History of Influenza Pandemics

Influenza pandemics have been amongst the largest and the deadliest epidemics in the history of man, and were observed already in ancient times. For example, records from the fifth century B.C. suggest that influenza pandemics were observed in ancient Greece. In Europe, during the Middle Ages and the Renaissance, numerous concordant reports from different countries describe epidemics of respiratory infections that resemble influenza pandemics. However, it is not possible to be certain that these epidemics were due to influenza. In the twentieth century, three influenza pandemics have occurred, including the deadly Spanish flu pandemic. Modern virology has unravelled the mechanisms of emergence of pandemic viruses, and considerable knowledge on influenza viruses has been accumulated. The picture is now clear: influenza A is a zoonotic virus whose reservoir is in wild birds. In rare cases, these avian viruses are introduced into man and, eventually, become pandemic viruses. Although these mechanisms are now understood, the time frame required for adaptation of the avian virus to its new host remains unknown. Maybe the next pandemic will show us how rapid this adaptation can be.