We have a houseful of cats. We've added another in the last year. He lives outside but does come in occasionally. His name is Max. He was an adult when he came to us full of battle scars so he's probably lived outdoors his whole life. He was lying in the yard the other night and when he started to walk, it looked like he was drunk. He's been to the vet today and a blood test has confirmed that he has feline leukemia :( He's also contagious to other cats. The other cats have had their regular shots but I don't think there is one for feline leukemia?
We're going to put Max down after we've all had a chance to say goodbye to him. Apparently this is common in old tom cats per the vet.