Here in Arizona we have Ehrlichia - Tick Fever. It will very slowly kill the dog if not caught in time. While we don't have near the problem with fleas we have to worry about ticks so I Protical every month.
P.S. One of the easiest ways to kill a tick is to remove it from the dog - head and all - and put it in a small glass of booze. I have taken in many rescues that we have pulled over 50 ticks at a time. So sad.
