Originally Posted by J_9
The fever calls the white blood cells to the area of infection. Heat kills bacteria, so fever helps kill bacteria. It also aids in building up our immune systems because then next time our white blood cells see that bacteria, or virus, they stand up and say "Hey, we have already fought you guys once, we know how to get rid of you this time too."
It is remarkable what our bodies do. Once we have a virus or an infection of sorts, that stays in the auto programming of our defense mechanisms.