Viral Diseases In Cats : Part 3

FELINE INFECTIOUS PERITONITIS 

Feline enteric coronavirus (FeCV) is a common disease of wild and domestic cats that is caused by a member of the coronavirus group. The disease is spread from cat to cat, but requires close and continuous contact with infective secretions. The incubation period is two to three weeks or longer, but 75 percent of cats exposed experience no apparent infection. Among those who do, a mild respiratory infection, with a runny nose or eye discharge, is the most common sign.

Cats who recover from mild infection can become asymptomatic carriers. Most cats who have been infected in this way are not immune to future infections with the coronavirus. It is estimated that 30 to 40 percent of all cats are positive for antibodies to FeCV, with that rising to 80 to 90 percent in catteries.

Fewer than 1 percent of all exposed cats will develop the secondary fatal disease known as feline infectious peritonitis (FIP). Why some cats develop FIP and others do not is not known for sure. It is believed that FIP is a mutation of the benign coronavirus and is therefore not contagious. The virus may change from benign to virulent weeks, months, or even years after the initial exposure to the coronavirus. Factors that seem to play a part in the change from benign to virulent are a genetic predisposition, exposure to chronic shedding of the virus, and living in a multicat environment, which could mean more stress. 

Genetic susceptibility is polygenic. One study suggested that Persians and Birmans have an increased incidence, but other studies say Abyssinians, Bengals, Birmans, Himalayans, Ragdolls, and the Rex breeds are especially at risk. Pedigreed cats, in general, do seem to be at higher risk, but that may relate to the fact that they are often housed in catteries. 

It is known that FIP tends to most often affect kittens, cats between 6 months and 2 years of age, and cats older than 14 years of age. Neonatal FIP has been implicated as a cause of fading kittens . There is a higher rate of infection in catteries, where conditions are apt to be crowded and there is greater opportunity for continuous and prolonged exposure. Cats who are poorly nourished, run-down, or suffering from other illnesses, such as feline leukemia, are most susceptible. These factors may lower the cat’s natural resistance to FIP. 

Despite its name,  FIP is not strictly a disease of the abdominal cavity. The virus acts on capillary blood vessels throughout the body—especially those of the abdomen, chest cavity, eyes, brain, internal organs, and lymph nodes. Damage to these minute blood vessels results in loss of fluid into tissues and body spaces. FIP tends to run a prolonged course. It may go on for weeks before signs are evident. The immune system of the infected cat plays a part in the disease. Cats have both cell-mediated and humoral (antibody) immunity. In cats with FIP, the system backfires and normal cells are targeted for destruction.

FIP occurs in two forms—wet and dry—both of which are invariably fatal.

Wet form early signs are nonspecific and mimic several other feline disorders. They include loss of appetite, weight loss, listlessness, and depression. The cat appears to be chronically ill. As fluid begins to accumulate in the body spaces, you may notice labored breathing from fluid in the chest or abdominal enlargement from fluid in the abdomen. Sudden death may occur from fluid in the heart sac. Other signs that accompany the wet form are fever up to 106°F (41°C), dehydration, anemia, vomiting, and diarrhea. Jaundice and dark urine are caused by liver failure.

Dry or disseminated form early signs are similar to those of the wet form, except fluid is not produced. The disseminated form is even more difficult to diagnose. It affects a variety of organs, including the eyes (15 percent of cases affect the eyes only), brain, liver, kidney, and pancreas. Sixty percent of dry form cases will show eye or brain involvement, or both. 

At surgical exploration, which may be necessary to make the diagnosis, sticky mucus or strands of fibrous protein may be found on the surface of the liver, spleen, or intestines. Previously, 10 to 20 percent of cats with the dry form were also infected with the feline leukemia virus. With more testing and control of FeLV that number is down to less than 5 percent.

The diagnosis of FIP can be suspected based on typical clinical signs along with an abnormal blood count, liver function tests, and an abnormal serum protein pattern. Analysis of peritoneal (chest) fluid, if present, is helpful. Serologic blood tests to detect coronavirus antibodies are not always conclusive and can lead to false positive interpretations. So far, no tests are consistent in identifying titers due to the benign presence of the virus, the virulent virus, or vaccination antibodies. The only certain way to confirm the diagnosis is by organ biopsy. In the wet form, fluid aspirated from the chest or abdomen may be highly suggestive of the diagnosis.

Treatment: 

Unfortunately, once a cat develops signs of secondary disease (either the wet or dry form), he will die. The wet form is worse, with cats often dying within two months. Cats with the dry form may have up to a year of good quality life. The cat can be made more comfortable by using medications; life may be prolonged with chemotherapy drugs such as cyclophosphamide or immunosuppressive doses of cortisone. Interferon and vitamin supplementation, especially vitamin C, can be helpful. Some cats do well with low-dose aspirin to reduce inflammation. Pentoxifylline (Trental) is being used by some veterinarians to treat the damage to blood vessels.