Influenza - Description

The flu is often confused with the common cold (see common cold entry), but it is actually much more serious. The annual death toll due to influenza and its complications averages twenty thousand in the United States alone. Sometimes, a flu epidemic sweeps across a wide part of the world, killing large numbers of people. An epidemic is a sudden, rapid spread of a disease through a large geographical area. In 1918–19, a form of influenza known as the Spanish flu spread throughout the world. The death toll from the epidemic was estimated at twenty million to forty million people. About five hundred thousand of those deaths occurred in the United States.

Influenza outbreaks occur on a regular basis. An influenza epidemic occurred in 1957 and again in 1968. The first of these outbreaks was known as the Asian flu. The second was called the Hong Kong flu. About seventy thousand Americans died of the Asian flu and about thirty-four thousand from the Hong Kong flu.

Influenza has been known for more than 2,500 years. The ancient Greek physician Hippocrates was one of the earliest writers to describe the condition. Throughout most of history, people blamed the disease on a number of factors, including various kinds of bacteria and "bad air." In 1933, however, researchers found the real cause of the disease: a virus.

Three types of influenza viruses have now been discovered: types A, B, and C. Type A virus can infect many different kinds of animals, including humans, pigs, horses, and birds. Viruses B and C infect only humans. Influenza A is responsible for most cases of the disease in humans. Types B and C are less common and produce a milder form of infection.