Feline infectious peritonitis

Feline infectious peritonitis (FIP) is a fatal, incurable disease that affects cats. It is caused by Feline Infectious Peritonitis Virus (FIPV), which is a mutation of Feline Enteric Coronavirus (FECV/FeCoV). Experts do not always agree on the specifics of FIP. However, the most common theory is that the normally benign FECV mutates into FIPV. The mutated virus has the ability to invade and grow in certain white blood cells, namely macrophages. The immune system's response causes an intense inflammatory reaction in the containing tissues. Fewer than 1 in 20 cats survive the contraction of this disease, however its incidence rate is roughly 1 in 5000 for households with one or two cats. [1]

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Transmission and infection

FECV is very common, especially in places where large groups of cats are kept together (animal shelters, catteries, etc). Cats become infected by inhaling or ingesting the virus. The most commonly cited transmission source is feces, although contaminated surfaces such as food dishes and clothing can transmit the virus as well.

Despite the prevalence of FECV, most infected cats do not develop FIP. Often exposure to FECV produces no clinical signs, but may cause a mild upper respiratory disease. Therefore, a cat without clinical signs may still be an FECV carrier and may pass the virus to another cat. In any cat infected with FECV there is a chance that the virus may mutate into the FIP causing form. This chance is increased for cats that are immune compromised including very young and very old cats. There is also thought to be a genetic component to susceptibility to viral mutation.

Signs

  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 are wet) and progresses more rapidly than the non-effusive form.

Effusive (wet)

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.

Non-effusive (dry)

Dry FIP will also present with lack of appetite, fever, jaundice, diarrhea, and weight loss, but there will not be an accumulation of fluid. Although typically a cat with dry FIP will show ocular or neurological signs. For example it may become hard to walk or stand up, the cat may become paralyzed over time. There could also be a loss of sight.

Diagnosis

The signs associated with FIP are often non-specific, which can cause diagnosis to be very difficult. A definitive diagnosis requires examination of affected tissues for the FIP virus. This is usually performed post-mortem, but can be performed via tissue biopsy. Histopathological examination of tissue samples is usually the cheapest and most reliable available diagnostic test. A PCR test is also available for use with fluid or certain tissue samples, however, its efficacy is currently being reviewed.

More commonly, a presumptive diagnosis is made based on clinical signs and evaluation of abdominal or chest fluid, if available. Fluid caused by FIP tends to be yellow in color and have elevated protein levels. Blood tests can also be performed to bolster a presumptive diagnosis by looking for coronavirus antibodies and elevated protein. Coronavirus titers are not considered diagnostic in and of themselves due to the ubiquity of FeCoV, but may be used in conjunction with clinical symptoms to make an FIP diagnosis. It is important to note that cats with higher titres of FCoV are no more likely to develop FIP than those with lower titres. Cats with no exposure to FCoV cannot develop FIP.

Treatment

As there is no cure for FIP, treatment is symptomatic and palliative. Typically the owner is advised to make the cat as comfortable as possible until it becomes clear that the cat is suffering. Prednisone or other immunosuppressive drugs prescribed by a veterinarian may help to prolong the cat's life for a few weeks or months, but may be contraindicated in certain cases due to concomitant infection(s). Effusive FIP usually progresses too rapidly for any meaningful therapy to be attempted.

Quarantine is not necessary as FIP is not truly an infectious disease. Feline Enteric Coronavirus is shed in the feces and can be passed on to other cats, however, it is the mutated form of the virus that leads to FIP. This form is only found in macrophages and is therefore not shed and not contagious.

As FIP signs can be easily overlooked, it is highly advised to have your cat examined by a licensed vet at any signs of chronic diarrhea, unusual lethargy or respiratory infection. While treatment will only be symptomatic, it may prolong the life of the cat as well as soften the blow to the owner.