Feline infectious peritonitis
Also called FIP
A serious disease that develops in a small number of cats infected with the common feline coronavirus. Young cats under 2 years are most often affected, with fever, weight loss and sometimes fluid in the belly or chest.
Cause and spread
- Cause
- A mutated form of feline coronavirus (FCoV) that spreads in the cat's body and inflames blood vessels in any organ.
- How it spreads
- The ordinary coronavirus is spread in faeces, through litter trays and grooming, and most infected cats stay well. FIP develops inside an individual cat after the virus mutates, often after stress.
Signs to watch for
- Fever that does not respond to treatment, poor appetite and weight loss
- Swollen belly or breathing difficulty from fluid in the abdomen or chest
- Yellow gums and eyes
- Eye changes and nerve signs (wobbling, seizures) in some cats
- Mostly cats under 2 years old
Many diseases look alike. Only a laboratory test can tell them apart, so please see a veterinarian for any sick animal.
How it is diagnosed
FIP can be hard to diagnose. If there is fluid, testing it is the single most useful step: cytology, protein levels and detection of the coronavirus by RT-PCR. Without fluid, fine-needle samples from affected organs are tested. Blood tests are supportive: a low albumin-to-globulin ratio, high globulins and high bilirubin suggest FIP. Antiviral treatment is available in some countries, and a fast response supports the diagnosis.
- Usually the first testCytologyExamines cells in effusion fluid.
- Confirms the diseaseFeline Infectious Peritonitis (FIP) PCRDetects the coronavirus in fluid from the belly or chest, or in aspirates from affected organs.
- Supports the diagnosisFine Needle Aspiration Cytology (FNAC)Examines cells from affected organs and lymph nodes.
- Supports the diagnosisComplete Blood Count (CBC)Often shows low lymphocytes and mild anaemia.
- Supports the diagnosisTotal BilirubinOften raised in FIP.
Prevention and control
- Reduce stress and crowding in multi-cat homes
- Keep litter trays clean and separate from food
- Isolate and test cats with unexplained fever or fluid, and talk to your veterinarian early
Where this information comes from
- Feline Infectious Peritonitis (ABCD guideline) · European Advisory Board on Cat Diseases (ABCD)
General information for animal owners and veterinarians, last checked October 2026. It does not replace the advice of your veterinarian, who should decide which tests and treatment your animal needs.