Cat Guardians 101

What cats are at risk of developing FIP?

In domestic cats males and females are affected equally. Cats of any age can develop FIP, but as you would imagine, cats with the weakest immune system are most likely to develop FIP. This includes kittens, cats infected with FeLV (feline leukemia virus) and geriatric cats. The larger number of cases are in kittens and cats under two years of age, since this is the age they are most likely to first encounter FCoV. FIP remains fairly common in cats up to 5 years of age but there is a considerable decline in the incidence of the disease in middle age cats, and another spike as they reach old age, and their immune systems begin to decline.

In a cat under 2 years old, with a history of coming from a breeder or rescue shelter, FIP must be suspected when there are vague clinical signs, such as increased temperature (fever), being off food, failure to gain weight (as a kitten) or loss of weight (as an adult). In around half of the cats with FIP, an effusion (fluid) builds up in the abdominal or thoracic cavities.

Most cats who become infected with FCoV shrug it off as a mere annoyance: the virus goes to the gut, increases its numbers there, possibly causing diarrhea, then the cat’s immune system fights back and the virus gets thrown out of the body.  Feline infectious peritonitis (FIP) occurs when the cat is stressed and/or undernourished or when the cat is faced with overwhelming amounts of virus, such that the immune system hardly stands a chance.  Sadly these situations are all too common in breeding households and rescue shelters: overcrowding, concurrent diseases such as cat flu, and corner-cutting in nutrition all serve to stress the cat and make these places a hotbed of FIP.

The number of reported cases worldwide is unknown but some recent studies indicate the incidence rate is roughly one cat in 20 from ordinary pet households, but the virus infects about 90% of purebred and rescue shelter cats. FIP has been proven to be more common in certain breeds and lines. It appears to be more common in Bengals and Persians, for example, but it is unclear whether these breeds are more susceptible because of their genetics or whether they are exposed to FCoV more often since most of these cats live or come from breeding catteries.

Feline coronavirus (FCoV) the virus which causes Feline Infectious Peritonitis is a hard nut to crack. One who knows only too well is Diane D. Addie, Ph.D., BVMS, MRCVS who has been dedicated to researching FIP for decades. According to Dr. Addie, most cats simply become infected, shed FCoV for a month or two, mount an immune response, eliminate the virus and live happily ever after. However, for reasons that we don’t yet fully understand, instead of clearing the FCoV infection, an unfortunate few cats develop Feline Infectious Peritonitis. 

FIP is an immune-mediated disease and the name Feline Infectious Peritonitis is slightly misleading: FIP isn’t inflammation of the peritoneum (the lining of the abdomen): it is a vasculitis (inflammation of the blood vessels). The clinical signs which the cat develops depend on which blood vessels are damaged, and on which organ(s) the damaged blood vessels supplied.

What are the clinical signs of the disease?

There are two major forms of FIP. An effusive form often called “wet FIP” is characterized by high protein fluid accumulation in body cavities and a non-effusive form or “dry FIP” which is characterized by pyogranulomatous lesions in any body organ or system. Although FIP is separated into these two forms, there is really a gradient between these forms, and sometimes signs of both forms can be seen. Signs common to both forms of FIP include fluctuating antibiotic-resistant fever, lethargy, anorexia, and weight loss.

Effusive or wet FIP is caused by immune-complex damage to small blood vessels that permits leakage of plasma protein and fluid into body cavities. The wet form of the disease progresses rapidly and soon the cat may appear pot-bellied in appearance due to the fluid accumulation in the abdomen. Fluid may also accumulate in the chest causing respiratory difficulties. The fluid (effusion) characteristic of FIP is yellowish (straw color), sticky or mucinous, odorless, high in protein and containing numerous neutrophils and macrophages. Sadly, most cats with the wet form of FIP die within two months of onset of clinical signs.

Non-effusive or Dry FIP occurs in a considerable percentage of the cats with FIP. In dry FIP vascular damage may produce mild, subclinical effusion early in the course of the disease and generally the signs of the disease come on more slowly. Nonspecific signs such as chronic weight loss, fever, loss of appetite and lethargy appear. Kittens incubating FIP do not grow as well as their siblings. Any organ or system may be affected alone or in combination, which is why clinical signs are nonspecific to FIP (i.e., FIP can present like other diseases): the most consistent clinical feature of non-effusive FIP is its variability. The most common sites for lesions in cats with non-effusive FIP are the eyes, central nervous system, mesenteric lymph node, liver, and kidneys.

Ten to twenty-five percent of cats with dry FIP will develop neurological signs. When granulomas occur in the central nervous system, we see paralysis, disorientation, loss of balance, tremors, convulsions, behavior changes and urinary incontinence. Granulomas can also occur in the chest. Sometimes the eye is the only organ affected. The pupil may appear irregular and the eye may appear discolored because of the inflammation that is present. Some cats with the dry form can live a few years after first showing clinical signs.

Clinical signs of FIP vary significantly from case to case depending on the strain and load of virus involved, each cat’s immune system status as well as the organs and/or systems affected. In general, the wet form progresses much quicker than the dry form and in both scenarios the cat’s body condition takes a toll with the hair coat becoming rough or dull and the sick cat becoming increasingly lethargic and depressed.

Clinical signs of effusive or wet FIP:
Persistent and antibiotic unresponsive fever
Poor appetite
Lack of appetite
Weight loss (gradual)
Accumulation of fluid in the chest or abdomen cavities
Gradual swelling of the abdomen (appearing potbellied)
Breathing difficulties
Sneezing or runny nose

Non-effusive or Dry FIP
Persistent and antibiotic unresponsive fever
Poor growth in kittens
Ocular signs, inflammation of various parts of the eye(s)
Neurological symptoms (i.e., lack of motor skills/loss of ability to use hind legs, loss of vision, etc.)

What is Feline Infectious Peritonitis?
What causes Feline Infectious Peritonitis?

How do you reach the FIP diagnosis?
What are the treatment options for FIP?

What can you do to prevent FIP?
Grieving for the loss of your  FIP cat

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