Feline infectious peritonitis

Feline infectious peritonitis (FIP) is a common and aberrant immune response in cats to infection with feline coronavirus (FCoV).

The virus and pathogenesis of FIP

Feline infectious peritonitis is a viral and fatal immune disease caused by the mutated FCoV. FCoV is a common virus found in most cats, however only few (less than 10%) develop FIP from mutation of the coronavirus. When a cat develops FIP, they can develop either a wet or dry form of the virus, both resulting in eventual mortality.

FCoV is a virus of the gastrointestinal tract. Most infections are either asymptomatic or cause diarrhea, especially in kittens, as maternally derived antibody wanes at between 5 and 7 weeks of age. The virus is a mutation of feline enteric coronavirus (FECV). From the gut, the virus very briefly undergoes a systemic phase, before returning to the gut where it is shed in the feces.

The pathogenesis of FIP is complex. There is a general consensus that FIPVs arise from mutations enabling them to enter or replicate more successfully in monocytes (a type of white blood cell). Many aspects of virus–host interactions affecting the disease remain uncertain, however, such as the factors that influence disease form (wet or dry), outcome (death or resistance), and host susceptibility.

Scientist have yet to explain why only few cats will develop the disease, while there has been research on if the disease has a genetic linkage that increases a cat's risk of developing FIP from FCoV. The virus, FCoV, is transmissible from cat to cat.

Although the virus is spread via FCoV, only a small precent of cats will develop FIP . It is more common in cats under two years of age, with a small number of geriatric cats also developing the disease.

A study on 59 FIP infected cats found that, unlike FCoV, feces from FIP infected cats were not infectious to laboratory cats via oronasal route. FCoV is common in places where large groups of cats are housed together indoors (such as breeding catteries, animal shelters, etc.). The virus is shed in feces, and cats become infected by ingesting or inhaling the virus, usually by sharing cat litter trays, or by the use of contaminated litter scoops or brushes transmitting infected microscopic cat litter particles to uninfected kittens and cats. FCoV can also be transmitted through different bodily fluids. The virus is easily spread through direct contact between cats. The most common form of spreading is through saliva, as most multiple cat homes share food and water dishes. Another major form of spreading is grooming or fighting. When an infected cat grooms a healthy cat, it leaves its contaminated saliva on the fur. Later, when the healthy cat goes to groom themself, it ingests the contaminated saliva and then becomes infected.

Two of FIP have been identified and examined based on how they cause the virus to mutate. Factors also examined have been host genetics, environmental causes, and breed.

Clinical signs

thumb|FIP effusive fluid

There are two main forms of FIP: effusive (wet) and non-effusive (dry). While both types are fatal, the effusive form is more common (60–70% of all cases) and progresses more rapidly than the non-effusive form.

However, symptoms have been noted to occur before these stages including When fluid accumulates in the chest, cats experience difficulty breathing as more pressure is applied around the lungs. Fluid can also fill in the abdomen, resulting in a distended or swollen belly.

Non-effusive (dry) FIP

Dry FIP will also present with lack of appetite, fever, jaundice, diarrhea, and weight loss, but there will not be an accumulation of fluid. Typically a cat with dry FIP will show ocular or neurological signs. For example, the cat may develop difficulty in standing up or walking, becoming functionally paralyzed over time. Loss of vision is another possible outcome of the disease. Instead, inflammation occurs in the dry form and can include multiple organs and areas of the body such as: the brain, liver, eyes, and intestines. Treatment of these symptoms may vary and are more focused on treating the disease overall as once the disease progresses, it is almost always fatal. Nonetheless, that does require that a sample be sent to an external veterinary laboratory. Within the veterinary hospital there are a number of tests that can rule out a diagnosis of effusive FIP within minutes:

Measure the total protein in the effusion: if it is less than 35 g/L, FIP is extremely unlikely.
Measure the albumin to globulin ratio in the effusion: if it is over 0.8, FIP is ruled out; if it is less than 0.4, FIP is a possible—but not certain—diagnosis.
Examine the cells in the effusion: if they are predominantly lymphocytes (a type of white blood cell), then FIP is excluded as a diagnosis.

Diagnosing non-effusive FIP

Non-effusive FIP is more difficult to diagnose than effusive FIP because the clinical signs tend to be more vague and varied: the list of differential diagnoses is therefore much longer. Non-effusive FIP diagnosis should be considered when the following criteria are met:

History: the cat had an opportunity to become infected with FCoV, such as originating in a breeding or rescue cattery, or the recent introduction of a purebred kitten or cat into the household.
Clinical signs: the cat has become anorexic or is eating less than usual; has lost weight or failed to gain weight; has a fever of unknown origin; intra-ocular signs; jaundice.
Biochemistry: hypergammaglobulinaemia; raised bilirubin without liver enzymes being raised.
Hematology: lymphopenia; non-regenerative—usually mild—anaemia.
Serology: the cat has a high antibody titre to FCoV: this parameter should be used with caution, because of the high prevalence of FCoV in breeding and rescue catteries.

Non-effusive FIP can be ruled out as a diagnosis if the cat is seronegative, provided the antibody test has excellent sensitivity. In a study that compared various commercially available in-house FCoV antibody tests, the FCoV Immunocomb (Biogal) was 100% sensitive; the Speed F-Corona rapid immunochromatographic (RIM) test (Virbac) was 92.4% sensitive and the FASTest feline infectious peritonitis (MegaCor Diagnostik) RIM test was 84.6% sensitive.

Veterinarians also refer to differential diagnoses when it comes to diagnosing FIP itself. These diagnoses include:

Septic Peritonitis
FIV or FeLV
Congestive Heart Failure
Pancreatitis
Mycobacteriosis

Diagnosing FIP with the tools available leads accurate results which are essential when it comes to treating and remission of FIP.

In naturally infected cats, a recovery rate of over 80% has been observed with GS-441524 treatment in several studies and in treatment programs in countries where the drug is legalised.

In several countries oral GS-441524 tablets (and its injectable prodrug remdesivir) became legally available to vets for the treatment of FIP in cats, for example in Australia, the Netherlands,, the United Kingdom (since August 2021),

GC376

An experimental antiviral drug called GC376 was used in a field trial of 20 cats: seven cats went into remission, and 13 cats responded initially but relapsed and were euthanized. This drug is not yet (as of 2017) commercially available.

Molnupiravir

Facing a high-fatality FCoV-23 outbreak on the island nation of Cyprus, on 8 August 2023 the government released 80,000 anti-COVID molnupiravir pills from its national COVID-19 stockpile, in a bid to solve the feline coronavirus crisis in a more cost-effective manner.

Immunostimulants

Immunostimulants are drugs that make the immune system more active against the virus. The most common drugs of this class for treating FIP are either recombinant feline interferon omega (Virbagen Omega, Virbac) or human

interferon alfa-2b. Since the human version ends up being targeted by the immune system for being a foreign antigen, the feline version feline interferon is more effective.

An experimental polyprenyl immunostimulant (PI) is manufactured by Sass and Sass and tested by Dr. Al Legendre, who described survival over 1 year in three cats diagnosed with FIP and treated with the medicine. In a subsequent field study of 60 cats with non-effusive FIP treated with PI, 52 cats (87%) died before 200 days, but eight cats survived over 200 days from the start of PI treatment for and four of those survived beyond 300 days.

Anti-inflammatory drugs

It is recommended to use an anti-inflammatory drug against FIP.

Prevention

Stopping the spread of FIP can be difficult, especially with only one known FDA approved treatment available in the United States. Because of this, it is important to be proactive and try to prevent FIP before the disease can begin its destructive turmoil. Preventing FIP also differs depending on the facility or environment of the cat.

In shelters and areas with high numbers of cats in confinement, prevention is essential as it only takes one cat to start a chain-reaction and spread of FIP. Prevention includes: antibody testing, environmental enrichment to decrease stress, multiple litter boxes that are cleaned regularly to prevent the spread in fecal matter.

Disinfection is also a key factor in stopping the spread of FIP. FCoV particles can be disinfected with products such as diluted bleach, UV light, and heat.

Vaccination

There is no effective vaccine against FIPV. DNA vaccination with plasmids encoding FIPV proteins failed to produce immunity. Rather, it was observed that antibodies to the FIPV spike protein exacerbate the disease.

In film

A 2018 film titled Aeris, by Paul Castro Jr. and Aly Miller, and starring Frank Deal, Arabella Oz and Betsy Aidem, is about a kitten born with FIP that is purchased from a pet store and the owners' twelve days with it. The film received an award at the 2018 Garden State Film Festival in the Narrative Short category and was a Gold Kahuna winner at the 2018 Honolulu Film Awards.

Explanatory notes

References

External links

FIP Informational Brochure from the Cornell Feline Health Center
UC Davis Center for Companion Animal Health
FIP (Felipedia.org)