Molecular evolution of hemagglutinin gene of Influenza A virus.

In the history of human civilization, influenza is the second most catastrophic killer disease for mankind with plague ranking first in the medieval times. The 1918-1919 'Spanish flu' killed 20-50 million people worldwide. According to a report from WHO, there have been four pandemics, several epidemics and recurrent seasonal outbreaks of influenza in different parts of the world. The virus is a potential bioterrorism threat with biological 'Chernobyl-like disaster' that occurred in Soviet Russia in 1977. Here, the author reviews the biology of the surface exposed hemagglutinin of the influenza virus, a gene under constant positive selection pressure to evade host immunity and vaccination. Global, local and seasonal outbreaks of influenza lead to a significant number of deaths both in humans and poultry birds.