Cat sitting on a table getting a check from the vet.

Feline Infectious Peritonitis

Feline infectious peritonitis (FIP) is a unique viral disease of cats, unique in that the actual organ damage resulting from infection is not directly caused by the virus itself, but from the immune response to the invader.

The FIP organism is classified as a coronavirus, belonging to same group of viruses that cause gastrointestinal disease in dogs. Cats actually can be infected with two types of coronavirus: the feline enteric coronavirus and the feline infectious peritonitis coronavirus. Although the former can cause severe gastroenteritis in affected cats, most cases are subclinical; that is, there are no apparent clinical signs caused by the infection.

The importance of these enteric coronaviruses is not only that their presence in a feline can interfere with some standard testing procedures designed to diagnose FIP but also that the FIP coronavirus may actually be a mutation of the enteric coronavirus. If this is true, then all cats could be at risk of this disease.

Cats less than 4 years and over 12 years of age seem to have a higher preponderance for this disease than do other age groups. Inhalation or ingestion of infective secretions and excretions is the primary way in which this highly contagious disease is spread from cat to cat. The virus can even be passed via the uterus from an infected queen to her kittens.

Interestingly, most cats that contract this potentially deadly viral disease rarely show signs of infection, and may actually eliminate the infection soon after exposure occurs. If they are to appear, clinical signs usually show up 2 to 3 weeks after exposure, although this can vary by months to years. Upper respiratory signs can appear for a few days, then subside without any further problems until other clinical signs appear years later.

Another interesting fact about cats infected with FIP is that many are also concurrently infected with the feline leukemia virus. Since the leukemia virus suppresses the immune system, this paves the way for clinical FIP if exposure occurs.

FIP infections are unique in that the actual virus itself does not cause specific damage to the body’s organs or tissues. It is the cat’s exaggerated immune response to the virus that damages the organs, tissues, and blood vessels within the body. Clinical signs that are seen depend on where this damage is done. Almost all affected cats run persistent, low- grade fevers. Insidious weight loss and appetite loss are common as well.

Clinical FIP presents itself in three forms:

  1. Wet or effusive FIP
  2. Dry or noneffusive FIP
  3. A combination of forms 1 and 2

Wet FIP. When the immune system attacks the blood vessels in response to FIP, wet FIP results. Fluid that leaks out of the damaged vessels accumulates within the chest and/or abdomen, causing nonpainful abdominal distension and/or breathing difficulties.

Dry FIP. With dry FIP, many small nodules and regions of inflammation appear in various areas of the body, including the gastrointestinal tract, the lungs and heart, the brain and spinal cord, the kidneys, and/or the eyes. Obviously, with so many organ systems potentially affected, a wide variety of clinical signs, including coughing, vomiting, diarrhea, seizures, and blindness, can result.

In an effort to diagnose a suspected case of FIP, a veterinarian will rely initially on clinical signs seen, physical exam, blood samples, and perhaps microscopic examination of any abnormal fluids within the chest or abdomen. A persistent nonresponsive fever in a cat may point to FIP infection. As mentioned, diagnosis of the FIP coronavirus using certain tests designed to detect antibodies to FIP can be obscured by the presence or absence of the enteric coronavirus.

Unfortunately, there are no effective treatments that can eliminate the FIP virus from the feline body. Modulating the immune response with steroids and certain chemotherapy drugs can help provide temporary relief from clinical signs, but will do nothing to afford a cure. Survival time for cats exhibiting clinical signs can vary from days to weeks, depending on the degree of organ involvement.

Because of the lack of an effective treatment, prevention is the key with this disease. A vaccine is available for FIP. Also, owners should take alternative steps to protect their cats from the deleterious effects of this disease. Because FIP can gain a foothold in cats with unhealthy immune systems, it is important to keep the immune system in top-notch shape. This includes keeping cats on a good plane of nutrition and being sure that they are current on their feline leukemia vaccinations. Keeping cats indoors, restricting their interaction with stray felines, is another excel- lent way to limit potential exposure. Finally, all new cats brought into a household should test negative for the feline coronavirus.

Enteric Coronavirus (EC)

As a disease entity itself, EC can cause fever, vomiting, and diarrhea in kittens; however, if supportive care is provided, the gastrointestinal tract of these kittens usually recovers in a few days. Yet, the primary importance of this virus is not in the disease it causes, but in the confusion it often generates when trying to diagnose a case of feline infectious peritonitis.