Thank you for your replies...you have definitely made me feel better. It's comforting to know that a safe environment, good diet and lots of love can make all the difference! Also, I don't have other cats, just a turtle (although I was considering getting Charlie a playmate, but I guess not...), so there won't be any danger of spreading. Charlie's mom and brother live in another home.
Spencer, I agree with you that this is a terrific forum. People always have a kind word for one another and are always willing to offer their advice and support. It is very refreshing to me, as I have come across people who have never had pets, don't like animals(?!?) and can't understand the special bond that exists between people and their pets. They don't know what they're missing!!