I had a cat with that. We had no idea until he was really sick. None of our other cats caught it. It was pretty sad when he died, but he was around 10 or 11 yo. I think if you look after them right, keep them on good food & not too over weight, they will have a better chance of living longer & uneffected.

Best of luck. But it's not a short-term death sentence.

I am surprised the RSPCA didn't vaccinate!