What is pif in cats?

According to the Morris Animal Foundation, FIP is a leading cause of death in kittens and young cats and is most common in indoor, multicat environments such as shelters and catteries. In October 2015, Morris made a three-year, $1.2 million commitment to fund research that will advance understanding of feline infectious peritonitis and to dedicate resources to stop the disease.

Winn Feline Foundation has funded FIP research through the years, including 21 projects through the Bria Fund for FIP research. Winn devoted its 2017 symposium, June 29 in Chicago, to FIP prevention and treatment. The speaker was longtime FIP researcher Dr. Niels C. Pedersen, professor emeritus at the University of California-Davis School of Veterinary Medicine.

The American Association of Feline Practitioners focused its 2017 conference, Oct. 19-22 in Denver, on feline infectious diseases and pediatrics, starting with FIP. Dr. Pedersen spoke on "Risk Factors Affecting the Incidence of FIP in Dense Multi-Cat Environments" and "Use of Novel Anti-viral Drugs to Treat Cats with Naturally Occurring FIP."

Some of the questions after the first session illustrated the difficulties in preventing and treating the disease. Audience members asked about controlling FIP in a kitten rescue, managing a pair of young cats in a home, and interpreting diagnostic test results. None of the answers was clear-cut.

Dr. Pedersen presented hope in the second session. He has participated in trials on two antiviral drugs that have led to remission in some cats with FIP.

"Antiviral drugs are the answer," he said. "We've opened the door and shown that we can successfully cure a large percentage of these cats."

Dr. Pedersen started studying the disease in 1964. Back then, FIP went hand in hand with feline leukemia. The incidence of both conditions dropped after release of a vaccine against feline leukemia virus, but now the incidence of FIP is rising."A lot of veterinarians claim they don't see this disease, but I think we're now starting to recognize all of the forms that occur—and especially some of the chronic dry cases," Dr. Pedersen said. "As we start to recognize the full spectrum of the disease, we'll start seeing more of it."

(Cat photos provided to Dr. Niels C. Pedersen by the cats' owners)

The basic virus is feline enteric coronavirus, an RNA virus that is ubiquitous throughout the world and spread via the fecal-oral route. Up to 60 percent of cats in multicat environments shed the virus at any given time. There are two serotypes, with type 1 being predominant and type 2 accounting for 5 to 20 percent of cases.

Both types can mutate during primary or secondary infection, transitioning to attack macrophages. One study found that mutation occurs in about 20 percent of infections, but the incidence of FIP is 0.3 to 1.3 percent among all cats in studies done in North America and Europe.

"The disease is relatively uncommon compared to the rate of the mutations occurring," Dr. Pedersen said. "Most cats that undergo this mutation in their body have the ability to immunologically respond to it." The question is why some cats fail to mount an effective immune response.

The incidence of FIP in a cat population can be as high as 10 percent or as low as zero—and can fluctuate. At high risk is any dense cat population with kittens as part of the equation. High-risk populations include cats at foster and rescue organizations and dense populations of free-roaming cats.

Risk factors for FIP have to do with the host, environment, and agent. The host factors include early weaning, age at the time of coronavirus infection, genetic susceptibility, stresses at the time of enteric coronavirus exposure, and the occurrence of FIP-causing mutants. Stresses at the time of coronavirus exposure can include weaning, overcrowding, elective surgical procedures, vaccinations, and concurrent infections.

Environmental factors include overcrowding, mixed ages, shared litter boxes, and diet. Among the agent factors are the severity of the coronavirus exposure, the strain of coronavirus in terms of virulence and mutability, and possibly the serotype of coronavirus.

"Cats do not transmit FIP virus to each other," Dr. Pedersen said. The macrophage pathogen is present only in diseased tissues and no longer replicates in the gut. The virus that is passed from cat to cat is the ubiquitous and largely nonpathogenic parent enteric coronavirus.

In the announcement about its FIP funding, the Morris Animal Foundation characterized the disease as difficult to diagnose. Nonspecific, early signs of illness include loss of appetite, weight loss, signs of depression, rough hair coat, and fever. Later signs can include fluid accumulation in the abdomen.

Dr. Pedersen believes FIP is not hard to diagnose. He said, "FIP is a death sentence, and death sentences require definitive proof, don't they?" Not so, he said. Veterinarians know what it is when a young cat comes in with fever, a big belly full of fluid, and other signs. Dr. Pedersen said the diagnosis can be made with a high degree of certainty on the basis of signalment, clinical signs, physical findings, and a simple fluid analysis—including cell count and protein concentration.

Supportive care will prolong life, and some cats with FIP can live in a state of chronic disease for weeks, months, or, rarely, a year or more. He said, "Immunostimulants and immunosuppressives have no curative powers. Vaccines are not effective. That leaves us with antiviral agents."

Dr. Pedersen said veterinarians must learn from research on human RNA viruses such as HIV, hepatitis C virus, influenza virus, and Ebola virus. It is possible to make drugs that interfere with specific replication processes of viruses.

"The results of our preliminary field studies with two drugs, a protease inhibitor and a nucleoside inhibitor, are showing great promise in curing certain forms of FIP," Dr. Pedersen summarized after the AAFP conference.

One candidate for treating FIP is the protease inhibitor GC376. Researchers at Kansas State University; Wichita State University in Wichita, Kansas; and UC-Davis studied the drug in eight cats with experimentally induced disease. The results appeared in "Reversal of the progression of fatal coronavirus infection in cats by a broad-spectrum coronavirus protease inhibitor" on March 30, 2016 in PLoS Pathogens, an online journal of the Public Library of Science. The study is available at http://jav.ma/FIPtreatment.

According to the abstract, "We found that antiviral treatment led to full recovery of cats when treatment was started at a stage of disease that would be otherwise fatal if left untreated."

Researchers at the universities conducting that study plus Washington State University then conducted a field trial of the drug in 20 cats with naturally occurring disease. The results appeared in "Efficacy of a 3C-like protease inhibitor in treating various forms of acquired feline infectious peritonitis" online Sept. 13 ahead of print in the Journal of Feline Medicine and Surgery. The study is available at http://jav.ma/FIPtreatment2.

According to the abstract, "GC376 showed promise in treating cats with certain presentations of FIP and has opened the door to targeted antiviral drug therapy."

At the AAFP conference, Dr. Pedersen explained that all the cats returned to normal health, but 14 cats had fatal relapses not responsive to the drug. Six cats went into remission, with one receiving the nucleoside inhibitor EV0984. The major adverse effect was inhibition of the formation of permanent teeth in young kittens.

Dr. Pedersen also described unpublished research on EV0984, which inhibits nucleoside reverse transcription. Researchers studied the drug against experimental FIP, then went into a field trial with 30 cats. Four cats died within one to two weeks of related and unrelated complications, but 26 cats achieved complete remission of disease signs. Two-thirds of the latter cats are in long-term and hopefully permanent remission after 12 weeks or so of treatment.

One-third of cats had disease relapses after stopping treatment; one failed to respond to re-treatment, while the rest have responded well to re-treatment. The latter cats may require prolonged or indefinite therapy. There were no major adverse effects. At the conference, Dr. Pedersen cautioned that commercialization of drugs is not easy. Afterward, he continued, "We feel that FIP-specific antiviral drugs will become the treatment of choice for FIP, but we are reluctant to make guesses on when they might appear in the hands of veterinarians."

In the book "50 Years of Advancing Feline Medicine" celebrating Winn's upcoming anniversary in 2018, Dr. Pedersen concluded, "The quest for a cure has been slow, but scientists around the world have built a solid base of knowledge of FIP that is finally yielding exciting breakthroughs, especially in the area of anti-viral drug therapy."

Source: Dr. Niels Pedersen, 2017 American Association of Feline Practitioners Conference

FIP was previously fatal for most cats. However, in the last 3 years, significant developments have occurred in treatment. Studies have shown that antivirals can be effective in curing FIP. This has led to a growth in illegal supplies of these medications, sold to understandably worried caregivers. Since 2021 a legal supply of remdesivir and GS-441524 has been available in the UK and Australia, and via export to other countries. Please click here for more specific information about these drugs and speak to your vet to discuss treatment options if your cat is diagnosed with FIP.

FIP is caused by infection with a virus known as feline coronavirus. Coronaviruses are a common group of viruses that often infect the upper respiratory tract (nose and throat) or gastrointestinal tract (intestines) in different animals. COVID-19 is a coronavirus but the coronavirus causing FIP is not the same and only infects cats. Coronavirus infection is extremely widespread in cats, especially where large numbers of cats are kept together. It is estimated that 25–40% of household pet cats have been infected with FCoV, but the infection rate increases to 80 – 100 per cent for cats kept in multi-cat households or colonies.

Coronaviruses are common and found in the faeces of many cats. In most cats, infection causes no signs or just mild diarrhoea that resolves without treatment. However, occasionally, the virus mutates (changes) inside a cat, and if their immune system reacts in a certain way, they could develop a disease called FIP. This is important, as finding coronavirus in a cat does not mean they have FIP, and it is not possible to consistently tell the difference between a coronavirus causing FIP and one causing no signs at all by just finding the virus itself.

In a cat that develops FIP, the virus spreads throughout the body and can cause a wide range of different signs due to the way it interacts with the cat’s immune system.

FIP can cause many different clinical signs, depending on the parts of the body affected and how the immune system reacts. Early signs of FIP are usually very vague with a fluctuating fever (high temperature), lethargy and reduced appetite being common. After a period of several days or weeks (or sometimes even many months) other signs usually develop. Classically, FIP has been divided into ‘wet (effusive)’ and ‘dry’ forms, but actually cats are likely to have both at different times, or a mixture of both presentations. One of the challenges of diagnosing FIP is that the clinical signs are often vague and not specific for FIP and can be seen with other diseases.

In this form or stage of disease there is accumulation of fluid within the abdominal cavity (resulting in abdominal distension) and/or the chest cavity (resulting in breathing difficulties). The fluid accumulates because infection with FIPV causes damage to and inflammation of blood vessels (called ‘vasculitis’) which results in fluid leaking from the blood into the abdomen or chest. Cases that develop fluid accumulation in the abdomen are responsible for the original name of this disease, ‘peritonitis’ referring to the inflammation that occurs in the lining of the abdominal cavity. The fluid that forms typically is thick and bright yellow in colour and contains a lot of protein. However, other diseases (including some liver diseases and cancers) can also cause a similar fluid accumulation.

FIP can affect any organ of the body and so other forms of FIP (often termed ‘dry’ FIP) involve the formulation of granulomas (masses of virus and inflammatory cells) and the signs will vary according to the organ affected. This inflammation affects the eyes in around 30% of cases and the brain in around 30% of cases, but can also affect almost any tissues in the body including the liver, kidneys, lungs and skin. Thus, a wide range of signs may be observed including neurological disease (e.g., a wobbly and unsteady gait or fits), bleeding in the eyes and other vague signs of disease that may occur with lesions in the liver, kidneys or other internal organs.

Although FIP can occur in cats of any age, it is most often seen in young cats. Around 80% of cases diagnosed are in cats less than 2 years old, and many cases are seen in kittens around 4-12 months old. FIP is also more common in cats kept in groups or colonies (especially breeding households) as this is an environment where FCoV infections are spread easily. A crowded environment may also contribute to stress, which can be a factor in disease development as it compromises the cat’s immune response. There is evidence that genetics can also play a role in susceptibility to disease, although this is complex. Many cats that develop FIP are now in single cat homes, despite coming from multi-cat environments.

FIP is a very difficult disease to deal with because there are no clinical signs that are specific for the diagnosis of FIP, and no simple blood test to confirm a diagnosis. FIP may be considered more likely when:

None of these blood changes are specific for FIP, occurring with other diseases too, but if multiple changes are seen in combination with appropriate signs, a diagnosis of FIP becomes more likely. Many of these abnormalities may also not be present in the early stages of the disease but may become evident as the disease progresses. Thus, some tests that give normal results may have to be repeated later.

If fluid is present in the abdomen or chest cavity, obtaining a sample of the fluid and analysing the cell and protein content can be extremely helpful. With FIP the fluid invariably has a high protein content and further analysis of cell types and types of protein present can be useful. Further tests on fluid can be performed to look for the virus (PCR for example). Looking for fluid is an important part of investigating a cat for FIP so xrays, and particularly ultrasound, can be very helpful and again may need to repeated later as the disease progresses.

Other tests that can also sometimes be helpful include:

Looking for the presence of antibodies against the virus in a blood sample (coronavirus serology) is of very limited value – antibodies against FCoV develop when a cat meets coronavirus – this does not mean they have or will get FIP. A very large number of perfectly healthy cats are therefore positive on this test, and it should not be used for diagnosis.

To confirm a diagnosis is very difficult, but in general finding the typical type of effusion or inflammation and finding the virus in the same areas can be useful. Ways to look for the presence of the virus include immunocytochemistry and immunohistochemistry (staining the virus so it can be detected) and PCR (testing for the viruses genetic material). These tests can be performed on fluids, needle samples, biopsies and other samples. Remember, it is not enough to find just the virus as cats without FIP may have coronavirus, we must put together the puzzle of clinical signs, imaging findings fluid and needle samples and virus detection tests.

There have been significant recent developments in the management of this once fatal condition. Recent research by Professor Niels Pedersen of University of California, Davis, has shown that some newer anti-viral drugs such as GC-376 and GS-441524, used in humans against some emerging viruses, may be effective. Additionally, remdesivir, a prodrug of GS-441524 has become available legally in the UK and Australia. The drug has been used to treat human viral infections including SARS-CoV-2 (COVID-19). Initial experience has been positive with response rates of around 80% and therefore we have reason to be optimistic. The treatment remains expensive and requires a long course of treatment (84 days) so veterinarians should be mindful of commitment and cost involved plus potential for relapse. We look forward to learning more about the treatment of FIP over the next few years. Black market products remain available, but of unknown content and safety so legal drugs should be selected for the treatment of FIP in cats.

A commercial vaccine is available in some countries to help protect against FIP. However, this vaccine (while showing some efficacy) can only be given to kittens over 16 weeks of age. The major indication for using such a vaccine would be in breeding households, especially with a history of FIP, but by the time a kitten can be vaccinated (at 16 weeks) they would almost invariably have already been exposed to FCoV infection and so the vaccine probably has little or no value.

FIP is least common in household pets. The risk can be minimised by obtaining cats from a source with relatively few cats and by keeping cats in small stable groups (less than five cats in a household).

In breeding catteries, eradicating coronavirus infections is extremely difficult, as the virus is so ubiquitous, and it is unsuitable in most situations to attempt this. A more practical approach is to use measures to reduce the risk of FIP occurring, but recognising that on occasions, this may happen even in the best run catteries. Good practice to minimise the risk of FIP would include:

Wherever FIP occurs is a problem in a group of breeding cats:

Cause

The disease results from a viral infection called coronavirus causing wide-spread and severe inflammation in the body. The resulting inflammation can cause organ failure, fevers unresponsive to antibiotics, and in many cases, an accumulation of thick yellow fluid in the chest or abdomen.

Feline infectious peritonitis is an aberrant reaction to infection with the feline coronavirus. The feline coronavirus is quite common; most cats that become infected develop a mild gastrointestinal illness and recover uneventfully. The cats that develop the disease called FIP do so likely because their particular intestinal virus mutates in a way that allows it to penetrate other bodily tissues; also, their body’s response to the viral infection is inappropriate. Because there is no currently available test to distinguish between the “normal”, mild intestinal form of feline coronavirus, and the mutated one (studies are ongoing), it can be very difficult to confirm the diagnosis of FIP.

Feline coronavirus is common in cats, especially cats that are in crowded situations like shelters or breeding facilities. The disease is spread from cat to cat through contact with feces in shared litterboxes or on surfaces.  After exposure, some cats will shed active (infective) virus for weeks to months. Cats in multi-cat households can become re-infected. Some of the infected cats in the house will have no sign of disease; others may have mild gastrointestinal illness while one may come down with the severe form of the disease called FIP. In many cases, families are unaware that one or more of their cats have feline coronavirus.

FIP can occur at any age but is more common in cats less than one year of age when their immune system is not fully functional. Other reasons for immune compromise can also predispose to the development of the disease. Crowding, like that seen in shelters and catteries, is a common factor, but any source of stress can increase risk. There are genetic factors that predispose certain cats to FIP (often purebred) and make other cats resistant to infection.

Clinical Signs

There are different ways in which FIP manifests. With the wet or effusive form of FIP, the patient develops fluid in the chest or abdomen that seriously interferes with breathing and normal organ function. Patients with the wet form of the disease are gravely ill and survival is sadly measured in days to occasionally weeks. Cats with the dry form do not develop fluid in their body cavities but have insidious signs of illness such as fever and weight loss. These patient’s signs can wax and wane over months or even years. Both forms are eventually fatal. FIP is a disease that is unique to cats; no other species of animal is at risk of disease after exposure to feline coronavirus.

Diagnosis

If a cat is suspected of having FIP, tests will be done to search for other diseases that may play a role in immune compromise, as well as other sources of the symptoms. There is no effective therapy for FIP; this fact strongly motivates veterinarians to search for other potential causes for cats that are suspected of having the disease. Identifying the virus (through DNA identification) outside of normal gastrointestinal tissues, especially in cats with the characteristic type of inflammation associated with it called pyogranulomatous inflammation, is considered confirmatory.

Treatment

Although there is no therapy that will prevent death in patients with FIP, there are some therapies that may slow the progression of the patient’s decline.

Some patients will respond to steroids that reduce inflammation such as prednisolone and some chemotherapy medications. These medications carry some risks but may allow for short term improvement in the quality of life and survival.

Removing the effusion, particularly when it is in the chest cavity, will make cats feel better temporarily. The length of time this will help varies widely, from hours to weeks depending on the patient.

An experimental oral medication called polyprenyl immunostimulant has been found to slow progression in cats that have the DRY form of FIP. Sadly, this immunostimulant has no beneficial effect on cats with the wet or effusive form of FIP.

There are no other therapies that have been found to be beneficial for the treatment of FIP at this time. It is important to know that multiple studies into both prevention and therapy are ongoing at multiple institutions, and therapeutic treatments are awaiting FDA trial.

When a cat is suspected of having FIP, it is logical to be concerned about the other cats in the house. Because of genetic predispositions, if there is a blood-related cat in the house, there is more cause for concern. Absent any additional stressors, like overcrowding or compromised immune systems, the remaining cats in the house do not have a higher risk of development of FIP than any other cat in the general population. There is no need or benefit to sanitizing the home environment because all cats living together are exposed to feline coronavirus, but only some come down with FIP.

Prognosis

Both the wet and the dry form of FIP are eventually fatal, but patients with the dry form sometimes enjoy a long survival with the help of the new immunostimulant. Patients with the wet form can sometimes have short term relief with medications and interventions, but sadly, most succumb to the disease within days to weeks of diagnosis.

Long Term Follow-Up

Feline infectious peritonitis (FIP) is an important disease of domestic cats. It occurs worldwide in cats of all ages, but the disease is most common in young cats less than two years of age. Although FIP is not a particularly common disease, it is important because once a cat develops the disease, the outcome is almost invariably fatal.

FIP is associated with a viral infection called feline coronavirus. There are many different strains of feline coronavirus, which differ in their ability to cause disease. Previously there had been an attempt to classify these strains as either feline infectious peritonitis virus strains (capable of causing the FIP disease) or feline enteric coronavirus strains (essentially harmless strains mainly found in the intestinal tract). It is now recognized that feline enteric coronavirus strains can mutate (change) to the more harmful type of virus and cause FIP.

Diagnosing FIP is very challenging for many reasons. Unfortunately, there are no laboratory tests available that can distinguish between the enteric coronavirus and the FIP-causing strains. Even when infected with known FIP-causing strains, many cats do not develop FIP disease. The factors determining why one cat becomes diseased while others remain unaffected are unclear. FIP remains one of the least understood of all cat diseases.

Many cats (up to 50% in single cat households and as high as 80-90% in multi-cat environments) become infected with one or more strains of feline coronavirus at some time in their lives. The majority of cats with feline enteric coronavirus (about 90% or more) remain healthy. The incidence of feline infectious peritonitis disease is low (only 5 to 10% of infected cats and less than 1% of cats admitted to veterinary hospitals).

FIP appears to be more common in cats that live in multi-cat households, shelters, or catteries. Cats that are stressed due to re-homing, have recently had surgery, or have concurrent infections (more than one infection at a time) may also be more susceptible to developing FIP. Genetic factors are also thought to contribute to the development of FIP. Male cats  are affected more often  than females  Pure bred cats including Abyssinian, Bengal, Birman, Himalayan, Ragdoll and Devon Rex may be more predisposed to developing FIP.

Most cats become infected with feline coronavirus through the fecal-oral route (oral contact with infected feces). It is estimated that about one-third of these cats shed the virus in their feces. Most cats only shed the virus for a few months, but a small percentage will shed the virus continuously for life. Although the virus is quite fragile and does not survive for more than 24-36 hours in the normal environment, it is believed that cold temperatures may preserve the virus for months. Transmission on clothing or other objects is only likely within a few hours of contact.

As explained above, most infections are with relatively harmless strains of feline coronavirus. Unfortunately, this initial benign infection may later mutate to cause FIP in some cats. Even with the more harmful strains, apparently healthy cats may be carriers of the virus, and may shed the virus without ever showing signs of disease. Many cats that develop FIP have no history of contact with other cats showing clinical signs of FIP. The virus can remain dormant or inactive in the body for months to years before the cat eventually develops disease.

It is believed that most cats are exposed to feline coronavirus at a very young age, perhaps during the first few weeks of life. Most cats that develop FIP are between the age of 3 months and 2 years of age, although any age cat can develop the disease.

Many of the clinical signs of FIP are vague and occur with other diseases found in cats, making FIP particularly difficult to diagnose. There may be abnormalities in a routine blood analysis, but none is specific for FIP. X-rays may be helpful to determine the presence of fluid in the abdomen or chest. If fluid is present, some of it can be removed by tapping the chest or the abdomen. Analysis of this fluid at a veterinary laboratory can be particularly valuable, as few other diseases produce the same type of fluid that FIP creates. Nevertheless, fluid analysis does not always provide a definitive diagnosis of the disease. Sometimes FIP is a diagnosis of exclusion, meaning that a variety of similar conditions have been ruled out. The diagnosis may be further complicated because FIP may exist at the same time as some other conditions such as feline leukemia virus diseases. See the handout “Feline Infectious Peritonitis Testing” for further information on diagnosing FIP.

Currently the only way to make a positive diagnosis of FIP is by histological examination of affected tissue (or by post-mortem examination) by a pathologist at a laboratory. If there is any doubt about the diagnosis, your veterinarian may advise that a biopsy be taken from your cat, so that FIP can be distinguished from another disease.

Veterinary laboratories provide tests that detect antibodies to feline coronavirus in the blood, but these tests are non-specific and cannot be used alone to diagnose FIP. Some laboratories provide tests such as polymerase-chain reaction (PCR) tests, which can detect very small amounts of the virus but no unique genetic sequence associated with FIP has been identified. Although some of these tests claim to be able to distinguish between the strains, and to detect strains more likely to be associated with FIP, many independent experts disagree with these claims. Therefore, a positive test in a healthy cat is not a strong predictor of subsequent FIP disease.

If a cat has clinical signs consistent with a diagnosis of FIP then a positive test is supportive of the diagnosis, but not conclusive. Likewise, a negative test in the presence of advanced signs does not rule out the diagnosis of FIP.

As you can see, FIP is one of the most challenging diagnoses for your veterinarian to make because of the complexity of the disease and the limitations of current tests.

FIP is fatal in almost all cases. Supportive treatments may extend longevity and improve quality of life, however, there is no specific cure. Anti-inflammatory drugs such as corticosteroids (e.g., prednisolone) in combination with certain drugs that suppress the immune system (e.g., cyclophosphamide), may temporarily reduce inflammation and improve the cat's quality of life. While experimental treatments are being investigated, there are no commercially available and legally approved medications to treat FIP in the United States. For the clinically ill cat, once FIP has been diagnosed, euthanasia may be the most humane and appropriate course of action.

A newer anti-viral medication called Remdesivir was legalized in 2021 for treatment of FIP in the United Kingdom .  This medication is given as a series of injections over many weeks has been used with more success so far than traditional treatment. There are other medications currently in development for FIP treatment. Talk to your veterinarian about the latest options for FIP treatment.

In recent years, some manufacturers have developed vaccines to help in the prevention of FIP. Because the method of transmission and the sequence of events leading to clinical FIP disease are poorly understood, and because infection may have occurred before vaccination, the success of vaccination is not certain. Currently the vaccines for FIP are not recommended for general use. You and your veterinarian can discuss whether vaccination is appropriate for your cat.

If your cat has FIP, other cats in your household may be at a greater risk for becoming infected with feline coronavirus. Fortunately, infection will lead to this fatal disease in a minority of cats. As a precaution, many veterinarians recommend that you wait about a month after an infected cat dies before introducing a new cat into the house, to minimize the chance of exposure to the virus. In a multi-cat household in which an infected cat has died, it is recommended to wait at least three months to see if any other cats develop clinical disease. However, these previously exposed cats could be carriers of the disease and could potentially infect any new cats.

Cleaning with dilute bleach (1:32) is adequate to kill the virus. Keeping adequate numbers of litter boxes can also help minimize exposure to other cats’ feces.

Feline infectious peritonitis (FIP) is the name given to a common and aberrant immune response to infection with feline coronavirus (FCoV).[5]

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,[6] 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). However, many aspects of virus–host interactions affecting the disease remain uncertain, such as the factors that influence disease form (wet or dry), outcome (death or resistance), and host susceptibility.[7]

There is a lack of evidence FIP (Feline infectious peritonitis) is transmissible from cat to cat although it may explain rare mini-outbreaks of FIP.[8] 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.[9] 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.[10] 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.[11] Another major form of spreading is grooming or fighting. When an infected cat grooms a healthy cat, they leave their contaminated saliva on the fur. Later, when the healthy cat goes to groom themselves, they ingest the contaminated saliva and then become infected.[12]

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.[citation needed]

The hallmark clinical sign of effusive FIP is the accumulation of fluid within the abdomen or chest, which can cause breathing difficulties. Other symptoms include lack of appetite, fever, weight loss, jaundice, and diarrhea.[citation needed]

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.[citation needed]

Diagnosis of the effusive form of the disease has become more straightforward in recent years. Detection of viral RNA in a sample of the effusion (liquid drained from body), such as by reverse transcription polymerase chain reaction (RT-PCR) is diagnostic of effusive FIP.[13][14][15] However, that does require that a sample be sent to an external veterinary laboratory. Within the veterinary hospital there are a number of tests which can rule out a diagnosis of effusive FIP within minutes:

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:[16]

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 which compared various commercially available in-house FCoV antibody tests,[19] 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.

Because FIP is an immune-mediated disease, treatment falls into two categories: direct action against the virus itself and modulation of the immune response.

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.[20]

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.[21] 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.[22]

Antivirals (in the narrow sense) act by interfering with the enzymes or other biological processes in the FIP virus.

An experimental drug called GS-441524 was used in a field experiment of 31 cats. After 25 days, five cats had died, eight had been cured and subsequently relapsed, and 18 had been cured without any subsequent relapses. The eight who relapsed were treated again, some with higher doses. Of these eight, one died and seven were cured, meaning that 25 of the 31 cats were ultimately cured of FIP. Although the drug is not yet (as of 2019) commercially available in the United States, this study is considered very promising and may lead to commercially available medication for the treatment of FIP.[23] GS-441524 is available at >99% purity commercially from research chemical suppliers such as Selleckchem,[24] MedKoo[25] and MedChemExpress.[26]

An experimental antiviral drug called GC376 was used in a field trial of 20 cats: 7 cats went into remission, and 13 cats responded initially but relapsed and were euthanized. This drug is not yet (as of 2017) commercially available.[27]

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

Immunosuppressive drugs dampen the immune system, helping to reduce inflammation. The go-to immunosuppressive drug in FIP is prednisolone, a corticosteroid. There are no placebo-controlled trials showing prednisolone to be better than other anti-inflammatories.[28]

There is no effective vaccine against FIPV. DNA vaccination with plasmids encoding FIPV proteins failed to produce immunity.[29] Rather, it was observed that antibodies to the FIPV spike protein exacerbate the disease.

Kittens are protected from infection by maternally derived antibody until weaning, usually around 5–7 weeks of age; therefore, it is possible to prevent infection of kittens by removing them from sources of infection.[30] However, FCoV is a very contagious virus and such prevention does require rigorous hygiene.

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.[31][32] The film received an award at the 2018 Garden State Film Festival in the Narrative Short category[33] and was a Gold Kahuna winner at the 2018 Honolulu Film Awards.[34]