We have two 2-year old cats. They are siblings (male and female) and have been neutered/spayed.
The tomcat has never been very sociable but was friendly enough and liked to be stroked and brushed, but in the last month he has been spending very little time in the house (we have a cat-flap so they can freely go in and out). Especially in the last week he has been coming in only at night, and then running out as soon as he's been fed in the morning, avoiding all contact.
This morning I decided to pick him up after he had finished his meal to check everything was alright but as soon as I did so he viciously attacked me. He was hissing and scratching wildly and drew quite a lot of blood. I had to let him go and he ran straight out again.
I'd be grateful for any advice about what might be causing his this behaviour, and what I can do about it. He doesn't seem to be injured or show any signs of pain when he moves, but I'm thinking to take him to the vet just to be sure. If he reacts this viciously though I'm worried I might not be able to get hold of him at all.
I eventually managed to catch him and take him to a vet, although it took over a month! I couldn't get hold of a trap (I'm in Korea and not fluent in the language so it wasn't so easy), so I had to gradually win back his trust, starting outside where he seemed to be less edgy and them encouraging him back in the house with food. Anyway, the vet couldn't find anything medically wrong with him, and he's slowly got back to his usual self (still anti-social but non-violent, to humans at least!). So I'm still not sure what caused his original lashing-out, but now I'm much more careful to make sure he feels unthreatened before I pick him up... hopefully we won't have any more trouble!