CATS · OWNER EDUCATION
Feline Infectious Peritonitis (FIP)
Feline infectious peritonitis, or FIP, is an inflammatory illness associated with feline coronavirus. Most coronavirus-exposed cats do not develop FIP. Disease can affect the abdomen, chest, eyes or nervous system.

THE SHORT VERSION
What matters for your animal?
Start with the warning signs and when-to-contact sections if your animal is unwell. The same outward change can have several causes, so this guide helps you prepare questions rather than identify a diagnosis on your own.
What is this condition?
Feline infectious peritonitis, or FIP, is an inflammatory illness associated with feline coronavirus. Most coronavirus-exposed cats do not develop FIP. Disease can affect the abdomen, chest, eyes or nervous system.
FIP is not diagnosed from one vague sign such as fever or a swollen abdomen. The veterinarian combines the pattern of illness with examination findings and appropriate samples or imaging. Tests need careful interpretation because exposure to feline coronavirus is not identical to a diagnosis of FIP. Ask which findings support the diagnosis and how current treatment access and monitoring will be handled.
Which species does this guide cover?
The species listed above are the focus of this guide, rather than a complete list of every animal that can develop this condition. Causes, testing and treatment may differ between species and individual patients.
Why can it happen?
- Viral changes within an infected cat and the immune response contribute. Young cats and crowded environments are important risk settings, but older cats can develop disease.
An infectious illness depends on both the organism and the animal's ability to resist it. Exposure does not always produce the same severity of illness in every animal. Age, previous immunity, nutrition, stress, and concurrent disease can influence the outcome. The infection may also cause complications that need treatment separately from the organism itself. For example, correcting fluid loss or supporting breathing can be essential even when a targeted medicine has already been started.
What might an owner notice?
- Persistent fever, weight loss, poor appetite, abdominal swelling, breathing changes, eye inflammation or difficulty walking.
How is the problem investigated?
Diagnosis combines history, examination, blood results, imaging and sometimes fluid or tissue testing. A positive coronavirus antibody test alone does not diagnose FIP.
Molecular testing, such as PCR, looks for genetic material from a target organism in the submitted sample. It can be useful, but the meaning depends on the sample site, timing, and disease. Detecting material is not always the same as proving that the organism explains every sign, while a negative result may not exclude infection if sampling or timing was unsuitable. The veterinarian interprets the result alongside the examination and other findings rather than treating it as an isolated verdict.
Imaging provides information about location, size, shape, and structural changes. Radiographs and ultrasound often answer different questions, so one does not simply replace the other. Images may reveal a complication or guide sampling without establishing the exact microscopic cause. Some procedures require sedation or anesthesia to obtain accurate images safely. Ask what the proposed study is expected to clarify and how its possible results would influence treatment, further testing, or referral.
Blood-cell testing and a chemistry profile provide complementary information. Cell counts can help assess anemia, inflammation, and platelets; chemistry measurements help assess organs and internal balance. Results are interpreted against the species, examination, hydration, medication history, and previous values. A value just outside the reference interval is not automatically the cause of illness. Trends can be more useful than one result, particularly when the aim is to monitor a chronic problem or check that treatment remains safe.
What might treatment involve?
Veterinarian-supervised antiviral treatment has changed the outlook. Availability and prescribing rules vary by location; monitoring and treatment duration require professional guidance.
This is an overview, not a prescription or a recommendation for a specific individual animal.
What can owners do at home?
Record weight, appetite and activity and follow laboratory rechecks. Discuss hygiene and the needs of other household cats.
A feeding plan should account for the actual food eaten, not just the amount offered. Selective eating, dropped food, hidden leftovers, and competition can make intake difficult to judge. Record the food type, measured portion, treats, and any supplements so the team can assess the complete diet. A disease-specific diet or assisted feeding may be recommended in some cases, but force-feeding is not a safe default for an animal that cannot swallow normally or may have an obstruction.
Avoid actions that could make care less safe.
- Do not purchase unverified injections or assume internet dosing applies to your cat. Do not diagnose FIP from one test result.
What can the longer-term outlook involve?
Many treated cats can recover, but disease severity, complications and response matter. Relapse or another diagnosis may require reassessment.
A recheck is not simply a repeat of the first appointment. It assesses whether the original problem is improving, whether complications are appearing, and whether the treatment remains appropriate. The useful measures may include comfort, function, intake, body weight, examination findings, or selected tests. Ask which changes are expected before the visit and which should trigger an earlier call. Improvement in one sign does not always mean that every part of the disease has resolved.
Can risk be reduced?
Reduce crowding and maintain litter hygiene. No household measure guarantees prevention.
When should you arrange care?
- Seek emergency care for breathing difficulty, seizures or major weakness; persistent fever and weight loss need prompt investigation.
Seek urgent veterinary advice if you notice:
DO NOT DELAY URGENT CARE- Seek emergency care for breathing difficulty, seizures or severe weakness.
What information helps the care team?
Write down when changes started, what makes them better or worse, actual food and water intake, and all medicines and supplements. Short videos and a medication-label photo can help describe changes that may not appear during the appointment.
How should you understand the tests?
Ask what each proposed test is intended to answer. Some tests identify a cause; others assess severity, organ function or treatment safety. Results are interpreted with the examination and history. A normal result does not exclude every problem, and an abnormal result does not always explain every sign.
Questions to ask before leaving
- What is confirmed, and which other explanations are still being considered?
- What changes should we expect with the proposed plan, and when should we reassess if they do not occur?
- Which observations should I record, and which changes mean I should call sooner?
- What medicine or home-care problems should I report, and what are the instructions for a missed dose or suspected side effect?
- When is the recheck, what will it assess, and whom should I contact after hours?
A care plan may be adjusted as results or the response become clearer. Keep the written instructions and tell the team if cost, handling or administration difficulty makes the plan hard to follow.
Sources behind this guide
Feline Infectious Peritonitis | Cornell University College of Veterinary MedicineVeterinary, university or animal-health guidance ↗Content last reviewed: October 3, 2026. Review status: veterinary-informed; independent veterinarian review not yet completed.
