Feline Infectious Peritonitis (FIP) in Cats

Feline infectious peritonitis, usually called FIP, was once considered almost hopeless. In recent years, understanding and treatment options have changed a lot, but FIP is still a serious disease that requires a veterinarian's diagnosis and close monitoring. Understanding it properly helps you spot it early and avoid unnecessary panic.

Where FIP comes from

• Feline coronavirus is very common, especially where many cats live together. Most infected cats have only mild diarrhea or no symptoms at all.
• In a small number of cats, the virus changes inside the body and behaves differently, causing widespread inflammation. That's when a cat develops FIP.
• The intestinal virus spreads through feces and shared litter boxes; the mutated form that causes FIP is generally not considered to pass easily from cat to cat.
• It's most common in young cats, usually under about two years old, cats in crowded groups, stressed cats and cats with weakened immune systems. Older cats can also be affected.

Feline coronavirus is different from the coronaviruses that cause disease in people. FIP does not spread to humans.

Signs of the disease

General signs

• Persistent fever that doesn't improve with antibiotics.
• Poor appetite, weight loss, slow growth in kittens.
• Lethargy and a scruffy coat.

Wet form

• A gradually swelling, distended belly from fluid in the abdomen.
• Rapid or labored breathing if fluid builds up in the chest.
• Possible yellowing of the gums and skin.

Dry form

• Inflammation in multiple organs such as the liver, kidneys and lymph nodes.
• Eye changes: cloudiness, color change, blood in the eye.
• Neurological signs: wobbliness, seizures, behavior changes.

Many cats show a mix of both forms, and the signs can resemble many other diseases.

Diagnosis and treatment

No single simple test confirms FIP in every case. Veterinarians usually combine:

• History, age, living environment and symptoms.
• Blood tests and analysis of abdominal or chest fluid, if present.
• Ultrasound and X-rays.
• Tests that detect the virus's genetic material in fluid or tissue.

A positive coronavirus antibody test does not mean a cat has FIP, because many healthy cats have antibodies too.

Treatment and care

• In many places, antiviral treatments are now available that have helped many cats recover. Treatment courses are usually long and need to be prescribed, monitored with follow-up tests and adjusted by a veterinarian. Availability and regulations for these medicines vary by location.
• Don't buy medicines of unknown origin or composition online. Incorrect use can lead to drug resistance, relapse or dangerous side effects.
• Cats that have recovered still need follow-up visits on schedule so any relapse is caught early.
• Supportive care at home matters a lot: keep your cat warm, provide a quiet resting place and easy-to-eat food, track weight, and record temperature and appetite as your vet instructs.

Reducing the risk of FIP

• Don't keep too many cats in a cramped space.
• Provide enough litter boxes (commonly one more than the number of cats), scoop daily and keep them away from food.
• Reduce stress: a stable environment, plenty of hiding places and few sudden changes.
• Keep newly adopted cats separate and have them checked before joining the group.
• Keep up health checks, core vaccinations and parasite prevention on your veterinarian's schedule.

When to see a vet

• Persistent fever, poor appetite or unexplained weight loss.
• A belly that swells quickly and feels tight.
• Rapid or open-mouth breathing: an emergency.
• Eyes that change color, become cloudy or show blood; staggering or seizures.
• Yellow gums or skin.
• A cat being treated for FIP gets worse or relapses after treatment ends.