Feline infectious peritonitis (FIP)

FIP is a severe disease caused by feline coronavirus. Feline coronavirus is commonly found in the feces of cats and usually causes minimal signs. However, in a small number of cases, the virus mutates and can result in FIP. FIP is more common in pedigree cats, young cats and those in multi-cat households. FIP used to be a universally fatal disease, however recently new medications have been developed (available in the UK) and their success rate is high with around 85% of cats responding to treatment.

©Kim Willoughby

The disease is caused by a virus, feline coronavirus (FCoV), which is often found in the feces of healthy cats and usually causes no major health problems. However, in some cats it causes serious disease when the virus mutates.

The disease has four different forms:

• The most common form is called ‘wet ‘ or ‘effusive’ FIP; in this form, blood vessels leak protein-rich fluid into body cavities. Most commonly this fluid accumulates in the abdomen, causing it to swell leading to a ‘pregnant’ appearance. Fluid accumulation may also occur in the chest, causing life-threatening breathing problems.
• The less common forms of the disease include ‘dry’ or ‘non-effusive’ FIP in which inflammatory nodules develop in the cat’s internal organs and can cause a wide variety of clinical signs.
• Ocular FIP can also occur, whereby the eyes are affected.
• Neurological FIP results in neurological signs, such as seizures.

FIP does not spread between cats but FCoV, that can trigger disease, is highly infectious. Infection with FCoV is very common, particularly in cats from rescue shelters, breeding catteries and other large multi-cat households. FCoV is mostly spread in feces (droppings/poo) but can also be found in saliva. FIP develops as a result of viral mutations within individual cats.

The greater the viral burden within a household and the greater the viral turnover within an individual cat, the more likely that FIP with occur. Only about one in a hundred cats is likely to go down with the disease but the risk is much higher where several cats live together such as in a breeding cattery or rescue center. Overcrowding and other stressful factors can increase the risk of disease developing.

The most vulnerable cats are those with weak defenses against infectious diseases, eg kittens, elderly cats and those already suffering from some other condition. Some pedigree breeds, eg Birman, Ragdoll, Bengals and Rexes, appear to be affected more often than the ordinary domestic ‘moggy’ in some studies.

In the early stages of disease, FIP can cause a variety of clinical signs such as weight loss, lethargy, a dull coat, diarrhea, poor appetite and fever. These signs may or may not be present and are also common to many other diseases, so early diagnosis can be challenging. In cats with the ‘wet’ form of FIP, fluid may build up in your cat’s abdomen (causing swelling of the tummy) or chest (causing difficulty in breathing). In cats with the ‘dry’ form of FIP, your cat’s eyes or nervous system may be damaged causing a change in the color of the eye, blindness, wobbliness when walking, tremors and even seizures.

There is no reliable blood test to show that your cat has FIP. Blood tests may show high protein levels and low red blood cells. There may also be increased bilirubin (which can result in jaundice) and an increase in markers of inflammation. Imaging the chest and abdomen is recommended to look for fluid, enlarged lymph nodes and abnormal organs. Where fluid has built up in the chest or abdomen this can be sampled and analyzed. In some cases, these laboratory results can give a strong suggestion of FIP or even confirm infection. In many cases the only sure method of diagnosis is to take a tissue sample from one of the internal organs. Such invasive sampling may cause discomfort and can be costly. Tissue sampling is unfortunately often done only after the cat has died and can then confirm FIP as the cause of death.

There is no evidence that FIP can cause any disease in humans or other animals such as dogs. Rarely it can affect big cats such as cheetahs in zoos or in the wild.

There are now three medications that can be used to treat FIP. The most commonly used are remdesivir and GS-441524. In acutely ill cats who cannot take oral medication, then remdesivir is given by injection. GS-441524 can be given orally, either as a tablet or liquid, and is usually the preferred treatment. For cases that are not responding to treatment then a third medication called EIDD-1931 can be trialed. Studies looking at remdesivir and GS-4451524 show that around 85% of cats will show a positive response to treatment.

Current recommendations are to treat patients for 12 weeks. The different types of FIP require different doses of the above anti-viral drugs, with neurological FIP requiring the highest doses.

The causative virus (FCoV) is spread in saliva, phlegm and in feces. Most cats that contract the virus are able to clear the infection. Some of these cats may continue to carry the virus and are a source of infection for other cats. If a cat with FIP is already living with other cats, then there is no need to isolate the affected cat as the other cats are already likely to have been exposed to the coronavirus. However, you should avoid bringing new cats into the household.

The virus only survives a couple of months outside the cat, and it can be killed using a dilute solution of household bleach (about five tablespoons of bleach in a gallon of water). Use this to clean the feeding bowls, litter trays etc. and to wipe down room surfaces. Remember that this is caustic – so wear gloves, skin and eye protection. Ensure that surfaces are rinsed clean before allowing the cat to contact them.

An FIP vaccine has been developed in the US and some parts of Europe. Veterinarians disagree on how effective it is in preventing FIP, and it is not currently recommended by feline specialists.