I've read that the FeLV innoculation can mutate into a corona virus, which then mutates into FIP in some cats. I've been advised to never give this innoculation to my cats for this very reason.
Feline Enteric Coronavirus is very contagious. But the mutated form of the virus that causes FIP is not. FIP cannot be passed from cat to cat as the infected cat does not shed the mutated virus. Most cats that are exposed to FCV do not develop FIP.FIP is very contageous and honestly you should hault breeding until you can determine medically that you present breeders are not infected or you can cause a vicious cycle of selling FIP positive cats over and over and signs of FIP may not even occur for years and they can still have it.I hate to sound firm but its a serious matter if indeed it was FIP.