What is Feline Infectious Peritonitis?

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FIP or Feline Infectious Peritonitis is an uncommon fatal disease in cats caused by the Feline Coronavirus (FCoV). It is a virus that attacks the cells of intestinal walls and causes diarrhea in cats. While FIP can be found in domestic cats as well as wild cats, it mostly occurs in places where a large number of cats are kept together, such as animal shelters, catteries, etc.


The disease, FIP is mainly of two forms – non-effusive (dry), and effusive (wet). The effusive is more common and spreads much faster than the non-effusive form. Although it is not a common disease in cats, it is vital to take preventive measures as once a cat develops the disease; the results are invariably fatal. Now, let’s have a detailed study on Feline Infectious Peritonitis (FIP) in cats.


What is FIP?


FIP or Feline Infectious Peritonitis is an immune-mediated disease observed in cats. It is caused by some strains of Feline Coronavirus. However, not all strains of Feline Coronavirus cause FIP. But some strains are capable of causing FIP by mutation of the virus or aberration of the immune response.



Those strains that are avirulent and do not cause FIP are termed Feline enteric coronavirus (FECV), whereas the virus strains that can mutate and cause FIP are termed Feline Infectious Peritonitis Virus (FIPV). Once a cat develops FIPV, the virus becomes more virulent, replicates faster, and transforms into a more hazardous form, posing a severe health risk to the cats.


The virus affects the White Blood Cells, Monocytes, present in the body of the cats, and then, these cells carry the virus throughout the entire body. The infected cells mainly reside in vital organs like the kidney, brain, or abdomen of the cats and lead to an intense inflammatory reaction.


The main reason behind the disease is the interaction of the immune system of the cat’s body with the virus. As soon as a cat is affected by the FIPV, the disease progresses rapidly, and the consequences can be fatal.


Unfortunately, the infected cats generally do not show any symptoms during the infection period, and there are no laboratory tests available that can differentiate between FECV and FIPV strains. However, proper antibodies can make the immune system strong and protect the cats from FIP.


Are certain breeds susceptible to FIP?



While cats of all ages and breeds carry this virus, it is most common in kittens of 5-7 weeks. The cat breeds that are more susceptible to FIP include Abyssinian, Himalayan, Ragdoll, Bengal, etc. Apart from these, cats that have undergone recent surgery or have concurrent infections are more likely to develop FIP.  It is also noticed that genetic factors of the cats may contribute to developing the disease.


How is FIP Transmitted?

The majority of cats get FIP through the fecal-oral path. Usually, the infected cats shed the virus through their feces. So, while sharing cat litter trays, if the uninfected cats swallow the feces or inhale the wastes, they may develop the disease. Most cats shed the virus for a couple of months; however, very few discard the virus continually for a lifetime.


The virus may also spread through different bodily fluids. Saliva is the most common form of transmitting the disease. When many cats share the same food, a healthy cat may get infected with the virus, as it comes in contact with the saliva of the infected cat. It may also happen during grooming or fighting. FIP may even get transmitted through direct contact between cats.


Types of FIP and its Symptoms:

The very first symptom of the FIP disease in a cat may be very vague. However, the most common clinical signs of the disease are lethargy, absent appetite, weight loss, fluctuating fever, and listlessness. The symptoms typically start to show up after a period of several days.



There are mainly two types of FIP viruses. They are as follows:

1. Effusive (Wet) FIP:

The most known sign of effusive FIP is that it causes breathing difficulties in cats because of the fluid accumulated within their thoracic cavities or abdomen. There are other symptoms such as jaundice, lack of appetite, fever, weight loss, and diarrhea. The consequences are fatal, and the effusive form of FIP spreads more rapidly than the non-effusive type.

2. Non-Effusive (Dry) FIP:

Non-effusive FIP also possesses similar symptoms as the effusive type, including jaundice, diarrhea, lack of appetite, fever, and weight loss. The only difference is that in this form of Feline Infectious Peritonitis, there occurs no fluid accumulation.


An affected cat will also show neurological or ocular signs, because they may develop severe inflammation in their organs like the brain, liver, eyes, intestine, etc. The cat may face difficulty in standing or walking and may become functionally paralyzed with time. This type of disease can even result in the loss of their vision, especially if not treated soon.


As evident, both types of disease are equally harmful. Once the FIP starts to develop, it deteriorates the health condition of the cat rapidly. Although some cats remain normal for a couple of weeks, in most cases, the unfortunate end result is death.


Diagnosis of FIP

FIP is very much difficult to diagnose because most of its clinical signs are indefinite and occur along with other diseases found in cats. A bit of abnormality may be noticed in the blood test analysis, but none of the anomalies is specific to FIP.


To ascertain the presence of fluid in the chest or abdomen area, X-rays may be beneficial. If the presence of fluid is detected, some of the liquid can be removed by tapping the cat’s abdomen or chest. Since there are other types of diseases as well that produce the same kind of fluid as FIP produces, you must test it in a veterinary laboratory to analyze the liquid properly. But it is to be noted that only fluid analysis does not provide a perfect diagnosis of the disease.


Another reason behind the complexity in the diagnosis of the disease is the simultaneous existence of FIP and other medical conditions like feline leukemia virus disease. Currently, the only way to make the correct and definite diagnosis of FIP is through histological examination of the affected tissue in a laboratory. The veterinarian may advise for a biopsy or autopsy of the cat’s tissue for proper diagnosis. The suitable diagnosing ways of FIP are as follows:


1. Diagnosis of Effusive (Wet) FIP:

Lately, the diagnosis of effusive FIP has become pretty straightforward and easy. Several tests can be performed in a veterinary laboratory to diagnose the effusive FPI within a few minutes.

  • If the total protein in the effusion is less than 35 g/L, FIP is highly unlikely.
  • In the effusion, if the albumin-to-globulin ratio is over 0.8, FIP is not present. However, if it is less than 0.4, there is a possibility of the occurrence of FPI, but it is not certain.
  • In case the cells in the effusion are mostly lymphocytes, then there is no need to diagnose FIP.

2. Diagnosis of Non-Effusive (Dry) FIP:

As the clinical signs of non-effusive FIP are more indistinct and varied, it is quite challenging to diagnose this type of FIP. Some of the criteria that are considered for the diagnosis of non-effusive FIP are as follows:

  • If the cat’s age is below 2 years, and it is purebred, then there is a high chance of the kitten having FIP. It is observed that in more than 70% of the cases, FIP exists in the pedigree kittens.
  • There is a possible existence of FIP if the cat experiences stress caused due to recent vaccination or neutering.
  • In case the cat shows up with clinical symptoms like eating less than usual, suffering from weight loss, having pyrexia, icterus, and intra-ocular troubles, it is likely to have FIP.
  • Without a rise in the liver enzymes, having an increase in the bilirubin count or hypergammaglobulinemia can be used to diagnose FIP.
  • The veterinarian performs hematology tests to detect non-regenerative, anemia, and lymphopenia for the diagnoses of FIP.
  • The veterinarian in the laboratory performs serology tests, which help in the detection of FIP in the cat’s body.


If the cat is seronegative, then a non-effusive or dry FIP diagnosis may be ruled out. To detect antibodies to FIPV, veterinary laboratories provide proper and efficient tests. Though these tests are unspecific, they alone can’t be used to diagnose FIP.


PCR or Polymerase-Chain Reaction Test is performed by some laboratories that detect a minute amount of the virus. Such antigen tests are claimed to differentiate between the strains associated with FIP. However, many experts often disagree with these assertations. Thus, it is evident that the complexity of the disease and the constraints of its corresponding clinical tests make the diagnosis of FIP in cats a really challenging task for veterinarians.



Treatment for FIP

In almost all cases, the result of FIP is fatal. Several supportive therapies are there that may extend the life span of the cats and improve their quality of life, but there is no absolute cure now.


Since Feline Infectious Peritonitis is an immune-mediated disease, the treatment can be done in two ways, as stated below.


1. Antiviral Drugs – Directly Treating the Virus: For the treatment of FIP, the commonly used antiviral drugs are either Human Interferon or Feline Recombinant Interferon Omega. These antiviral medicines directly act against the Feline Enteric Coronavirus dwelling in the cat’s body. As interferons are species-specific, Feline Interferon is more effective than Human Interferon. A few other antiviral drugs are GC 376 and GS-441524.


2. Immune Response Modulation: The other way to treat Feline Infectious Peritonitis is by modulating the immune response of the cat. Certain medicines exist that suppress the immune system and reduce temporary inflammation in FIP. One such immunosuppressive drug is Prednisolone.


Recently, an experimental drug named Polyprenyl Immunostimulant or PI is being examined for the treatment of a non-effusive (dry) form of FIP. The manufacturer of this investigational medicine is Sass and Sass and tested by Dr. Al Legendre.


Some anti-inflammatory medicines, such as corticosteroids, combined with other drugs like cyclophosphamide, can also suppress the cat’s immune system, decrease inflammation temporarily, and improve its quality of life. Besides, there are many herbal immune system boosters available that can fight against Feline Infectious Peritonitis. NHV Felimm – Natural Herbal Support is an all-natural drug that strengthens the weakened immune system of cats very fast.


The below chart shows some experiments of both immunosuppressive drugs and antiviral medicines on FIP-affected cats.

Type of Experimental Drug

Drug Name

Total No. of Cats

Total No. of Days

No. of Cats Died

No. of Cats Survived

Immunosuppressive drug
Polyprenyl Immunostimulant (PI)
Antiviral Drug



Nowadays, researchers are even investigating if a combination of both antiviral drugs and immune-suppressive medicines can treat Feline Infectious Peritonitis in cats more effectively and cure them eventually or not.



Prevention of FIP

Since Feline Infectious Peritonitis is incurable, it is always better to take prevention to avoid the development of this lethal disease in your cats. However, it must be noted that the preventions of FIP are not certain in any way. In this type of infection, the symptoms are indistinguishable at the beginning. As a result, it may happen that the cat might have gotten infected before taking the preventive measure.


However, as we all know that “Prevention is better than cure”, it is necessary to take a few preventive measures to be on the safer side. There are mainly two types of preventive measures, as mentioned below.


1. Vaccination:

An intranasal vaccine for the treatment of FIP is commercially available. The vaccine has modified- live mutant strains of coronavirus that are temperature-sensitive. It is recommended not to be used on kittens who are less than 16 weeks of age because experiments have not yet been performed on such young kittens to verify their protection from the disease. The said vaccine helps in averting the induction of high serum antibody levels, as these may promote ADE or Antibody-Dependent Enhancement of infectivity.


As little or no proper fact is known about the duration of immunity offered by the vaccine, many controversies regarding the vaccine persist. Though the vaccine is licensed for annual revaccination, the exact duration of protection has not yet been confirmed. Some studies show the effectiveness of the vaccine, while others show that there is little or no benefit from it. However, studies have concluded that the efficacy of the vaccine depends on several factors pre-infected cats with FIP forms of the disease, age, species, etc.


The vaccine is said to protect cats with no or low FCoV antibody concentration. However, this vaccination won’t work in the case of pre-infected cats. In a household environment, if there are known cases of Feline Infectious Peritonitis, this vaccine will not be effective. But, in circumstances where a healthy cat that has never suffered from FCoV is vaccinated before entering an FCov-endemic shelter, the vaccine may induce some level of protection.


2. Preventing FCoV Infection in Kittens:

The maternally derived antibodies protect the baby cats from the harmful effects of any deadly disease. However, those disappear usually between 5-7 weeks of age. Therefore, you must remove the kittens from the sources of infection and put them in a well-sanitized place to prevent the occurrence of FIP.


Also, you must use disposable litter boxes for your kittens to provide them with a germ-free environment. You can opt for SpeedySift Cat Litter Box with Disposable Sifting Liners to maintain the proper hygiene of your cat. As FCoV is a very infectious and contagious virus, maintenance of rigorous hygiene is necessary.



FIP or Feline Infectious Peritonitis is a fatal disease. If a cat is clinically affected by FIP, there is no specific cure. The diagnosis processes are also not certain and quite complicated. The only effective way is to perform euthanasia. But seeing your beloved pet die is the worst feeling a pet owner may experience. So, the best way to keep your cat safe from being affected by FIP is to maintain good hygiene and sanitation, take them to the veterinarian for regular checkups, and vaccinate them properly. If you follow this, you can prevent your cat from getting infected with any feline disease.

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