Diagnosis of feline infectious peritonitis using the cell tube block technique - a pilot study

Feline infectious peritonitis (FIP) is caused by a feline coronavirus (FCoV) and it is one of the most important viral diseases of cats. Recently, new drugs have been developed and used to face the inexorable fatal prognosis of FIP when untreated. More than ever, a definitive ante-mortem diagnosis is crucial to identify the cats that would benefit from antiviral treatment and to avoid euthanasia of unaffected animals. Identification of FCoV in macrophages using immunohistochemistry (IHC) is the gold standard method for diagnosing FIP. In this pilot study, the role of IHC applied to cell tube blocks (CTBs) of effusion fluids of cats clinically suspected to have FIP was assessed. A prospective cohort of seven cats was enrolled. IHC results in CTBs was positive in six out seven cases. Necropsy, histology and IHC in organs/tissues confirmed FIP infection in all the seven cases. The false negative in a CTB corresponded to a case of bacterial peritonitis secondary to FIP. As proof-of-concept, CTBs are valuable as a non-invasive technique for a definitive ante-mortem/clinical diagnosis of FIP and it is recommended to obtain CTBs from effusion fluids of all suspected FIP cases.