What Is Feline Infectious Peritonitis (FIP)?

Feline Infectious Peritonitis, commonly known as FIP, is a serious viral disease that affects cats. It develops from a mutation of the feline coronavirus (FCoV), a common virus found in cats, especially those living in multi-cat environments such as shelters or catteries.

While many cats infected with feline coronavirus remain healthy or experience only mild digestive symptoms, in some cats the virus mutates and causes FIP, leading to severe inflammation throughout the body.

FIP was once considered almost always fatal, but recent advances in veterinary medicine have significantly improved treatment outcomes.

What Causes FIP?

FIP occurs when the feline coronavirus mutates inside a cat’s body and triggers an abnormal immune response. The disease is not usually spread directly as FIP itself; instead, cats spread the common feline coronavirus through:

  • Feces
  • Shared litter boxes
  • Food and water bowls
  • Close contact with infected cats

Young cats under two years old, senior cats, and cats with weakened immune systems are more vulnerable.

Types of FIP

1. Wet (Effusive) FIP

This form causes fluid buildup in the abdomen or chest.

Common signs include:

  • Swollen belly
  • Difficulty breathing
  • Fever
  • Weight loss
  • Loss of appetite

2. Dry (Non-Effusive) FIP

This form affects organs such as the eyes, brain, kidneys, or liver.

Symptoms may include:

  • Neurological problems
  • Eye inflammation
  • Poor coordination
  • Chronic fever
  • Weight loss

Symptoms of FIP in Cats

The symptoms of FIP can vary depending on the type and severity of the disease. Common signs include:

  • Persistent fever that does not respond to antibiotics
  • Loss of appetite
  • Weight loss
  • Lethargy
  • Swollen abdomen
  • Breathing difficulties
  • Jaundice
  • Eye changes
  • Neurological symptoms such as seizures or imbalance

If you notice these signs, immediate veterinary attention is essential.

How Is FIP Diagnosed?

Diagnosing FIP can be challenging because its symptoms resemble many other diseases. Veterinarians may use:

  • Physical examination
  • Blood tests
  • Ultrasound or X-rays
  • Analysis of abdominal or chest fluid
  • PCR testing
  • Biopsy in some cases

No single test can confirm FIP with complete certainty, so diagnosis often involves evaluating multiple findings together.

Treatment Options for FIP

For many years, treatment options were limited. Today, antiviral medications such as GS-441524 have shown promising success in treating many cats with FIP under veterinary supervision.

Treatment may include:

  • Antiviral therapy
  • Supportive care
  • Nutritional support
  • Fluid management
  • Anti-inflammatory medications

Early diagnosis greatly improves the chances of successful treatment.

Can FIP Be Prevented?

While there is no guaranteed way to prevent FIP, these steps may reduce the risk:

  • Keep litter boxes clean
  • Avoid overcrowding cats
  • Reduce stress in multi-cat households
  • Isolate sick cats when necessary
  • Maintain regular veterinary checkups

When to See a Veterinarian

Contact your veterinarian immediately if your cat shows:

  • Persistent fever
  • Rapid weight loss
  • Swollen abdomen
  • Difficulty breathing
  • Sudden neurological symptoms

Early medical intervention can make a major difference in treatment success.

Final Thoughts

Feline Infectious Peritonitis is a complex and serious disease, but advances in veterinary medicine are giving many cats a better chance at recovery than ever before. Awareness of the symptoms and seeking prompt veterinary care are the best steps pet owners can take to protect their feline companions.