Initial exposure to the FIP virus usually does not result in obvious symptoms. However, some cats do experience a mild respiratory disorder characterized by sneezing, watery eyes, and aqueous discharge from the nose. Other cats may have soft abdominal disorders. Most cats that go through the primary infection get over it entirely, but some may become carriers of the virus. Only a small percentage of cats exposed to develop the deadly disease – weeks or even months after the primary infection.
The onset of clinical signs of the deadly FIP may be sudden (especially in kittens), or the symptoms may slowly become stronger. Many cats have non-specific symptoms such as variable appetite, depression, coarse coat, weight loss, and fever.
The most important forms of FIP are the effusive (wet) FIP, non-effusive (dry FIP), and a combination of both. The most characteristic symptom of wet FIP is the accumulation of fluid in the abdominal cavity and/or chest. When the amount of fluid becomes too much, the cat may have difficulty breathing.
The start of dry FIP is slower. Dry FIP accumulates a minimal amount of fluid, while weight loss, depression, anemia, and fever are almost always present. In addition, signs of kidney failure, increased fluid intake and urination, liver failure (jaundice), pancreatitis (vomiting diarrhea and diabetes), neurological disease, balance disorders, behavioral changes, paralysis, convulsions, vomiting, diarrhea and eye disease (inflammation and/or loss of vision) can occur in various combinations.
FIP is a difficult disease to diagnose because each cat shows an individual disease pattern with symptoms that are similar to many other conditions.