Feline Infectious Peritonitis

16th Oct, 2023

Written by Dr Rowena Watson, Small Animal Medicine Resident, Johannesburg Specialist Veterinary Centre (JSVC)

For 60 years, feline infectious peritonitis (FIP) has been every cat owner’s worst fear. It can be challenging to diagnose, and until 2019, was uniformly fatal. Indeed, the saying was that if a cat lived after a diagnosis of FIP, the diagnosis was wrong. In 2019, the situation changed dramatically – and is still changing – bringing hope to all cat owners.

What is FIP?

FIP arises from a mutated version of Feline Corona Virus. Feline Corona Virus (FCoV) is a relatively harmless virus itself, which many cats are exposed to, especially in multiple cat households/situations (catteries, shelters, etc.). FCoV infects intestinal cells exclusively, and may cause mild, self-limiting gastro-intestinal signs.

However, corona viruses overall are prone to mutation, and certain mutations in the viral RNA enable the virus to leave the intestinal cells and infect macrophages, a component of the immune system. Even with this, however, disease is not a guarantee.

The final step in developing FIP is for the cat’s own immune system to fail. If a cat can mount an effective immune response, the virus can be eliminated; but if the immune system is somehow compromised, the response can be inappropriate, and the cat’s own immune system can drive inflammation and cause severe damage and disease. Although FCoV is highly contagious, the mutated version capable of causing disease can’t be transmitted.

Disease is most often seen in animals that already have compromised immune systems, including young cats and kittens, elderly cats, or cats with Feline Immunodeficiency Virus or Feline Leukaemia Virus. Often, disease is precipitated by a stressful event, such as rehoming or staying in a cattery – because stress can impact the immune system.

How do I know if my cat has FIP?

Clinical signs of FIP are extremely varied. The classical wet or effusive form is easiest to recognise and diagnose. This is characterised by a buildup of fluid in the abdomen or chest, which owners will notice as a distended belly or difficulty breathing. Many cats are lethargic and have a poor appetite and weight loss – but some cats may be in a hypermetabolic state, where despite fluid accumulation and weight loss, they continue eating.

Dry or non-effusive forms of FIP can present as a cat that’s just not right – lethargic and poor appetite and losing weight or might have changes in their eyes, with their eyes changing colour, or becoming cloudy. Some cats might have neurological disease, where they might become wobbly on their legs, struggle to walk, or even seizure. These forms are more difficult to diagnose, but suspicion can be raised by bloodwork, abdominal ultrasound and possibly MRI or CSF tap for neurological cases. Many cats have a combination of signs of both wet and dry FIP.

How is FIP treated?

Treatments for FIP have come an enormous way in the last five years, and our journey to get to where we are today, and the different treatment options, are a book in itself! Suffice to say, two different antiviral medications are currently available to treat FIP.

The first, most researched and the current gold standard of treatment is a medication called GS441-524 (or Remdesivir, which is the pro-drug, and is metabolised to GS). Trials with this medication were first published in 2019 and revolutionised the field. Currently, cure rates for FIP treated with GS are estimated at 90-95%. GS441-524 has taken a while to become commercially available but is luckily now easy to obtain. Although it’s still an expensive treatment, the prices have come down dramatically in the past four years.

The second medication has been used for a relatively short period and has only been available in South Africa from the beginning of 2023. This medication, called molnupiravir, is significantly cheaper than GS, but is still a relatively unknown entity. The long-term side effects are as yet unknown, and peer-reviewed, scientific data on efficacy are lacking. However, the cost of it makes it an attractive option. My personal experience with it has been extremely positive thus far.

Currently, a massive amount of research is being done into FIP. This entails everything from additional antivirals to combinations of treatments, to stem cell therapy and gene therapy to modulate the immune system. No doubt, the next five years will see even bigger and better changes in the field.

Testimonial Story:


Written by Elizabeth Pretorius

Photography by Vanessa Bentley Photography 

Our dearest little Chelsea girl came to live with us on the 25th of August 2021 at the age of three months, courtesy of the wonderful people at the Cluny Trust, who do really great work in the Free State.

Although hesitant, because we were in the process of saying goodbye to our Asjas, who’d previously been successfully treated for skin cancer on the nose by Dr Georgina Crewe (Dr Crewe does ground-breaking work on this in SA from her practice in Fairlands), we decided to apply for the adoption of Chels.

From the minute she arrived after her long car journey from Clarens and jumped out of her travel basket and onto my lap, she had us eating out of her little paw. She adored Max, her older “brother”, and accepted it gracefully when Jack also came to live with us, all the while, with her insatiable curiosity, discovering every nook and cranny of the house, garden and every other possible spot behind any closed door.

In July/August 2022, I was slightly concerned that she calmed down a bit too much for such a curious, lively little kitty, and I took her to our local vet. Nothing untoward stood out, but I made a booking again to have her seen to by the senior partner at Linden Vet on Monday, the 12
th of September. Dr Tanya Potgieter decided to run blood tests and found her to be anaemic and with increased levels of globulin. Both signs of the presence of either one of a few cancers or feline infectious peritonitis (FIP), which I’ve never heard of before.

We were referred to Johannesburg Specialist Veterinary Centre (JSVC) in Randparkridge on the 14
th of September, where she had an abdominal scan which revealed a large mass in the small intestine, with enlarged lymph nodes around it. The first available theatre slot with Dr Fanie Naude was on Tuesday, the 20th of September. He successfully removed a very large growth, with only a tiny opening allowing fluids through, and managed to find enough healthy tissue to join up the ends.

Chelsea remained in hospital for a week and was discharged on Friday, the 23rd of September at around lunchtime. She was so happy to be home but, in the early evening of the following day, she started growling at us when touching her stomach, and she looked really tired and felt very warm to the touch.

We took her to the 24-hour Fourways Veterinary Hospital and Specialist Referral Centre (FSVH) at about 21h30. She had a fever of 40.3°C and some inflammation around the skin wound and stitches. They also performed a quick scan to check on the intestinal operation wound and confirmed that it was all good. We again took her to JSV for a check-up on Sunday morning.

As there’s no conclusive test for FIP, we had pathologists trying to rule out possibilities. On Monday, the 26
th of September, we still had FIP as the strongest possibility; by Friday the 30th it looked 99.9 per cent sure to be small cell lymphoma and we, in fact, started with chemotherapy that Friday. Her stitches came out on Monday, the 3rd of October, because the wound healed really well but we had an ongoing issue with a slight fever subsiding and returning.

By this time, we had Dr Rowena Watson (JSV) explain FIP to us in detail, along with the fact that, for the first time since the discovery of this disease 70 years ago, treatment was available. As a result of the pandemic, an American veterinary surgeon, Dr Niels Pedersen, experimented with some treatment used for Covid 19 and found Remdesivir to be effective. Dr Watson researched treatments during lockdown as she had her own fur child diagnosed with FIP and treated her/him successfully. Thanks to her amazing work, the treatment became available in South Africa. The fact isn’t widely known, though – hence our post and campaign to get more people and vets aware.

Summarising FIP as we came to understand it, is the following: cats are carriers of the feline corona virus and, as a rule, don’t get sick from it. Cats in catteries, colonies, etc. are sure to have it. If in an individual, with a compromised immune system (often kittens but also older cats) at a given time, the virus escapes and mutates at least twice, FIP is the result. A perfect storm is needed, as Dr Rowena explained it. Low immunity, plus same-time escape, plus more than one mutation. FIP is the result, and there are two versions: intestinal (or wet) FIP or neurological (dry) FIP.

In wet FIP, straw-yellow sticky fluid forms in the abdominal area and they die quickly. Dry FIP causes brain damage and balance issues, blindness, aggression and may take slightly longer and is more difficult to treat. The latter may also cause intestinal lesions.

Chelsea was due for a check-up on Tuesday, the 11th of October, but the ongoing fever and fatigue worried me enough that I took her in a day earlier. She was hospitalised again, and the labs chased up for results, which we received on Friday, the 14th of October, the day after she’d been discharged: it was indeed FIP and not small cell lymphoma. The initial diagnosis was wet FIP because of the intestinal growth, even though they never managed to get any fluid from her stomach.

We then had to take very quick action and start treatment immediately. Because the tablet options are imported and take time to bring in, we had to start with injections. I’ve been quite clear that I wouldn’t want to subject her (and me) daily for at least 84 consecutive days to the most painful injection known, but I had to give her immediate support to start fighting the disease. She handled the first injection really well – and without a sedative two hours before, as we’d start with from the next day.

We ordered tablets and continued taking her daily for the injections – in the end for the first 12 days until the tablets arrived. Friends and strangers started supporting and rallying around us with advice, prayers and good wishes. The daily sedative and drive to the vet took a bit of a toll (on me), but she started responding a bit. The trick is also to not interrupt treatment, as one effectively has to restart again at Day 1; treatment is between 80 and 90 consecutive days, with 84 a good average.

Another fact about the injections, is that they’re locally available and considerably cheaper than the imported tablets – but we had to make a plan. There are also two ways of treating: Remdesivir injection, and then the body manufactures GS-441524, or GS-441524 directly as mixed locally by a compounding veterinary pharmacy or the GS-441524 imported tablets. Chelsea was initially on the GS-441524 injections, and when we swopped to Remdesivir injections, she struggled to absorb the volume of thick, acidic liquid from one day till the next day when we were already lining up for the next injection. She also didn’t feel great afterwards and was often hiding in a safe place all night.

On Day 13 of treatment, we swopped to tablets. She started on 2.5 daily as per her body weight for wet FIP and it was a huge improvement to her, not having injections and not travelling. By this time, we’d swopped to Fourways Veterinary Hospital and Specialist Referral Centre and under the capable care of Dr Estee van Zyl. On her next check-up on Monday, the 31st of October, she was all well, had gained a bit of weight and we could go to three tablets daily to cater for the weight gain. Dr Estee advised placing them in a clear capsule, which really helped with administering.

Unfortunately, Wednesday, the 2nd of November saw her nauseous and vomiting. We were advised to bring her in. Her fever was spiking again and it was recommended we leave her there, also to administer Remdesivir via drip as that can be quite beneficial in the treatment process. At about 20h00 we received a call from the doctor on duty that she’d had a setback and was comatose, by which time they removed the drip. She regained consciousness and they were monitoring her closely. She came home after two days, had three more injections, after which we continued the tablet treatment on receiving confirmation on the efficacy.

I avoided Googling and reading up about the disease at all costs – instead I consulted with Dr Estee and spoke with the mentor (Penny Steyn) of a friend (Gillian Lentin) who’d taken over a cattery and had had her brush with FIP then. I’d been a bit concerned initially about the diagnosis and was hoping to consult with a specialist at JSV about it (Dr Rowena was away at the time for three weeks at Onderstepoort), so early November saw me reading an article by Dr Pedersen about the treatment and progress and differences between wet and dry cases. It stated that if the wrong diagnosis is made and they appear to progress well and then just have a slight change in condition, it may just be dry FIP and not wet FIP.

Our constant struggle with a slight fever, her initial improvement and then a just-visible deterioration, coupled with the loss of consciousness on the drip and the fact that we could never draw any light yellow, sticky liquid from the abdomen, made me discuss my concerns with Dr Estee. She was advised of the initial diagnosis by the lab and JSV, and on Monday, the 14th of November (Day 32 of treatment) immediately increased her dosage to four tablets per day to cater for the neurological version. I ordered more tablets based on this scenario, plus a number of extra tablets to cater for weight gain and/or additional days after the envisaged 84 days.

What made me also think about the neurological version is the fact that only one other cat treated by Dr Estee had a similar fainting episode on the drip – I wondered if this was indicative of the fact that the centre of the dry FIP is in the brain and therefore that a large dosage of Remdesivir intravenously would naturally cause the reaction to be neurological? The point about the treatment is that it’s very recent and that long-term data isn’t available as yet. Also, a lot of work is still ongoing and one accepts that with the diagnosis of this dreaded disease comes the uncertainty: there is hope, and lots of it, but no clear and firm answers to everything. And not all cats react exactly in the same manner.

Once we increased the dosage, however, we turned a corner. From then on, the only times when Chelsea did have a slight fever was when her weight gain necessitated a dosage rise. Our next check-up was scheduled for the 2nd of December. A few blood results weren’t in the ballpark and her weight was stable with no fever, so we continued on four tablets daily. We also got a prescription for nausea and vomiting, which we only needed to give her once on the 18th of December and never again.

Our 84-days goal date was in the first week of January, which prompted us to see Dr Estee on Tuesday, the 20th of December, before the Christmas break, to make sure we had everything under control, plus a plan for the holiday period, should anything happen.

Chelsea did have a slight fever again but had gained some more weight, and some bloods weren’t in normal range, so we increased the tablet daily dose to five. We were now on day 68 of FIP treatment.

Chelsea continued to humour me with the daily pill procedure and swallowed it dutifully – often during the last month accompanied by just a growl. She’s quite a fierce little redhead and has a temper to match. But she didn’t scratch or bite me once.

On Wednesday, the 5th of January, we reached day 84, amazed at how quickly it seemed to have flashed past. She had a slight fever again, but most bloods looked good and she’d gained another 300 grams. Our thin little girl had developed a bit of a tummy – fat even! We repeated the serum amyloid A test again; while we waited on that result, we increased her tablet dosage to six per day. We also ordered additional tablets for a week (at the same dosage she stopped at, in case of a relapse, to enable us to start treatment immediately while looking at options/find treatment).

The serum amyloid A results came back on Tuesday, the 10th of January (Day 89): from 11.1 earlier, they were now at 2.2. The lower this result, the better, and it’s used to check the efficacy of treatment, Dr Estee explained to me. It’s not a standard test and gets done by Onderstepoort Veterinary Academic Hospital (OVAH), but we’d had it done upfront as a benchmark, and once in the middle, to help us decide when to stop treatment.

We could stop treatment!

We had enough tablets left to continue until Friday, the 13th of January, which was officially day 92 of FIP treatment – and the day we stopped.

This in itself was quite a stressful moment – the treatment almost became a crutch to lean on and provide certainty – while ongoing. Having to face the possibility of a relapse during the monitoring phase was our next obstacle. Treatment entails a minimum of 84 days of tablets/injections, plus the same length of time monitoring, with vet visits and formal tests every four weeks to monitor progress. We’re also aware now that the neurological version is the one most likely to relapse, but no studies have yet been done on relapse rates.

No formal studies have been conducted to demonstrate the relapse rate of treatment with GS-441524, but relapses are estimated to be between 5 and 15%, with most relapses being associated with neurological disease (Jones et al., 2021; Pederson, n.d.). Unfortunately, there’s no way to predict which cats will relapse. A recent study that has investigated the use of alpha-1-acid-glycoprotein in predicting which cats will relapse (Addie et al., 2022) has shown promise, but this assay is unavailable in South Africa. Deciding if it is safe to stop treatment should be based on clinical progress, with weight
gain being a crucial prognosticator and normalising haematological and biochemical parameters (Pederson, n.d.).”

The above is quoted from the article Dr Rowena Watson wrote for the August 2022 edition of the South African Veterinary Association VetNews magazine.

Armed with this, although nervous, we celebrated the end of treatment day with her and started surrounding her with positive, happy messages. While trying to not stress about the relapse and putting any stress or strain on her, but watching her like a hawk.

Dr Estee requested us to take her temperature reading two days before the first scheduled visit, to rule out the vet visit slight increase as a possibility with her. I decided to do a weekly reading for our own peace of mind. First week was 38°C, the second week 37.2°C, and the week before the visit 38.2°C. On the 2nd of February, at the vet visit her temperature was indeed up at 39.2°C, but all bloods looked really good, she’d gained another 300 grams, and a very thorough abdominal sonar revealed nothing out of the ordinary at all.

We’re on Day 31 post treatment today and are delighted that our little girl is eating, playing and interacting with the world like any normal little kitten her age. Although not required to diet, she also doesn’t have to gain any weight necessarily. We’re slowly relaxing about the post-treatment possible relapse, also because we do know now of Dr Rowena and Dr Estee in Johannesburg having treated other cats successfully.

We’re also aware that the global research into FIP is ongoing, including on felines that have relapsed, and that there’d be options available for Chelsea, should it happen. A big deterrent is the cost of the (imported) tablet treatment and the prohibitive nature of the painful (for both patients and their humans) but more affordable and locally available injection route. Dr Estee reminded me more than once how difficult FIP is as a disease to treat and that no question or concern from us would ever be treated lightly – it helped us immensely through this uncharted territory.

Dr Rowena has been in touch with the local compounding pharmacy on an ongoing basis to investigate the availability of a local tablet – she’ll be able to confirm any progress on this front. We sincerely hope this will become an option. (Editor: It is indeed available now.)

The other issue is that all veterinarians until 2020 were trained that there’s no cure for the disease, so your local vet may not have been informed of the latest research and the ongoing work globally on the progress with FIP. Do feel free to mention Dr Rowena and Dr Estee and the work they’re doing to your vet or call them for advice. Both are at specialist veterinary centres in Johannesburg and are doing amazing work, Dr Rowena being the trailblazer with her first and very own kitty.

So far in this process, we’re so delighted that we’ve managed to get our little Chelsea girl back to health. We’re eternally grateful to Dr Tanya at Linden Vet to have picked up the issue and referred us; Dr Fanie at JSV for the careful surgical work; and Dr Rowena (JSV) and Dr Estee (FSVH) for helping and guiding us on an ongoing basis.

Chelsea trusted us with her little life to care for her when she got out of her basket so confidently – we’re so grateful for these good people who’ve helped us deliver that!

We’ll regularly supply updates on her progress henceforth to be posted to https://www.facebook.com/happytailsmagazine.co.za/.

#FIP #felinecoronavirus #felineinfectiousperitonitis #onderstepoort #treatingFIP #FIPSouthAfrica

Monday 13 February 2023

Update in September 2023: This ordeal happened exactly one year ago. On the final day of observation in April when we got the all-clear from Dr Estee, Chelsea came and sat with me and took my hand in both her paws and licked every finger softly, with soft bites in between. All the time looking me intently in the eyes. It was a really special moment; she knew that she was at death’s door and that we pulled her through.

The fact that she allowed me on my own every day to administer tablets without even a scratch, says it all. We can barely give her deworming medicine now!

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