One day we were playing with our dog and noticed a hotspot on her neck. After this we immediately checked for fleas. Our dog rarely gets fleas. Usually we use Advantage, but our local store ran out. The only thing we had available was Hartz and a few other flea tick medications. We picked up the Hartz came home and applied. (No, we had not washed her in the past 48 hours.) A few days later we noticed missing hair. She has tried to bite me a few times since and sometimes she rapidly shakes. We are taking her to the vet today.