Understanding This Serious Feline Disease

Feline Infectious Peritonitis (FIP) is a serious viral disease that can affect cats. It develops when a common virus called feline coronavirus (FCoV) mutates inside a cat’s body, triggering an abnormal immune response.

Many cats encounter feline coronavirus during their lives. In most cases, the virus causes mild digestive symptoms or no noticeable illness. Only a small percentage of cats experience the viral mutation associated with FIP.

For many years, FIP was considered one of the most challenging conditions in feline medicine. Today, veterinary medicine continues to explore improved diagnostic approaches and antiviral therapies that veterinarians may consider as part of an individualized care plan.

Understanding how FIP develops, which cats may have higher risk, and how veterinarians approach diagnosis and medical management can help cat owners work more closely with their veterinary team.

Important: The information on this page is provided for educational purposes only and should not replace guidance from a licensed veterinarian. Diagnosis and medical decisions for feline infectious peritonitis should always be made in consultation with a veterinary professional.

What Causes Feline Infectious Peritonitis in Cats?

Feline Infectious Peritonitis originates from feline coronavirus (FCoV), a virus commonly found in domestic cats. Many cats become infected with FCoV at some point in their lives, often without serious illness.

In some cats, the virus undergoes a mutation inside the body. When this occurs, the virus can enter certain immune cells and spread through the bloodstream, triggering inflammation in different tissues and organs.

Because the disease develops from a mutation that occurs within the individual cat, FIP itself is generally not considered contagious between cats, even though feline coronavirus can spread between animals.

Which Cats May Have Higher Risk for FIP?

FIP can occur in cats of any age, but certain factors appear to increase the likelihood that the viral mutation may occur.

Cats that may have a higher risk include:

Young cats under two years of age
Cats living in multi-cat environments such as shelters, breeding facilities, or rescue groups
Cats experiencing immune system stress
Certain purebred cats that may have genetic susceptibility

Even when these factors are present, most cats exposed to feline coronavirus do not develop FIP.

Common Symptoms of FIP in Cats

Signs of feline infectious peritonitis can vary depending on the form of the disease and the organs affected. Some symptoms may develop gradually, while others may appear more rapidly.

Possible signs veterinarians may evaluate include:

Persistent fever that does not respond to antibiotics
Loss of appetite
Weight loss
Lethargy
Abdominal swelling or fluid accumulation
Difficulty breathing
Eye inflammation
Neurological changes such as tremors or difficulty walking

Any cat showing these symptoms should be evaluated by a veterinarian as soon as possible.

Types of Feline Infectious Peritonitis

Veterinarians commonly classify FIP into two primary forms, although some cats may show characteristics of both forms as the disease progresses.

Wet (Effusive) FIP

Wet FIP is associated with fluid accumulation in body cavities, most often the abdomen or chest. This fluid buildup can cause visible swelling and may affect breathing.

Possible signs may include:

Abdominal distension
Difficulty breathing
Lethargy
Reduced appetite
Fever that does not respond to antibiotics

Cats showing these symptoms should receive veterinary evaluation as soon as possible.

Dry (Non-Effusive) FIP

Dry FIP does not involve the same fluid buildup seen in the wet form. Instead, inflammatory lesions may develop in organs such as the liver, kidneys, brain, or eyes.

Signs can vary depending on which organs are involved and may include:

Weight loss
Persistent fever
Eye inflammation
Neurological changes such as difficulty walking or tremors
Behavioral changes

Because symptoms can vary widely, dry FIP may sometimes be more difficult for veterinarians to confirm.

How Veterinarians Evaluate Possible FIP

Diagnosing FIP can be challenging because there is no single test that confirms the disease in every situation.

Veterinarians typically evaluate several pieces of information together, including:

Clinical symptoms
Blood test findings
Imaging studies such as ultrasound or X-rays
Analysis of fluid samples when fluid is present
Specialized laboratory testing

By combining these findings, veterinarians determine whether FIP is the most likely explanation for a cat’s condition.

Veterinary Management Approaches for FIP

Historically, medical management of FIP focused primarily on supportive care. In recent years, veterinary medicine has explored antiviral compounds designed to interfere with viral replication.

Veterinarians may consider these medications alongside supportive care measures depending on the individual cat’s condition.

Medical management decisions may depend on several factors, including:

The form of FIP present
The cat’s overall health
Neurological or ocular involvement
Response to veterinary care over time

Because FIP management can be complex, care plans should always be determined by a licensed veterinarian.

Role of Compounding Pharmacies in Veterinary Care

In some situations, veterinarians may prescribe medications that are not available in commercially manufactured forms suitable for a particular feline patient. Veterinary compounding pharmacies can prepare customized medications according to a veterinarian’s prescription.

Compounded medications may allow veterinarians to:

Adjust dosage strengths
Prepare medications in specific delivery forms
Customize formulations for an individual animal
Provide medication options when commercial products are unavailable

These customized preparations may help veterinarians tailor medical management plans to the specific needs of a feline patient.

Veterinary Compounding Support From ScriptWorks

ScriptWorks is an ACHC- and PCAB-accredited compounding pharmacy that prepares customized medications based on prescriptions from licensed healthcare providers, including veterinarians.

When a veterinarian determines that a compounded medication may be appropriate for a feline patient, our pharmacists prepare the formulation according to the prescriber’s specifications while following strict quality and safety standards.

If your cat is showing signs of illness, contact your veterinarian for evaluation and guidance. A veterinary professional can determine appropriate diagnostic testing and discuss possible care options.

This page is intended for educational and informational purposes only. It is not intended to replace professional veterinary advice, diagnosis, or medical care. Always consult a licensed veterinarian regarding the health and medical needs of your pet.

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