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FIP – Feline Infectious Peritonitis – May No Longer Be A Death Sentence For Cats

There may now be viable treatment for cats with FIP.

Long considered an imminently fatal infectious disease in cats, feline infectious peritonitis, aka., FIP, may now be treatable in some cats infected with the disease. This comes, unfortunately, with one giant caveat: the antiviral agents that seem to have some efficacy in treating the disease, GS-441524 and GC376, are not FDA approved, still held up in clinical trials.

In desperation fueled by a combination of hope that treatment exists and despair that cat owners’ FIP infected cats cannot get it, cat owners are turning to black market sources to obtain the drugs to treat their beloved feline family members. Within the past four years, antiviral agents GS-441524 (patented by Gilead Sciences) and GC376 (patented by Kansas State University) have been shown to reverse the progression of FIP in clinical trials involving several dozen infected cats. The agents interfere with the virus’s ability to hijack the body’s immune system. While they are not available on the open pharmaceutical market, in China, where cat ownership is becoming increasingly popular and cases of FIP are on the rise, entrepreneurs have begun producing versions of these antivirals and some are making their way to cat owners around the world, including the US.

FIP was first identified as a clinical infectious disease in the 1950s. It has since become one of the most the most researched infectious disease of cats. FIP is triggered by mutations that occur in a common and generally mild feline coronavirus that infects the small intestine. These mutations allow feline coronavirus to escape epithelial cells in the lower intestine and infect a primary immune system cell, a type of white blood cell called the macrophage. This new macrophage-infecting virus is known as FIP virus.

About 10% of cats exposed to this mutant variant go on to develop FIP after a subclinical period ranging from a few days to a year or longer. FIP is imminently fatal in all cases if left to run its normal course. FIP is regarded as the leading cause of death among young cats from foster/rescues, shelters, and catteries.

There are two forms of FIP, known as the wet and dry forms. In wet form FIP, in my experience the more common form, fluid resulting from inflammation accumulates in body cavities, most commonly in the abdomen or around the lungs. In dry FIP form, the cat develops tumor-like lesions on organs of the abdomen, lungs, eyes and/or brain. Early clinical signs of FIP include fever, loss of appetite, weight loss and depression. Case progression will depend on which form, and which organs are primarily affected and include: distended/fluid fill abdomen, incoordination, seizure, clouding of the the eyes, and labored breathing.

FIP can be difficult to diagnose, especially in dry form, which can present similarly to toxoplasmosis, certain fungal infections, or lymphoma. A positive FIP test does not necessarily distinguish between a cat that has been exposed to a general feline coronavirus or the deadly FIP variant. However, a negative test would definitively rule it out, but this is rare since it is generally accepted that 80% or more cats have been exposed to feline coronavirus. Given this lack of definitive ability to distinguish between feline coronavirus and FIP, final diagnosis is often based on history, presenting clinical signs, and other supportive lab data.

Many cats with FIP are euthanized. Others are given symptomatic treatment with the faint hope that the immune system ultimately win out over the virus (in 19 years of practice, I have never seen this happen. When I first graduated veterinary school in 2002, the immune messenger molecule, interferon, was being tried, as it had previously shown the ability to boost the body’s immune system against certain viruses. It would ultimately show little benefit for FIP cats.

The names GS and GC that precede each FIP drug are derrived from small molecules that easily pass from the bloodstream into infected cells. Once inside infected cells, they target specific viral proteins that control viral replication. GS inhibits the formation of viral RNA early on and GC inhibits the formation of mature viral proteins at a later stage. In trials so far, GS has been shown to be the more effective.

Although no GC or GS FIP drugs have been approved for use in China, the companies that make these drugs are apparently under no meaningful legal restraints in manufacturing them and selling them. “Brands” that have been identified as legitimate drugs that deliver on the content and efficacy of the drugs have been identified by FIP social media groups: Mutian II, Mark’s, Andy’s and Shire to name a few. Treatments are purchased through intermediaries on the internet, often for thousands of dollars.

The potential problems with this are clearly glaring. With no official governing body overseeing the collection of money, one may just be putting money out into cyberspace never to be seen again. If one is lucky and product actually does arrive, with no government oversight proving quality control and integrity of ingredients, processing etc., one may not know what one is administering to one’s cat.

Still, many view these circumstances and unknowns as having nothing to lose with an otherwise terminally ill patient. I have three veterinary colleagues have not only gone along with their client purchases of these agents for their FIP infected cats, but aided them in the administration. All three colleagues have reported a 100% success rate thus far.

Where this leaves the veterinary practitioner is a very gray area. Being complicit in the administration of an unapproved drug to a patient is a potentially serious offense that risks one’s veterinary and DEA licenses, thus potentially risking one’s ability to practice medicine and prescribe medication, respectively.

I have only recently learned of these new treatments for FIP and have yet to be presented with a case of FIP to have this discussion with clients. My stance for now will be to inform clients of the existence of these drugs and leave it to them to decide if they are prepared to personally take the risks of lost money, bogus product, and understand that I cannot in any way legally assist in the administration of the drug.

My hope is that the current US GS and GC patents will make it out of FDA clinical trials and get approval status in the near future. After a whole career of advising owners of their cats’ FIP diagnosis and grave prognosis, it is exciting to know that any day now, there may be approved and effective treatment available for this horrible disease.

Dr. Roger Welton is a practicing veterinarian and highly regarded media personality through a number of topics and platforms. He is the author of The Man In The White Coat: A Veterinarian’s Tail Of Love. In addition to being passionate about integrative veterinary medicine for which he is a globally recognized expert, Dr. Welton was also an accomplished college lacrosse player and remains to this day very involved in the sport.  He is president of Maybeck Animal Hospital , general partner of Grant Animal Clinic, and runs the successful veterinary/animal health  blogs Web-DVM and Dr. Roger’s Holistic Veterinary Care.  Dr. Welton fulfills his passion for lacrosse through his lacrosse and sport blog, The Creator’s Game.