spaced)