Feline Infectious Peritonitis

Laurie Anne Walden, DVM

Feline infectious peritonitis (FIP) is a serious disease caused by a coronavirus infection in cats. The disease is usually fatal, although a new antiviral drug under investigation has had promising results in some cats.
 
Cause
Cats very commonly carry a strain of feline coronavirus that lives in cells of the intestines. This virus, feline enteric coronavirus, does not cause disease in most cats. In some cats, though, the virus mutates into a disease-causing strain that invades a type of white blood cell and spreads through the body. This strain is FIP virus (FIPV). The disease it causes, FIP, results from the body’s immune response to the infection.
 
Transmission
Feline enteric coronavirus spreads easily among cats housed together, especially in shelters and catteries. This virus is shed in the feces, and cats can be infected if they share litter boxes or have close contact with infected cats. Cats with no symptoms can spread the virus to other cats. Cats are often exposed to feline enteric coronavirus as young kittens.
 
Why feline enteric coronavirus mutates into FIPV in some cats is not fully known. Virus genetics and individual cat factors (genetics, immune function, and possibly environment) are likely to be involved. Most cats that develop FIP are kittens or young adults. Cats housed in groups, male cats, purebred cats, and cats that have not been spayed or neutered are at higher risk than others for FIP.[1,2]
 
The mutated virus strain, FIPV, does not appear to spread directly from cat to cat. Feline enteric coronavirus and FIPV are not known to infect humans.
 
Symptoms
Most cats exposed to feline enteric coronavirus do not become ill. Some cats have an episode of diarrhea or vomiting, which is usually mild.
 
Because FIPV spreads throughout the body, FIP affects many body systems and can cause a wide range of symptoms. The clinical signs are not specific; they can be caused by diseases other than FIP.
 
Typical FIP signs are caused by fluid accumulation in the abdomen and chest, by inflammatory changes in various parts of the body (such as kidneys, nervous system, liver, heart, or eyes), or both. The symptoms depend on the body system affected and can change over time in the same cat. These are some of the possible symptoms of FIP:

• Loss of appetite
• Weight loss
• Fever
• Decreased energy
• Swollen belly
• Labored or open-mouth breathing
• Stumbling or loss of balance
• Tremors or seizures

 
Diagnosis
Diagnosing FIP is not straightforward and can’t currently be done with a simple blood test. Because so many cats have been exposed to feline enteric coronavirus, a positive antibody test (indicating virus exposure) doesn’t mean that a sick cat has FIP. The diagnosis is usually based on a combination of clinical signs, results of baseline blood and urine tests, and analysis of abdominal fluid and samples taken from affected organs.
 
Treatment
Until recently, the prognosis for cats with FIP was uniformly bleak. Conventional treatments, including various antiviral medications and drugs to manage the immune response, have had variable success at prolonging cats’ survival times. Cats are usually treated with supportive measures to maximize their comfort for as long as possible.
 
A new antiviral drug, GS-441524, successfully treated some cats with FIP in a study published in 2019.[3] This drug is closely related to remdesivir, which was originally developed as a treatment for Ebola virus infection and is now being studied as a potential treatment for coronavirus disease 2019. GS-441524 may prove to be effective for some cases of FIP, but it is not currently approved by the US Food and Drug Administration.
 
Prevention
Preventing FIP is difficult because feline enteric coronavirus spreads so easily among cats and because the factors that cause it to mutate to FIPV aren’t known. A vaccine for FIP has been marketed, but it is not very effective and is not currently recommended for use in cats.[4] Practicing good husbandry in high-density environments like shelters and keeping individual cats in good health might reduce the risk.
 
References
1. Levy JK, Hutsell S. Overview of feline infectious peritonitis. Merck Veterinary Manual. Updated January 2014. Accessed May 6, 2020. https://www.merckvetmanual.com/generalized-conditions/feline-infectious-peritonitis/overview-of-feline-infectious-peritonitis
2. Felten S, Hartmann K. Diagnosis of feline infectious peritonitis: a review of the current literature. Viruses. 2019;11(11):1068. doi:10.3390/v11111068
3. Pedersen NC, Perron M, Bannasch M, et al. Efficacy and safety of the nucleoside analog GS-441524 for treatment of cats with naturally occurring feline infectious peritonitis. J Feline Med Surg. 2019;21(4):271‐281. doi:10.1177/1098612X19825701
4. Scherk MA, Ford RB, Gaskell RM, et al. 2013 AAFP Feline Vaccination Advisory Panel Report. J Feline Med Surg. 2013;15(9):785‐808. Published corrections appear in J Feline Med Surg. 2013;15(11):NP2 and J Feline Med Surg. 2014;16(1):66. doi:10.1177/1098612X13500429
 
Photo by Timothy Warrington

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