Humans have been battling disease since the dawn of time, and the most frightening of all diseases is the widespread infectious disease. In just a few short years, the threat of a major epidemic has become abundantly clear. In particular, the H 1 N 1 pandemic has been surprisingly rapid and widespread. This aroused people's vigilance. 
The virus is becoming more and more insidious.
 the human fight against infectious diseases has no end period.