As you would have heard the thought that " Prevention Is Better Than Cure " 
I am going to explain you by an example ... which is : "If mahesh is sick and he know that it is a hazardous sickness but he didn't visit a doctor and he became sick ." If mahesh would have visited the doctor then he would have not been sick  ( Most probably ) .This was prevention . control means that mahesh is now being treated by a doctor.