You can't have FIP without Corona, the Corona mutates into FIP, but it doesn't make it so that it's not Corona, it just creates the condition known as FIP (it's not the virus that mutates, it's the condition that mutates, if that makes sense). At least that's how I read it from Dr. Addie's site. It is very rare for a cat with FIP to not show a Corona titer, and I included that explanation below...
FIP occurs when the cat reacts inappropriately to feline coronavirus (FCoV) infection. Most cats simply become infected, shed FCoV for a month or two, mount an immune response, eliminate the virus and live happily ever after. However, for reasons that we don't yet fully understand, instead of clearing FCoV infection, an unfortunate few cats develop FIP. The presence of antibodies indicates that the cat has been infected with FCoV, the cause of FIP. Any FCoV antibody titre can occur in cases of wet or effusive FIP, but most cats with FIP have extremely high antibody titres (1280 or greater). Antibody titres of 0 are unusual in FIP cases and are usually considered as indicating that the cat does not have FIP. (However, if other parameters suggest a diagnosis of FIP, despite having an antibody titre of 0, then this is the one situation where FCoV RNA detection (RT-PCR), performed on a sample of the effusion, is diagnostic of FIP. In these cats there is so much virus in the effusion that all the antibody is bound to it, and none is available to bind to virus in the test.) Phaewryn http://ucat.us Adopt a New England FIV+ cat: http://ucat.us/FIVadopt.html Special Needs Cat Links (and feline info library): http://ucat.us/domesticcatlinks.html Declawing Creates SUFFERING, Please don't declaw! http://www.pawproject.com/kona.html