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 mu
(3) All three of the pandemic viruses and the new A(H5N1) are believed to have originated from animals. (5) ------------------------------------------------------------------------**Bibliography**. It is believed that the "Spanish flu" in 1918 was contracted through a pig, while the "Asian flu" and "Hong-Kong flu" are believed to have come from some type of bird. In May of 1997, influenza A(H5N1) was isolated from! a child who died with Reyes Syndrome in Hong Kong. These neuraminidase inhibitors, like zanamivir (Relenza), has recently been given a Notice of Compliance with Conditions, allowing it to be sold in Canada for the treatment of influenza. Even though in 1968, the A(H3N2) virus only caused a moderate mortality, it has continued to circulate and evolve. In the years since its emergence in 1968, type A(H3N2) epidemics have caused more than 400,000 deaths in the United States. They have tried to solve this problem by creating polyvalent vaccines. In 1976, a new influenza virus from pigs caused human infections and severe illness. (4) The "Hong-Kong flu" in 1968 marked the emergence of the influenza type A(H3N2). Although the exact means of transmission of A(H5N1) has not been identified, it is believed to have come through contact with infected birds, not human to human transmission. (1) When antigenic shift occurs, large numbers of people have no antibody against the virus. Prior to this discovery, the A(H5N1) virus was only known to infect various species of birds. It periodically causes epidemics, but none as severe or as deadly as in 1918. So, a new class of antiviral medications is able to inhibit both influenza A and B.
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