<P> From a public health point of view, flu epidemics spread rapidly and are very difficult to control . Most influenza virus strains are not very infectious and each infected individual will only go on to infect one or two other individuals (the basic reproduction number for influenza is generally around 1.4). However, the generation time for influenza is extremely short: the time from a person becoming infected to when he infects the next person is only two days . The short generation time means that influenza epidemics generally peak at around 2 months and burn out after 3 months: the decision to intervene in an influenza epidemic therefore has to be taken early, and the decision is therefore often made on the back of incomplete data . Another problem is that individuals become infectious before they become symptomatic, which means that putting people in quarantine after they become ill is not an effective public health intervention . For the average person, viral shedding tends to peak on day two whereas symptoms peak on day three . </P> <P> The word Influenza comes from the Italian language meaning "influence" and refers to the cause of the disease; initially, this ascribed illness to unfavorable astrological influences . Changes in medical thought led to its modification to influenza del freddo, meaning "influence of the cold". The word influenza was first used in English to refer to the disease we know today in 1703 by J. Hugger of the University of Edinburgh in his thesis De Catarrho epidemio, vel Influenza, prout in India occidentali sese ostendit . Archaic terms for influenza include epidemic catarrh, la grippe (from the French, first used by Molyneaux in 1694), sweating sickness, and Spanish fever (particularly for the 1918 flu pandemic strain). </P> <P> The symptoms of human influenza were clearly described by Hippocrates roughly 2,400 years ago . Although the virus seems to have caused epidemics throughout human history, historical data on influenza are difficult to interpret, because the symptoms can be similar to those of other respiratory diseases . The disease may have spread from Europe to the Americas as early as the European colonization of the Americas; since almost the entire indigenous population of the Antilles was killed by an epidemic resembling influenza that broke out in 1493, after the arrival of Christopher Columbus . </P> <P> The first convincing record of an influenza pandemic was of an outbreak in 1580, which began in Russia and spread to Europe via Africa . In Rome, over 8,000 people were killed, and several Spanish cities were almost wiped out . Pandemics continued sporadically throughout the 17th and 18th centuries, with the pandemic of 1830--1833 being particularly widespread; it infected approximately a quarter of the people exposed . </P>

The flu is caused by a dna virus