Feline Infectious Peritonitis
Feline infectious peritonitis (FIP) is an invariably fatal viral disease that is fortunately rare in cats. FIP is caused by a mutated form of the feline enteric coronavirus (FeCV). FeCV is a relatively common virus that many cats have been exposed to; however, a cat who is infected with FeCV may show no signs of disease at all. In most cases, there is a mild fever and short course of diarrhea associated with FeCV infection. FeCV is thought to be spread via inhalation or ingestion of contaminated feces or saliva. The lethal FIP syndrome is relatively rare in cats. Although it is not known what causes the relatively harmless FeCV to mutate into the virus capable of causing FIP, very young and very old cats seem predisposed to developing the lethal form of the disease.
When the mutation does occur, the virus becomes capable of infecting white blood cells in the cat, which allows the virus to spread to all body tissues. In some cases, even when this mutation has occurred, the cat will mount an effective immune response to the mutated virus and recover uneventfully from the infection. However, in some cases, the immune response is inadequate and the lethal form of the disease occurs.
In these cases, the disease is actually caused by the cat's immune response to the disease. Severe inflammation occurs throughout the body in response to the infection, and causes the clinical manifestation of FIP. There are two forms of FIP: an effusive, or wet form, which is more common, and a non-effusive, or dry form.
In the wet form, the cat typically accumulates lots of fluid within its abdomen and other body cavities, leading to a "pot-bellied" appearance. Eventually, this fluid builds up so much that it interferes with the cat's ability to breathe. The wet form is usually manifested more acutely; cats typically begin accumulating fluid very rapidly and may not survive more than a few weeks beyond this point. The dry form occurs more slowly, and signs usually consist of a persistent fever of unknown origin, weight loss, and signs related to the malfunction of other body systems. Sometimes the cat may show signs of liver dysfunction such as jaundice, or signs of kidney dysfunction such as increased water consumption and urination.
Unfortunately, there is not a very reliable way to diagnose this disease before death. A presumptive diagnosis of FIP can be made based on clinical signs and evaluation of body fluids and tissues. The most reliable methods are by analysis of the abdominal fluid or microscopic analysis of body tissues using histopathology. Once a presumptive diagnosis of FIP is made, the cat is only expected to live a few weeks to a few months. Therapy consists of draining the abdominal fluid (if present) to make the cat more comfortable and other supportive care. Immunosuppressive drugs are often used to try to calm down the body's immune response and lessen the severity of the symptoms.
Generally, cats who are live in crowded conditions, such as in catteries or shelters, are more likely to become infected with the lethal form of FIP, so prevention of overcrowding is an important step in maintaining an FIP-free colony. It is also very important to keep your cats healthy and maintain a clean environment. A vaccine is available, but its effectiveness has not yet been proven. Discuss with your veterinarian the best protocol for you to follow to keep your cats FIP-free.