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Flu symptoms in humans were described by Hippocrates 2,400 years ago. Since then the virus has caused, in addition to the annual epidemic, many pandemics. Historical data on influenza are difficult to interpret because the symptoms may be similar to those of other diseases such as diphtheria, pneumonia, dengue fever or typhoid. Since 1510 have been about 31 pandemics. The first detailed record of an influenza pandemic occurred in 1850. It started in Asia and spread to Europe and Africa. Pandemics occurred during the seventeenth and eighteenth centuries, being the 1830’1833 particularly virulent and high morbidity, and infectious about a quarter of the exposed population .
The most lethal pandemic known and was called the Spanish flu (virus A, subtype H1N1), which lasted from 1918 to 1919. It is called so because Spain was the country to publish more data on the health disaster that was causing as many censor during the First World War in which they were immersed. Estimates oldest talked about 40 or 50 million deaths caused by it, although the most current estimates put the figure between 50 and 100 million people killed by that flu around the world. This pandemic has been described as the greatest medical holocaust in history, and caused at least as many dead as the Black Death. This high mortality was due to the high rate of infectivity (up to 50 of the exposed population) and the severity of symptoms caused by mass production of cytokines (cytokine storm). To this we must add that the first symptoms in 1918 were attributed to other diseases such as dengue, cholera, or typhoid. An observer wrote that “one of the worst complication is bleeding from the mucous membranes, especially the nose, the stomach or intestine. We are frequent bleeding from the ears and petechial.” Most of the deaths occurred bacterial pneumonia, a secondary infection caused by influenza, but the virus also killed directly as a result of massive hemorrhage and pulmonary edema.
The Spanish flu pandemic was a dubious and even geographical spread throughout the world including the Arctic and remote Pacific Ocean islands. The unexpected severity of the disease caused the deaths of between 2 and 20 of all infected (compared to the normal rate of mortality of the common flu, which is around 0.1 ). Another characteristic of this pandemic was that mortality mostly affects young adults, with 99 of deaths in people under age 65 and over half of adults between 20 and 40 years. 19 The common flu has its highest rates of mortality, in contrast, in the strata of younger population (less than two years) and especially among those over 70. Total mortality of the actual pandemic influenza 1918’1919 is not known with certainty but it is estimated that about 2.5 to 5 of the world died for their cause (about 25 million people only in the first 25 weeks ). Valga as compared to the AIDS virus has caused the same amount of deaths in its first 25 years of existence.
Subsequent pandemics of influenza (Asian influenza (type A, subtype H2N2) and 1968 or the Hong Kong flu (type A, subtype H3N2) have not been so devastating, but also caused millions of deaths. The last pandemic, the availability of antibiotics has been used to control infections and this helps to reduce the mortality rate compared with the Spanish influenza of 18.
Orthomyxoviridae family of viruses is the cause (etiology) of influenza, and was first described in pigs in 1931 by Richard Sch pp. This discovery was shortly followed by the isolation of the virus in humans by a research group directed by Patrick Laidlaw and Medical Research Council of the United Kingdom in 1933. However, it was not until 1935 that Wendell Stanley to establish the true nature of non-cellular viruses.
The first significant step towards the prevention of influenza was to develop a killed virus vaccine by Thomas Francis, Jr. in 1944. Frank Macfarlane Burnet later showed that the virus lost virulence when grown on egg protein, thus enabling the inactivated virus vaccines, more effective.
The application of this observation led to a group of researchers at the University of Michigan developed the first vaccine used in the population, with the collaboration of the army of the United States. The army’s decision to participate in the development of This vaccine was due to his experience with the flu during the First World War, when thousands of soldiers died from the virus in a few months.
While certain fears were unleashed with the pig flu in 1976 in New Jersey in 1977 with an outbreak of influenza in Russia and Hong Kong and other Asian countries in 1997 (with the H5N1 variant of avian flu), there has been no importance of pandemic influenza from Hong Kong, 1968.
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