I have a pair of cats – brothers – rescues, as all my cats have always been, and at the time I also had an older female. These sweet boys are my angels, and naturally I did not want them getting bugged by fleas, so, even though they are strictly indoor, I got them all Hartz flea collars. Within a day all were sick – drooling, unable to eat, listless. It didn’t occur to me at first that the collars were the problem, but when I called the vet, that was the first thing he asked. Apparently, by grooming each other, they were getting doubly sick from the collar’s poison.
Needless to say I removed them immediately, and the larger brother recovered quickly – the smaller brother took longer, and the female never completely recovered. She continued to lose weight and seemed emotionally traumatized. The boys kept her company and comforted her as best they could, but rather than living another few years, as she ought to have, since she had been in good health and was only 12 years old, she slowly faded and died less than 6 months later.