What is Feline Infectious Peritonitis (FIP)?

Despite years of research, there is still a lack of definitive diagnostic tests for FIP

While many feline guardians are familiar with the viruses Feline Leukemia Virus (known as FeLV) and Feline Immune Deficiency Virus (known as FIV or Feline AIDS), a very elusive, yet fairly common virus known as Feline Infectious Peritonitis (FIP) can also dramatically affect the health of infected cats leading to serious illness and often death.

Unlike the more common FeLV and FIV infections where testing is fairly straightforward, with FIP there still remains a lack of definitive diagnostic tests in detecting this infection, despite years of research. While many cats with what is called the “wet form” of FIP will often present with abdominal fluid/distention or chest fluid and difficulty breathing. The fluid has a characteristic straw-colored appearance and can be tested by most laboratories for virulent FIP virus to confirm the diagnosis. However, with the other common form known as the “dry form” of FIP, diagnosis is much more difficult.

Symptoms of the dry form of FIP are very general and nonspecific and can include just about any chronic sign of illness, especially general symptoms of weight loss, fever and inappetence. The fever is not typically responsive to antibiotics, given the viral cause. If the digestive tract is affected, thickened bowel loops as well as periodic or chronic vomiting or diarrhea can occur, as well as localized symptoms of the nervous system and eyes. FIP is a type of virus known as a corona virus in cats, of which there are many types, most of them often not causing any illness or disease.

Despite decades of research, the blood testing for antibodies to the corona virus FIP is not specific for the dangerous variant of this corona virus, and many tests can show up as false positives or negatives. The only way of definitively diagnosing this disease (when no fluid is present in the chest or abdomen) is for a biopsy to be completed of the affected tissues. There is also recent thinking that the many types of corona viruses that cats may carry may change or mutate into the more virulent disease causing FIP to form when under certain conditions of emotional or physical stress. It is believed to also form following simple surgical procedures like spaying or neutering, and in situations of crowding, giving shots or vaccinations and poor nutrition. The disease is highest in pure breed cats, although any breed can be affected.

The active disease seems to be most common in cats under one year of age, although there is also a spike in incidence in older cats, whose immune systems are more delicate. Many cats can be hidden carriers of all sorts of corona viruses, including the FIP strain. However, there is no way of predicting which cats will become clinically affected in the future. Treatments to date have yielded very poor results.

Vaccination developed back in the 1990s has not performed well in the field in my opinion, and there is some evidence that vaccinating cats may in fact predispose them to worse symptoms of disease, if they should later contract the actual FIP corona virus.

Feline Infectious Peritonitis (FIP) is one virus that needs to always be on our differential list of causes of chronic disease symptoms mentioned above. However, there remains much research to be done by the veterinary profession, both in terms of accurately diagnosing this viral disease, as well as in treating it; which to date has been very unrewarding.


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