Sudden Aggression

Question
Hi, we have three cats. Two males who are brothers and grew up together and a female that was introduced over a year ago. Recently the oldest male cat has snapped and attacked his brother. We separated them for a night and let him out the next day. He was fine for a week. He didn't seem himself though, he became very timid and would get spooked over the smallest noise. He has also became more aggressive with his affection. He has always been the type of cat to show his love with nibbles and bites. The first time this happened, we put him in a pet carrier to show that the other cats wouldn't hurt him. He would hiss and growl and do circles in the carrier and attack the door. Over the past week he seemed that whatever it was that made him snap was gone, then it happened again, this time he hurt his brother and we had to separate them again. We had them apart for almost four days, introducing them through the door and letting them sniff each others face. We let him back out last night. He was around both cats and was fine for about ten minutes and then he snapped again and started hissing and growling. If we put the other two cats away he will turn his aggression on us. I notice the first time this happened, I went into the room with him after a few hours to see if he was okay and he was purring and liked getting attention and then he would put his ears back and start to growl at me. We took him to the vet and physically hes a healthy cat. We have a Feliway diffuser that is supposed to calm cats in situations like this, but it hasn't help him. Do you think something is wrong with him mentally? He will have these fits and then turn into a completely different cat, like someone turning on a switch. Please help. The vet said it might lead to him being put down if it becomes a serious enough issue. Thanks for your time.

Answer
Hi Jenn,

Aggression like this is usually triggered by something your cat has seen. Most likely he got a glimpse of another cat outside. Check to see if he can see through the windows or the door to outside. If he can you need to make sure he can't. This will remove what is setting him off.

Since the re intro worked for a bit I would keep at it. I would take a little more time to do it though. Keep up with the Feliway. Ask your vet about a little Valium for your cat to keep him calm while you are reintroducing him again. Also when you take any of your other cats to the vet make sure you take him along. The vet visit, (strange cat smells), can trigger an episode. The biggest thing you can do though is to remove the trigger that is causing this aggression. If  you do this all will be better. It just will take a little time. Good luck.

Ciao, Karen