How Do Cats Get FIP? Understanding Feline Infectious Peritonitis

Feline Infectious Peritonitis (FIP) is a challenging disease to diagnose and treat, affecting even fully vaccinated indoor cats. Most cats come into contact with a common virus known as feline coronavirus (FCoV) at some point, but only a small number develop FIP. The key factor in whether a cat develops FIP is how its immune system responds to the virus.

The issue arises when a cat's immune system overreacts to the coronavirus, causing harmful inflammation. This immune overreaction is what leads to the symptoms of FIP. Cats with genetic similarities, such as related cats, may be more at risk due to their immune system traits.

How Cats Contract FIP

The feline coronavirus commonly infects the intestines and often causes no or mild symptoms like a brief bout of diarrhoea. Cats contract the virus mainly through contact with infected faeces, sharing litter trays, grooming, or close interaction with other cats. The virus may also spread from mother cats to their kittens, sometimes even before birth.

In a minority of cats – about 5-10% – the virus mutates inside the cat’s body into a form that infects blood cells and triggers a systemic immune response, leading to FIP. Young cats under two years, older cats, and those under stress or in crowded environments are more susceptible. Good hygiene and lower numbers of cats in a household reduce the risk.

Should Cats with FIP Be Separated?

Because feline coronavirus spreads through faeces and grooming, vets often advise isolating a suspected FIP cat from others in multi-cat households, providing separate litter trays and feeding areas. However, if other cats show no symptoms or immune reaction to the virus, strict separation might not always be necessary. Occasionally, symptoms similar to FIP could be due to genetic kidney diseases unrelated to the virus.

The Two Forms of FIP

FIP manifests in two main forms: the "wet" (effusive) form, characterised by fluid build-up in the abdomen or chest, and the "dry" (non-effusive) form, where symptoms are less obvious but affect organs internally. Both forms result from the same virus mutation.

Currently, no effective vaccine exists to prevent FIP. Most cats exposed to feline coronavirus recover after mild illness without developing FIP.

Recognising FIP Symptoms

Early symptoms can be subtle and mimic other illnesses, making diagnosis difficult. Watch for:

• Slight fluctuating fever
• Lethargy and tiredness
• Loss of appetite
• Abdominal or chest swelling due to fluid
• Difficulty breathing

Veterinary diagnosis often requires advanced testing and sometimes post-mortem examination due to symptom overlap with other diseases.

Treatment and Care

No cure for FIP currently exists. Veterinary care focuses on supportive treatment to ease symptoms, such as anti-inflammatory medications to improve quality of life. In advanced cases where suffering occurs, humane euthanasia may be recommended.

Preventing FIP

Prevention centres on reducing virus spread and stress in cats:

• Limit household cat numbers to reduce virus circulation—ideally no more than four.
• Keep litter trays clean and disinfected daily, placing them away from food and water bowls.
• Provide each cat with their own litter tray to avoid cross-contamination.
• Maintain a hygienic and low-stress environment for cats.

Summary

Although most cats encounter feline coronavirus, only a few develop FIP due to a unique mutation in the virus combined with an individual cat's immune response. Recognising early symptoms, practising excellent hygiene, and limiting overcrowding can help reduce FIP risk. If you suspect your cat may have FIP, consult a vet promptly for assessment and supportive care options.