FELINE INFECTIOUS PERITONITIS (FIP)

Feline Infectious Peritonitis is a syndrome that results from wide-spread infiltration of the body’s organs with inflammatory tissues called “pyogranulomas.” The resulting global inflammation leads to failure of the infiltrated organs, fevers unresponsive to antibiotics, and often the accumulation of thick yellow fluid in the abdomen or chest. The “wet” form of FIP, includes the effusion of thick, yellow fluid. The “dry” form leads to death over a much longer period (often years). Both forms usually have 100% mortality.

FIP is a rare disease, although it is fatal. It is seen more often in cats less than 2 years of age and older than 10 years of age. Multiple cat households, along with cats that spend time outdoors, are most susceptible. The virus that causes this disease is spread by respiratory secretions and feces. Litter that is contaminated with the virus is easily trapped on a cats fur, which is ultimately swallowed when the cat grooms. Cats infected with FeLV also are more at risk of developing this disease.

This disease is the subject of considerable controversy regarding diagnosis and treatment. This is partially due to the environmental situation that cats are placed in that causes undue stress on their immune systems, along with the complicated and variable immune response they develop when potentially faced with this virus. Like many cat diseases, FIP mimics other cat diseases, so a diagnosis in many cases does not come easily.

Risk factors for this disease are multiple cat households, the presence of normal cats that shed coronavirus, and the development of FIP susceptible cats in the general cat population. The continual infection and reinfection of cats with coronavirus in multiple cat households increases the chance of an individual cat developing FIP. Any cat infected with a corona virus has the potential of developing FIP. To give you some perspective on the current situation, 30% of household cats and up to 90% of cattery cats carry the coronavirus. Multiple cat households might be more susceptible due to increased stress, crowding, poor sanitation, parasites, and other diseases like the FeLV and the FIV.

Initially there are no or minimal symptoms after exposure. Some cats might show mild upper respiratory signs (sneezing) or diarrhea, but are so mild that they can go unnoticed. When serious symptoms do appear, the signs might be sudden in the younger cats, or more gradual in older cats.

Cats that have dry form have vague symptoms that come and go, and can affect many different systems in the body. They might be lethargic, have poor appetites, weight loss and look ill. Common organs involved are the eyes, central nervous system (brain and spinal cord), and internal organs like the liver and kidney. Other symptoms could include seizures, paralysis, behavior changes, poor vision, increased sensitivity to touch, and urinary incontinence.FIP positive cats may also have an ongoing fever. It might wax and wane, and usually does not respond to antibiotics.

Since many different organs can be involved with the dry form, the symptoms we see with this form of FIP can mimic other common diseases of cats, like hyperthyroidism, liver disease, sugar diabetes and kidney disease. Other diseases like inflammatory bowel disease, cancer, and toxoplasmosis might also have similar symptoms.

Pets with the wet form of the disease may have breathing difficulty or distended abdomens, in addition to some of the symptoms of the "dry form". The onset of these symptoms is faster than the gradual symptoms noted in the dry form. The wet form of FIP is much easier to diagnose than the dry form.

The virus can also infect the brain or spinal cord. This form of the disease can sometimes be diagnosed by an eye exam. Changes can be noted in the back of the eye, especially the retina.

No, FIP is not contagious

Feline Infectious Peritonitis is a reaction to infection with feline coronavirus. Most cats who become infected with feline enteric coronavirus essentially get the flu and never develop anything serious. Some cats, however, react with this devastating syndrome.

Here are some basics about this virus:

• It is common wherever cats are housed in groups and it is readily transmitted between cats.
  
  
• Transmission is typically by contact with infected feces. This means that the litter box is the usual place where infection takes place. This infection is unusual in cats that free-roam outdoors (no litter box) or who live in homes where there is only one cat. The virus enters the new host’s body via the nose and mouth.
  
  
• An active infection lasts several weeks to a few months. The virus is shed in the infected cat’s stool during this period. If the cat is reinfected, the virus sheds again for weeks to months. During this time, the cat may or may not seem ill. Some infected cats do not shed the virus.
  
  
• Households with fewer than 5 cats eventually spontaneously clear of coronavirus. Households with more than 5 cats virtually never clear of coronavirus.
  
  
• Most household disinfectants readily kill coronavirus immediately. Room temperature kills coronavirus within 48 hours. Carpeting is protective to the virus and the virus is able to survive in carpeting for at least 7 weeks.
  
  
• Once a cat has been infected with the virus and recovered, the cat can be easily re-infected by continued exposure to infected feces. In this way, many catteries where there are always cats sharing litter boxes never rid themselves of this infection.
  
  
• The enteric coronavirus attacks intestinal cells and creates GI upset. As long as the infection is confined to the GI tract, the cat will not get FIP.
  
  
• The process of immunological defeat of the virus involves a cell called a “macrophage.” The macrophage consumes infected material, packaging it in special structures which it floods with acids and digestive enzymes. Any virus is killed by this process and its components are then used by the immune system to help mount a specific immunological reaction. In some cats, a mutation occurs in the coronavirus. This mutation occurs during infection and allows the virus to survive the treatment by the macrophage. Instead of being killed by the macrophage, the virus essentially uses the macrophage to hitch a ride into the body’s core. The macrophage response mounts in an attempt to kill the virus but ends up producing large numbers of ineffective macrophages and immunologic proteins which make up a special immunologic tissue called a “pyogranuloma.” FIP is basically the infiltration of normal organs with pyogranulomas.
  
  
• The mutation to a form of virus that can cause FIP is more likely to occur in a cat with an immune-compromised state. Most cats with FIP are under age 1 year. Crowding is also an important source of immune-compromise.

We do not know why. We can inject fluids from a cat with FIP into a normal cat and cause FIP. However, other than this kind of experimental transmission, the mutated virus doesn’t seem to occur in the natural external secretions of an infected cat. This effectively confines the mutated virus inside the sick cat’s body, though the FIP positive cat will still shed the non-mutated virus.

We used to think that the difference between getting the “flu” and getting FIP was all about the strain of the virus with which a cat gets infected. FIP results, as described above, from a mutation that occurs in the virus after infection has occurred. Whether or not this mutation occurs seems to relate more to the immune status of the cat than any factor in the virus. The more virus there is replicating, the greater the chance of mutation occurring. Having an immature or suppressed immune system means the possibility of more virus replication.

The mutation isn’t the same every time. There are two viral genes and the mutation pretty much always involves at least one of them but the mutation can occur in any number of places within either of these two genes. There are currently too many possible mutations to develop a meaningful test.

Diagnosis is difficult in many cases, particularly in the dry form. We do not have a blood test that tells us if the virus is present like we have with FeLV and FIV. The test we do have tells us if antibodies have been made to the category of virus that FIP belongs to (coronavirus), but it does not tell us if it is the actual FIP virus or not. There are DNa type tests available that are more specific in making this diagnosis, the most common one being the polymerase chain reaction (PCR) test. As we generate more data on this test in sick cats its usefulness will probably increase.

In addition to specific FIP antibody or DNa tests, blood samples, X-rays and fluid analysis are also used, and are utilized especially in cats that have the wet form. The only way to be 100% certain of the diagnosis is to biopsy one of the abdominal lymph nodes, the kidneys, or the liver.

At this time the diagnosis of FIP is “clinical.” This means that there is no positive or negative test; the doctor must look at several findings. These are some of the findings combined with the physical examination and history findings that lead to a diagnosis of FIP

• Elevations in Total Protein and Gamma Globulins
  Total serum protein is a simple value that can be checked in virtually every animal hospital in a matter of minutes. Cats with FIP commonly have very high serum protein levels. The type of protein that elevates in FIP is basically antibody levels of assorted types. If a blood panel is checked on a cat with FIP, serum protein is often divided into albumin and globulin amounts (adding these together provides the “total protein” level.) When protein levels are broken down into these two groups, it will be the globulin level that is elevated. In particular, it is the “gamma globulin” levels that are elevated.
  
  
• The Albumin to Globulin Ratio
  FIP tends not only to elevate globulin levels but it also tends to decrease albumin levels. Albumin is an important carrier protein in the blood and one’s body tends to conserve it at all costs. Albumin can be lost through glomerular disease, protein-losing enteropathy, or it can be under produced by a failing liver. All these conditions can occur with FIP. If the albumin to globulin level is less than 0.8, there is a 92% statistical chance that the cat has FIP.
  
  
• The FIP Titer
  This test is often included on a feline blood panel and reflects a cat’s circulating antibody level against coronavirus. The problem is that exposure to coronavirus is common in cats and is not particularly meaningful in diagnosing FIP. Further, cats with fulminant FIP may not be producing FIP antibodies and have negative titers. The only time such a titer might be useful is if one is screening a healthy cat for coronavirus; in this event a negative titer would indicate that the cat will not be shedding virus and can be introduced into a coronavirus free living situation. Many breeders strive for coronavirus-free catteries and such screening is important. The test is not helpful in diagnosing FIP in a sick cat, however.
  
  
• Testing the Belly/Chest Fluids
  FIP classically produces a clear but viscous yellow effusion, usually in the belly but possibly in the chest or in both locations. The fluid typically has a total protein level greater than 3.5 mg/dl. Several efforts to find a diagnostic test that could be performed on this fluid have been made. It is controversial whether or not an FIP antibody titer in the effusion fluid is of significance.

The fluid that builds up in the wet form of FIP is called ascites when it occurs in the abdomen, and pleural effusion when it occurs in the thorax. The fluid is sticky and usually light yellow to golden color, with a relatively large amount of protein.

• “Rivalta’s Test”
  This is a test with which few veterinarians are familiar but it can be very helpful in the diagnosis of FIP. A test tube is filled with distilled water and one drop of 98% acetic acid is added. To this mixture one drop of effusion is added. If the drop dissipates, the test is negative. If the drop retains its shape, the test is positive. A negative Rivalta’s test is 97% accurate in ruling out FIP. A positive test is 86% accurate in ruling in FIP.
  
  
• PCR Testing
  PCR testing is an extremely sensitive method for detecting DNA, in this case coronavirus DNA. The advantage it has over traditional antibody titers is that it distinguishes active virus infection from past exposure. At least at this time, PCR testing cannot distinguish mutated FIP-causing virus from regular coronavirus.
  
  
• Immunofluorescent Coronavirus Staining of the Effusion
  In this test the effusive fluid is tested immunologically for presence of coronavirus using antibodies tagged with fluorescent dyes. In a study using a large number of cats, there were no false positives meaning that if this test is positive there is a 100% confirmation that the cat has FIP. Unfortunately, if the test is negative that does not mean the cat does not have FIP (only 57% of negatives did not have FIP).
  
  
• X-Rays can also be very helpful in diagnosing the wet form of FIP which presents itself as ascites.

• Ultrasound gives us additional information on the internal organs, especially if they are surrounded by fluid.

• Tissue Biopsy
  Most FIP cats are too sick for surgery, though sometimes flushing away the belly effusion surgically provides a “rally” of improvement temporarily. A tissue sample is the best method for confirming FIP as there are few conditions that create pyogranulomas throughout the body but if regular biopsy is equivocal, tissues can be stained for the presence of coronavirus and only in FIP will there be enough coronavirus within macrophages for positive staining. A positive tissue stain is 100% accurate in confirming FIP

In many FIP cases, especially the dry form, the only way to confirm the diagnosis is to biopsy an internal lymph node or internal organ, and look for specific microscopic changes that occur in FIP. This biopsy can be performed on a live cat during an exploratory surgery, or during a necropsy (the animal version of an autopsy) in a dead cat.

Common organs to biopsy are the liver and kidney. In addition, the mesenteric lymph node (remember the ultrasound above where it was enlarged?) is a good organ to biopsy.

There is no treatment that will cure this disease. Over the years many different treatments have been attempted to alleviate symptoms of this disease. Some of them seem to work for variable periods of time, so they are worth trying in some cases. These include antibiotics, antinflammatories, immune system stimulators, and vitamins. Since it is difficult to confirm the presence of this disease, especially in the dry form, it is worth the effort to treat your cat symptomatically. Unfortunately, the long term outcome is poor. Cats with confirmed cases of FIP usually succumb within a few months.

There are always experimental treatments. Here are some treatments that are being explored:

• Immune suppression
  FIP is a disease created by the cat’s own immune system. Immunosuppressive drugs such as prednisone and cyclophosphamide have been used to slow the progression of FIP.
  
  
• Removing the effusion
  Suctioning of the effusion will ease the difficulty breathing of a cat with fluid in its chest but even removing the effusion from the belly helps remove a large source of inflammation. Some cats experience a temporary improvement with the fluid removed.
  
  
• Antiviral Drugs
  Ribavarin was tested and not found to be helpful. Interferon alpha was tested and not found to be helpful when given as an injection and actually made infection worse when given orally. Feline Interferon gamma is being investigated.

Cats living in households that already had a cat die of FIP have a less than 5 percent chance of developing FIP, mostly because they have already been exposed to the virus and fought it off. Siblings of cats that died of FIP have a greater chance of developing the problem. The most important factor in controlling FIP is limiting the number of cats in a house, preferably to less than 5. In addition, good nutrition, good veterinary care, and good sanitation, will go along way to preventing this problem.

Wait at least one month before introducing a new cat to house that had a cat die of FIP. Cleaning the litter pan often and preventing litter from tracking throughout the house may be helpful. The virus can live in the environment for several weeks, so clean as thoroughly as possible using a 1:32 dilution of household bleach. Remove all cat related products that can not be thoroughly cleaned.

If there are only one or two surviving cats, the chances are that, in time, the virus will completely clear and they will stop getting re-infected. Surviving cats are felt not to have any higher risk over the general population for developing FIP from their coronavirus, though a littermate of the FIP cat might have a slightly higher incidence due to predisposing genetic factors.

Since this is not a contagious disease, one can argue that one does not need to wait before getting another cat. If one wants to see that there is no remaining coronavirus around the house leftover from the deceased cat, a 3 month period has been advocated. If there are surviving cats, one can periodically check FIP titers and wait for them to go negative before adding another cat if one wishes to avoid further passing around of coronavirus. The new cat can also be screened for an FIP titer. When one considers that only 5% of cats in multi-cat homes get FIP despite the incidence of exposure to coronavirus being as high as 80% in some studies, this may not be necessary.

Developing a vaccination has historically been fraught with difficulty simply because it is the immune response against the virus that causes the disease. How does one make a vaccine without creating the same immune response against the virus? Pfizer has developed the only FIP vaccine on the market by using a temperature sensitive mutant coronavirus. This virus is innoculated into the cat’s nose. The virus is incapable of spreading beyond the nose and throat because it cannot survive at body temperature. In the nose and throat, however, it generates a localized immune response that prevents a coronavirus from effectively entering the body. The effectiveness of this vaccine has been questionable and remains in controversy. The vaccine is given to cats over age 4 months of age and is thus not helpful in the chief situation where a vaccine could do the most good: the breeding cattery. Because most cats are not at risk for FIP infection and those that are, are at risk at an age too young for the vaccine, most veterinary teaching hospitals do not stock this vaccine.

The ideal candidate for vaccination would be an uninfected cat going to a cattery where litter box sharing is likely. This would seem to be an unusual situation but it might come up in these circumstances:

• A feral cat is moved into an indoor or shelter colony. (It is not unusual for FIV+ cats from feral colonies to be removed from the colony and put in a sanctuary for FIV+ cats).
• A cat from a single cat home is released to a rescue group goes to a foster home where there are a number of other cats already present.
• A cat moves from a single cat home to live in a multi-cat home.

Yes. Dogs and humans cannot get sick from feline coronavirus. The feline coronavirus is not involved in SARS (severe acute respiratory syndrome) though SARS is caused by a coronavirus.

The information in this summary was largely drawn from the following article: K. Hartmann. Feline Infectious Peritonitis. Veterinary Clinics of North America Jan 2005; 39-79.