Feline infectious peritionitis (FIP) is a common and often fatal disease in cats under 2 years of age. Caused by mutation of feline coronavirus (FCoV) in a small percentage of cats that are infected by this common and usually benign GI virus, it is distinct from human COVID-19 virus.
Cats infected with FIP initially develop nonspecific signs such as loss of appetite, weight loss, depression, and fever. In the “dry” form of the disease, affected cats often exhibit neurologic signs including seizures and ataxia (abnormal or uncoordinated movements). Those cats with the “wet” form of FIP accumulate fluid within body cavities, including the abdomen and the chest cavity. Affected cats may develop a pot-bellied appearance due to abdominal fluid accumulation, and if fluid accumulation is excessive, it may become difficult for an affected cat to breathe normally.
Unfortunately, these clinical signs can be seen in a variety of other diseases, making a definitive diagnosis of FIP challenging in many cases. Early diagnosis is important, though, because the best outcomes occur when treatment is started early in the FIP disease process.
To aid in a more rapid diagnosis, the American Association of Feline Practitioners, working in collaboration with the Every Cat Health Foundation, recently released new diagnostic guidelines for veterinarians.
Diagnosis still starts with a thorough physical examination and history of clinical signs and is supported by the results of basic and advanced imaging, bloodwork, antibody testing, culturing of fluid samples, and specific molecular biologic (genetic) testing to identify the causative virus in fluid, blood, and tissue samples.
The fact that many, if not most, cats have been exposed to FCoV, and that current tests cannot distinguish between the benign form of the virus and the FIP form, complicates diagnosis. Despite this, a presumptive diagnosis can be made by identifying a constellation of findings in many cases. Not surprisingly, for example, cats with FIP generally exhibit much higher antibody levels to coronavirus than healthy cats carrying the FCoV coronavirus.
Ongoing research focused on a more definitive diagnostic test, including the cutting-edge genetic screening work of Dr. Gary Whittaker at the Cornell University College of Veterinary Medicine (funded, in part, by the Cornell Feline Health Center) holds promise of dramatically improving our ability to diagnose this dreadful feline disease.
Journal of Feline Medicine and Surgery (2022) 24, 905–933, DoI: 10.1177/1098612X221118761