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FIP is a chronic disease that turns fatal when the cat's immune system is damaged or overwhelmed by too many challenges. When a cat is exposed to FIPV it can usually neutralise the virus but doesn't completely clear the infection. Instead, the virus probably remains latent or inactivated in the bone marrow or some other organ. When the cat's defences are destroyed and T-cell numbers dwindle, the virus is able to replicate again and attack the tissues. If blood cells are destroyed, the cat will be prone to bacterial, viral, and fungal infections, or anemia. In some cases, these infections are recurrent but since the symptoms are not pathognomic the cat is treated palliatively with drugs that harm the cat but don't affect the virus. As a result, the cat is weakened and cannot mount an immune response to the disease.


When kittens are taken to the vet with fever, URIs, diarrhoea, etc., they are usually given antibiotics, which only weaken the immune system even more and destroy the beneficial bacteria in the gut. Vets don't usually consider FIP because there is no simple way to test for it, so the disease is overlooked at this stage, and indeed it is possibly the most underdiagnosed disease in cats, before the terminal stage. 


​Apart from genetics, the single most important predisposing factor for FIP is stress. When a cat is stressed it produces cortisol which destroys the part of the immune system that is able to neutralise the FIP virus in the bloodstream. If you minimise and spread out stressors, the cat’s immune system is able to recoup and mount a robust immune response, and so prevent the virus from spreading to the rest of the body.

Some of the things that a cat perceives as stress:

  • Changes in routine, moving house, new people or animals, fights with other cats, visits to the vet. Some cats enjoy travelling in a car or meeting new people, but these are probably a very small minority and most cats get very stressed when they are taken out of their familiar surroundings.

  • Sterilisation before maturity. This will be necessary in my opinion as long as cat overpopulation persists in our societies. Since it has to be done, my advice is not to neuter cats that have recently been vaccinated so that the cat’s immune system has enough time to recoup. You can read a well-balanced article here.

  • Overvaccination, and particularly multivalent vaccines. The risks and putative benefits of vaccines have been described often enough, so I just want to stress that multiple vaccinations on the same day and unnecessary boosters can overwhelm the cat’s immune system, resulting in inadequate immunity and an increased risk of adverse reactions. 

  • Forcible weaning. Cats suckle their kittens for 3 months or more and gradually wean them off. This is a vital part of a cat’s life in which it learns how to hunt, how to behave with other cats, and how to stand up for itself. Taking kittens from their mother before they are ready to face the world damages their immune system in the short term, and later on in life as the cat lacks the confidence to interact with its environment. A scaredy cat is continually stressed by everyday situations and its immune system will be unable to cope with disease.

  • Gut health. I cannot find any research backing the claims made by grain-free food acolytes. Whilst some carbohydrates are to be avoided, a moderate amount of fermentable, non-abrasive fibre like rice or corn is necessary for optimal gut health, and hence for an adequate immune response to pathogens. If beneficial and commensal microorganisms don’t get some fermentable fibre as fuel for cell metabolism, their numbers dwindle and facultative pathogens are able to gain a foothold.

Grain-free food substitutes vegetables that alkalise the enteric environment and the urine, causing disruption to the gut ecology and increasing the risk of struvite crystals in the bladder. (In this respect, the gut microflora also contributes to a process known as colonic dialysis which takes some of the load off the kidneys and is especially important for CKD cats.)

Additionally, most vegetables, fruits and herbs are toxic for cats because their liver cannot conjugate the complex plant molecules. Compared to pack hunters like wolves and wild dogs, cats have very simple, light livers that give them an evolutionary edge when they pounce on a mouse, but are unable to detoxify complex molecules like saponins, phenols, terpenes and benzyl alkaloids among other toxins.

According to recent research in cats —not dogs or humans, who have different gut ecologies and different nutritional needs— corn and rice are easily digested by cats and have no deleterious effect on the gastrointestinal tract or kidneys. In the case of FIP, adding finely ground rice bran and cooked pumpkin to the cat’s diet fosters an optimal gut environment.

  • Raw food. Beneficial bacteria are also necessary to manufacture micronutrients that cats —as obligate carnivores— cannot get from plants directly. When a cat eats a freshly-killed bird or mouse it benefits from the prey's nutritious blood and gut contents. Among other nutrients, cats cannot synthesise carotene, and neither can they get it from meat, bones and organs alone: cats get retinol from meat but they cannot convert vitamin A to carotene in any significant amounts because they lack the necessary enzyme (dioxygenase). Cats need much more carotene than dogs (about twelve times more) and this is essential to cell-mediated and humoral immunity. Cats get β-carotene from prey gut contents with the help of beneficial bacteria and release it for absorption by immune cells. Adding cooked pumpkin and gem squash to their diet provides carotene in sufficient amounts for optimal gut heath and correct functioning of the immune system.

  • Spaced-out meals. Cats in the wild eat several times a day and additionally snack on protein-rich crickets and grasshoppers. Probably because smaller species have a faster metabolism, cats need to eat every three hours or so in order to prevent kidney damage. If the cat is starved between meals it starts feeding on its own muscle, so providing a high-protein kibble that has no toxins is essential for a cat's overall health. Kibble has a similar water content as insects that are part of a cat's natural diet, and as long as a cat is getting all the nutrients it needs from a balanced diet it will not overeat. Exercise and interactive toys that allow the cat to 'hunt' their food are great ways to keep your cat healthy and trim.

  • Although corticosteroids are often prescribed for FIP-related inflammation, they have the effect of destroying the cat's lymphocytes that are part of the cell-mediated immune response in most infections. Antibiotics and dewormers also of course cause enteric dysbiosis and should not be overused.

FIP is mainly a disease of catteries and shelters. Incorrect breeding protocols, inbreeding and a poor understanding of genetics is often causative of the disease. The iCatCare website has some recommendations for breeding catteries: 

FIP is least common in household pets. The risk can be minimised by obtaining cats from a source with relatively few cats and by keeping cats in small stable groups (less than five cats in a household).

In breeding catteries, eradicating coronavirus infections is extremely difficult, as the virus is so ubiquitous, and it is unsuitable in most situations to attempt this. A more practical approach is to use measures to reduce the risk of FIP occurring, but recognising that on occasions, this may happen even in the best run catteries. Good practice to minimise the risk of FIP would include:

  • Avoid keeping large groups of cats and having multiple litters of kittens at any one time

  • Keep cats in small isolated groups (ideally no more than four cats in each group - this reduces the risk of endemic FCoV infection)

  • Have at least one litter box for every two cats, located in easy to clean and disinfect areas

  • Keep litterboxes away from food and water bowls, and clean/disinfect them regularly (at least daily)

  • Avoid stress and maintain good hygiene and preventive healthcare for all cats

Wherever FIP occurs is a problem in a group of breeding cats:

  • Consider preferentially breeding from older cats, as these will less likely be shedding FCoV

  • Consider isolating queens just before they give birth and keeping the queen and kittens isolated from all other cats until the kittens are homed, as a means of reducing the risk of FCoV spread to kittens

  • Stop breeding from any queens or tom cats that repeatedly produce litters of kittens that develop FIP as they may be passing on FCoV infection or may be passing on genetic susceptibility to disease

  • Carefully review management and hygiene policies

  • If faced with an outbreak of FIP, stop all breeding for several months

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