Feline Infectious Peritonitis

This blog post comes following some sad news this week. One of our cats that had been adopted a couple of months ago, passed away under general anaesthetic during a routine desexing operation.

We were absolutely devastated to hear this news, and extend our deepest sympathies to her beautiful foster family.

The veterinarians that were performing her procedure suspect she may have been suffering from feline infectious peritonitis (FIP).

Whilst FIP is relatively rare, it is a very serious disease with a 100% mortality rate, no effective treatment or cure, and is extremely difficult to definitively diagnose.

FIP is commonly referred to as the silent killer because cats often don’t show any clinical signs until very late in the course of the disease, as was the case for the beautiful kitten we lost recently.

So what causes FIP?

The virus that causes FIP is actually CORONAVIRUS!

While coronavirus is a ‘new’ virus to many, we have been dealing with it for years and years in the veterinary industry! Please do not get confused though – the coronavirus that causes FIP in cats, is very different to the current pandemic-causing coronavirus (COVID-19).

The thought of people in this world not understanding the extent of how serious the coronavirus pandemic is OR that the pandemic isn’t even real, is very frustrating for me when we see coronavirus infections so often in veterinary medicine, not to mention how scary it can be if these viruses mutate. I’ll explain more about the mutation of the virus below!

It is not uncommon for young kittens to become infected with coronavirus. The coronavirus that infects kittens is called an enteric coronavirus, meaning that the virus focuses on the gastrointestinal tract,and most kittens only experience symptoms such as fever, lethargy and diarrhea. Occasionally they can also experience sneezing, watery eyes, and nasal discharge. It is transmitted by close contact with other infected cats faeces (sharing litter trays, cats housed in groups, etc.)

Once infected, symptoms and shedding of the virus (i.e. when they are contagious to other cats) can last for several weeks! Because this virus loves to circulate between cats living in households together, some cats in households with more than 5 cats may see frequent re-infections.

So why don’t more cats become infected with FIP, if coronavirus is not an uncommon virus in cats?

Many cats infected with coronavirus won’t progress to FIP. In rare cases however (i.e. those that progress to having FIP), the virus will mutate at just the right time. While the immune system is frantically trying to remove coronavirus from the infected individuals gastrointestinal tract via specialized cells called macrophages that eat up all infected material within the body, the virus undergoes a mutation within the cell.

The mutation allows the virus to survive within the macrophage cells, and essentially hijacks these cells. The virus is then able to spread to other areas of the body. As the body tries to kill the infected macrophages, a major immunologic dysfunction occurs, which then leads to organ dysfunction, and in some forms of the disease, fluid build up in the chest or abdomen.

What are the symptoms of FIP?

Following infection with coronavirus, it can take weeks, months or even years for FIP signs to develop.

Initially most cats show non-specific signs such as lethargy, decreased appetite, weight loss and fever. Most of these initial signs are very subtle, and often owners don’t even see these signs, due to cats being very good at disguising signs of illness. They are well known to be the masters of disguise!

In the later stages of the disease, FIP can take on two forms, wet (effusive) and dry (non-effusive).

The wet form often presents in the later stage with fluid accumulation in the abdomen and/or chest.

The dry form tends to progress more slowly, and signs are subtler due to deep inflammation within the nervous system and eyes. The dry form tends to cause more neurological signs in the end stages, such as seizures.

As I mentioned earlier, cats are remarkably good at hiding signs of disease. In my experience, owners sometimes blame themselves for not seeing signs earlier when we find they have a large accumulation of fluid in their chest or abdomen. Or in the case of one of our adopted cats recently, they seem perfectly fine right up until they undergo a stressful event, such as a routine desexing.

I always remind owners that unfortunately cats are masters at hiding signs of illness, and will continue to hide them from their family right up until the end.

Why isn’t there a test available for definitive diagnosis of FIP?

While there is a test for coronavirus, there isn’t a test available to diagnose FIP. This is due to the mutation that occurs to the virus, leading to FIP in some individuals. The mutations are random, and there are too many different mutations that occur to be able to diagnose them all on one test.

If your veterinarian suspects your cat may have FIP, a number of preliminary tests can be performed. These are not definitive tests, however the veterinarian may be able to make assumptions based off a number of findings.

These tests may involve:

  • Blood tests to check protein levels
  • Tests to check if the cat has previously been infected with coronavirus
  • Testing fluid that has been drawn off the chest and/or abdomen if present
  • Surgical biopsy (however most kittens are too unwell for surgery by this stage)

So if there is no treatment, can we do anything for palliation?

Unfortunately there is currently no cure for FIP.

There are palliation drugs available, such as medications that suppress the immune system, however nothing has proven to be very effective so far.

What increases the risk of coronavirus mutation within a cat?

Risk factors that have been associated with increased chances of mutation within a cat infected with coronavirus include:

  • Immune suppression/stress
  • Overcrowding conditions (i.e. more than 5 cats in a household) and in breeding catteries
  • Shared litter trays
  • Genetics
  • Early weaning from the mother cat

Should I be concerned if one of my cats is diagnosed with FIP – will any of my other pets catch the disease?

It is likely that the other cat has been infected with coronavirus, as coronavirus is contagious. The mutated form (FIP) is not contagious. Littermates may have an increased risk of developing FIP due to genetics, however it cannot be passed on to other cats.

It is also species specific, so cannot be passed onto humans, dogs, etc.

RIP Lily

April 2020 – October 2020

Please feel free to leave any questions you may have in the comments.

Feline Idiopathic Cystitis

Also known as:

  • Stress cystitis
  • Feline interstitial cystitis
  • Pandora syndrome
  • Idiopathic feline lower urinary tract disease (FLUTD)

This is my favourite disease of all time to educate clients about!

Whilst it can be a very frustrating disease, with some patients experiencing recurrent bouts of FIC throughout their lifetime, there are many different options for management and treatment.

Environmental modification and enrichment has been shown to reduce the frequency and severity of clinical signs by 70-80%, which in my opinion is pretty outstanding! Just by improving your cats home environment, it is likely you can effectively manage this disease for the rest of their lives with very minimal long term costs.

This post is just an overview of the fascinating topic of feline idiopathic cystitis, and treatment options will be elaborated on in future posts – so stay tuned!


Feline idiopathic cystitis is a chronic sterile inflammation of the bladder. Although they may show symptoms of having a urinary tract infection, there is no infectious component (i.e. bacteria) contributing to the bladder inflammation.

Studies have shown that in young cats showing urinary tract symptoms, less than 2% will actually have a true urinary tract infection.

It is likely that there are multiple factors that lead to sterile inflammation of the bladder including interactions between the bladder wall, the nervous system, the adrenal glands and the environment.

Symptoms may include:

  • Increased frequency and/or urgency of urination
  • Straining to urinate
  • Urinating in unusual places (towels, sheets, sinks, showers)
  • Excessive grooming
  • Blood in the urine
  • Behavior changes (aggression, hiding)
  • Distressed crying (while urinating or near the litter tray)

FIC can be classified into ‘obstructive’ or ‘non-obstructive’

Non-obstructive FIC occurs in approximately 80-95% of cases, and symptoms will usually resolve within 1-2 weeks

Obstructive FIC occurs in approximately 15-25% of cases. Obstructive FIC causes the urine to be unable to drain from the bladder. This is a potentially life-threatening condition, and symptoms include, in addition to those listed above, lethargy, vomiting and/or inappetance. Obstructive FIC predominantly occurs in male cats due to their narrow urethra, however can still occur in female cats.

Diagnosis of FIC:

FIC is a diagnosis of exclusion, meaning all other causes of urinary tract inflammation must be ruled out. Other causes of lower urinary tract signs include a urinary tract infection, urine crystals and bladder cancer.

First, your veterinarian will need to evaluate a urine sample from your cat. Ideally, the urine sample is retrieved via a short procedure called cystocentesis. This procedure is performed by inserting a small needle through the skin and into the bladder. The urine sample is sent to an external laboratory for comprehensive testing. Your veterinarian may also request blood tests.

Risk factors for FIC:

Some cats are more prone to FIC. As stated above, this is usually a combination of factors including genetics and the environment.

Cats that are more at risk of developing FIC include:

  • Male cats (especially neutered males)
  • Overweight cats and sedentary cats, with very little exercise
  • Cats in multi-cat household, particularly when there is tension between cats
  • Cats in a new or different environment to their usual routine
  • Cats that eat mainly dry food or cat biscuits (leading to inadequate water intake)
  • Cats that do not have adequate number or size litter trays


There is currently no cure for FIC, and due to the waxing and waning nature of the disease, goals of therapy are to reduce the severity and duration of clinical signs. Treatment also aims to prolong the time between FIC episodes in cats that experience recurrent FIC.

Treatment includes a multi-modal response, including:

  1. Environmental modification to reduce stress
  • Multiple and separate resources such as food and litter trays (particularly in multi-cat households)
  • Hiding places and high viewing points
  • Increased play, exercise and human-cat interaction
  • Outdoor runs and enclosures
  1. Increasing water intake and diet management
  • Low calorie weight loss diets
  • Specific urinary health diets
  • Pet fountains to promote drinking water
  • Increasing wet food component of diet
  1. Litter tray management
  • Increasing the number and locations of litter trays in the house – particularly in multi-cat households (one litter tray per cat PLUS one)
  • Regular cleaning
  • Trialing different types of litter – your cat may have a preference!
  • Increasing the size of the tray
  1. Use of medications (over the counter and prescription from your veterinarian)

I always recommend an examination by a veterinarian each time your cat has a recurrence of FIC to ensure that they are not experiencing a life-threatening urinary obstruction. By working with your veterinarian, the aim is to reduce the severity of symptoms during a FIC flare up, and reduce the frequency of recurrence long term.