Modern antiviral treatment has changed the prognosis considerably. Suspected FIP therefore does not, in itself, mean that a cat cannot be treated. Prompt investigation aims to assess how likely the diagnosis is and start appropriate treatment before severe organ damage develops.
When to see a vet urgently
Seek emergency care immediately if your cat develops any of the following:
- Difficult breathing, open-mouth breathing or an inability to rest.
- Seizures, collapse or an inability to walk normally.
- An eye that suddenly becomes painful or apparent deterioration in vision.
- Abdominal swelling with deterioration in general condition, or loss of appetite.
Persistent fever, weight loss or failure to grow in a kitten also needs investigation. You can find a vet near you.
Overview
FIP develops in only some cats infected with coronavirus, when the virus mutates within the body. An abnormal immune response is central: instead of protecting the cat, it causes severe inflammation in blood vessels and tissues. The forms of the disease are:
- Wet (effusive): fluid accumulation in the abdominal or chest cavity.
- Dry (non-effusive): granulomas form in organs such as the liver, kidneys, central nervous system and eyes.
These forms are not entirely separate diseases: the same cat can have both fluid accumulation and organ changes, and the pattern of symptoms may change. A granuloma is a focus of inflammatory cells. Eye and neurological signs can also occur in cats with fluid in body cavities.
Ordinary enteric coronavirus is common, particularly in environments with several cats. Finding it does not mean a cat will inevitably develop FIP. Shedding FCoV in faeces and diagnosing FIP are different things, so a positive faecal sample in a cat without symptoms is not interpreted as a diagnosis of FIP.
Causes
FIP results from a combination of coronavirus infection and an abnormal immune response. Factors that favour its development include:
- Large numbers of animals, such as in catteries, homes and multi-cat households.
- Stress, including moving home, neutering or a change of environment.
- An inherited predisposition in certain breed lines.
- Age: young cats under two years and older cats are at risk.
- Chronic infections and a weakened immune system.
These factors may increase exposure or be associated with disease, but a single house move or neutering procedure does not establish the cause of FIP. Not all young cats or cats carrying coronavirus become ill. Besides animal numbers, infection pressure is affected by space, hygiene, the number of kittens and turnover within the group.
Risk factors
The disease occurs more often in:
- Kittens and young cats.
- Animals from catteries or homes with many cats.
- Cats experiencing ongoing stress.
- Pedigree cats, such as Birmans, Bengals and Abyssinians.
Breed-related findings vary between the populations studied. They do not predict whether an individual cat will become ill. Genetic tests cannot reliably select cats resistant to FIP either. Older and non-pedigree cats can develop the disease, although it is diagnosed particularly in young cats.
Symptoms
The clinical picture depends on the form of FIP:
Wet form:
- Abdominal swelling (ascites).
- Breathing difficulties if fluid accumulates in the chest.
- Tiredness and weight loss.
- Fever that does not respond to antibiotics.
Dry form:
- Chronic fever.
- Weight loss.
- Eye inflammation, including uveitis, cloudiness and haemorrhages.
- Neurological problems, including ataxia, seizures and paralysis.
- Effects on the liver and kidneys.
In a growing kitten, poor weight gain may be a sign even when fluid is enlarging the abdomen. Some cats develop yellow mucous membranes or whites of the eyes. Describe any changes in behaviour, unsteadiness or changes in eye colour and clarity to the vet.
The symptoms are not specific to FIP. Fever persisting despite antibiotics does not confirm the disease on its own, and abdominal fluid does not automatically mean FIP. Cancer, heart disease or other inflammation can produce similar findings, for example. The cause of breathing difficulty must be investigated quickly whether or not FIP has already been diagnosed.
Complications and consequences
FIP leads to:
- Severe systemic inflammation.
- Damage to vital organs, including the liver, kidneys and brain.
- Chronic pain.
- Death.
This list describes possible consequences, particularly of untreated or severe disease. Effective antiviral medication means death is no longer an inevitable outcome. However, severe illness at the outset and existing organ damage may worsen the prognosis, so simply starting medication does not replace supportive care.
Diagnosis at the vet
An accurate diagnosis is difficult because there is no single test that confirms FIP. Investigations include:
- Blood tests, which may show anaemia, high globulins and low albumin.
- Coronavirus serology and PCR testing: distinguishing FCoV from the mutated virus is not always possible.
- Fluid analysis: thick yellow fluid with a high protein content.
- Ultrasound and X-rays to assess fluid and granulomas.
- Tissue histology, the gold standard.
Coronavirus antibodies show exposure, not FIP on their own. A negative antibody result is also interpreted alongside the other findings. Faecal PCR assesses shedding of enteric coronavirus, whereas examining accumulated fluid or abnormal tissue can help investigate the disease itself. The sampling site determines which question the test answers.
Fluid is examined for its composition and cells and, when needed, viral genetic material or antigen, meaning components of the virus. Yellow colour or high protein alone is insufficient for diagnosis. Without fluid accumulation, tests may target organs or lymph nodes found to be abnormal on imaging.
Characteristic inflammatory changes in a tissue sample, together with detection of viral antigen, can confirm the diagnosis. However, investigations and the start of treatment are considered together in a seriously ill cat; not every sample can always be collected safely. Response to treatment supports the overall assessment, but improvement in uveitis with antiviral medication, for example, does not prove FIP on its own.
Treatment
- Until recently, FIP was considered fatal, but it is now successfully treated with antiviral medicines such as GS-441524, remdesivir and, less often, molnupiravir. The vet determines the treatment duration, and most cats recover.
- Medicine availability varies between countries. The vet prescribes the treatment plan, dose and monitoring tests. Treating your cat yourself with online products of unknown composition is dangerous.
- Fluid accumulated in the chest is drained to ease breathing, and supportive care is also given.
The treatment duration often used in the past is not the same for every cat. Shorter treatments have also succeeded in selected situations, but duration is determined by the disease presentation, the medicine used and monitoring findings. Do not shorten treatment because your cat seems brighter or apply another cat's treatment plan.
Eye and neurological disease may affect the choice of medicine and how treatment is given. The medicine options are not directly interchangeable. The vet monitors condition, weight and relevant blood values, and checks that medication remains appropriate as weight changes. A product of uncertain origin may not contain what its label claims.
Supportive care helps with problems such as breathing difficulty, pain, nausea and dehydration. If your cat cannot obtain enough nutrition, a plan to support eating is needed. Forcing food into a weak cat's mouth is not helpful. Hospital care may be necessary early on, even after antiviral treatment has started.
The earlier treatment starts, the better the prognosis, so seek veterinary care promptly for persistent fever, abdominal swelling or breathlessness in a young cat.
Home care, check-ups and prognosis
Record appetite, weight changes, activity, ease of breathing and any eye or neurological signs. Report difficulties giving medication or a return of symptoms. If the expected improvement does not occur, the vet reassesses the diagnosis, whether treatment is being delivered successfully and any concurrent illnesses.
Agreed check-ups continue after symptoms improve. Treatment is not ended solely because the abdomen is smaller or your cat has one good day. Many cats recover well, but relapse or severe organ damage is possible. The prognosis is refined according to treatment response, and using a particular medicine does not guarantee recovery.
Prevention
You cannot protect your cat completely from FIP, but you can reduce the risk through:
- Managing the number of cats at home: no more than three or four.
- Keeping litter trays clean, as the virus spreads through faeces.
- Minimising stress.
- Taking FCoV risks into account when breeding.
- Vaccination: a vaccine exists, but its effectiveness is disputed and it is rarely used.
There is no single number of cats below which the risk of FIP disappears. Adequate space, clean litter trays and resources that reduce stress are essential. Removing faeces and cleaning equipment reduces faecal exposure to FCoV, but cats without symptoms can also shed the virus.
Routine FIP vaccination is not recommended because there is insufficient evidence of clinically meaningful protection. Ordinary cat vaccinations do not protect against FIP. If a cat in a household becomes ill, discuss the other cats and any infection control measures with the vet; a positive FCoV test alone is no reason to regard every cat as having FIP.
What it means for owners
Feline infectious peritonitis is one of the most dangerous viral diseases and requires particular attention. Remember that chronic fever, ascites or neurological signs need immediate veterinary assessment. Modern antiviral medicines, such as derivatives of GS-441524, have shown effectiveness, but they are not always available and require close professional monitoring.
Note: this material provides general information and does not replace veterinary treatment advice. Contact a vet immediately if symptoms develop.
Frequently asked questions
Does a positive coronavirus test mean FIP?
No. Antibodies indicate exposure, and faecal PCR indicates viral shedding. The likelihood of FIP is assessed from symptoms and samples suited to that purpose.
Can a cat recover from FIP?
Yes. Modern antiviral medicines have changed the prognosis, and many cats recover. Treatment and check-ups are planned with the vet, and recovery cannot be promised for every cat.
Must a cat with FIP always have abdominal fluid?
No. The disease can occur without fluid accumulation, and organ, eye or neurological signs may predominate. Features of the wet and dry forms may also occur together.
Can antiviral medication be stopped once my cat seems brighter?
Not on your own initiative. Recovery is assessed through clinical examination and monitoring results. The duration and end of treatment are decided individually.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Guideline for Feline Infectious Peritonitis, European Advisory Board on Cat Diseases, accessed 2026-11-03.
- Feline Infectious Peritonitis, Cornell Feline Health Centre, accessed 2026-11-03.
- Feline Infectious Peritonitis, ASPCApro, accessed 2026-11-03.
- Feline Infectious Peritonitis, Merck Veterinary Manual, accessed 2026-11-03.
- 2024 guidelines for the vaccination of dogs and cats, World Small Animal Veterinary Association, accessed 2026-11-03.
- 2022 ISFM Consensus Guidelines on Management of the Inappetent Hospitalised Cat, Journal of Feline Medicine and Surgery, accessed 2026-11-03.
- Clinical and clinicopathologic features of an undifferentiated resolving uveitis in kittens similar to that seen with feline infectious peritonitis, Journal of the American Veterinary Medical Association, accessed 2026-11-03.
- Feline Enteric Coronavirus Infection, Merck Veterinary Manual, accessed 2026-11-03.
- Initial Triage and Resuscitation of Small Animal Emergency Patients, Merck Veterinary Manual, accessed 2026-11-03.