Feline infectious peritonitis (FIP) is a fatal disease of cats caused by feline coronaviruses (FCoVs) found worldwide. In cats, the typically mild enteric FCoV can develop specific mutations where virus (often referred to as FIPV) then replicates in macrophages, a key change in the pathogenesis and development of FIP. These two biotypes, FCoV and FIPV, are almost identical in their genome. Because of this close similarity in genome, the biotypes cannot be differentiated by routine reverse transcriptase polymerase chain reaction (RT-PCR).

In cases of FIP, almost 10% of the cats develop neurological signs due to development of pyogranulomatous meningoencephalitis and meningomyelitis. Signs most commonly noted are ataxia, seizures, nystagmus, hyperesthesia and cranial nerve deficits. Along with neurological forms of the disease, manifestations of disease affecting the eyes may occur, appearing as uveitis or chorioretinitis. Because the median survival time of cats with FIP is 9 days and a FIP diagnosis usually leads to euthanasia of the patient, a reliable diagnostic test is important to be able to confirm the presence of the disease.

A confirmed diagnosis of FIP can be challenging even in cases where effusion is present and is especially difficult in non-effusive forms of the disease because confirmation requires histological examination of biopsy specimens of affected tissue. This diagnostic approach in cases with neurological FIP is limited and utilizing RT-PCR on blood samples to confirm diagnosis is often not useful because both sensitivity and specificity of RT-PCR is too low to allow definitive diagnosis or rule out FIP.

In this study, the goal was to determine sensitivity and specificity of a real-time RT-PCR in cerebrospinal fluid (CSF) to diagnose FIP in cats with or without neurological and/or ocular signs. Cats with confirmed cases of FIP were compared with control cats that had clinical signs similar to FIP but a confirmed diagnosis of another disease. The study was a prospective, case-control project that included 34 cats. Nineteen cats were definitely diagnosed with FIP by histopathology and 15 cats had other diseases but similar clinical signs.

The results showed that using real-time RT-PCR on CSF in this study, the specificity was 100%. While real-time RT-PCR has been known to give false positives results in serum and plasma, this did not occur with testing CSF fluid in this situation. The sensitivity was not as high, 85.7%, for real-time RT-PCR of CSF in cats with neurological and/or ocular signs. The authors feel that with the excellent specificity, real-time RT-PCR is a reliable tool for diagnosing FIP. If cats with only neurological and/or ocular FIP are evaluated, then the sensitivity of real-time RT-PCR on CSF is also high enough to where this may be an interesting tool for the diagnosis of neurological FIP. (VT)