Overview of FIP
Feline infectious peritonitis (FIP) is a serious, nearly always fatal systemic viral disease of wild and domestic cats caused by a coronavirus, a type of virus that afflicts pigs, dogs, and in some forms, humans. However, the specific virus that causes FIP—the FIP virus—does not infect humans. The clinical name for the virus that causes FIP is feline coronavirus. (FcoV).
A common, relatively benign form of feline coronavirus is the feline enteric coronavirus (FECV). When FECV mutates into a disease-causing form, it is called FIPV (feline infectious peritonitis virus). If a cat's immune system responds poorly, the mutant FECV may cause the systemic infection called FIP.
The onset of feline infectious peritonitis may be sudden, especially in kittens. The disease often develops so gradually that the infection is well established before overt symptoms appear. When FIP symptoms become apparent, they often include small tissue abscesses (pyogranulomatous lesions) in the liver, kidneys, and the membrane that lines the abdomen (peritoneum); and fluid accumulation within body cavities.
Incidence and Prevalence of FIP
There are two strains of FIPV. The Type I strain, or FCoV-1, is believed to cause about 85% of all identified FIP cases. The less common Type II strain, or FCoV-2, accounts for the rest. FIPV probably affects less than 1% of the cats brought to veterinarians for treatment.
Coronavirus infections are common in cats, especially those in catteries and shelters where large numbers of kittens and adult cats share living space. It has been estimated that 80% to 90% of all the animals in multi-cat households where FECV is present become infected.
The prevalence of FIPV, on the other hand, remains low in the wild and domestic cat populations, probably less than 2%. In multi-cat households or catteries where the disease is present, it can be as high as 10%. In some shelters and catteries, the disease rate can be as high as 20% over a period of several months.