RNA in-situ hybridization for pathology-based diagnosis of feline infectious peritonitis (FIP): current diagnostics for FIP and comparison to the current gold standard

Abstract

Feline infectious peritonitis (FIP) is a systemic disease of cats caused by a highly pathogenic variant of feline coronavirus, or FCoV. Two distinct genotypes of FCoV exist (also referred to as serotypes): Type 1 viruses constitute the vast majority of FIP cases, while type 2 viruses are responsible for the remaining infections. Immunohistochemistry (IHC) currently serves as the gold standard for diagnosis of FIP; however, IHC is limited by variations in sensitivity. RNA in situ hybridization (RNA ISH) has an established foothold in infectious disease diagnostics and presents a potentially improved method for detection of FIP. This proof-of-concept study evaluated the efficacy of RNA ISH probes targeted to FCoV, as compared to IHC using monoclonal antibody FIP 3-70. Formalin-fixed paraffin-embedded tissues from FIP-positive cats were used for ISH, with the presence of RNA determined chromogenically. ISH tissue slides were then compared to their IHC counterparts, with efficacy determined based on metrics including staining intensity and abundance. Positive ISH staining on tissue was found to be both more intense and abundant than for IHC, suggesting that ISH serves as a highly sensitive method for the detection of FCoV/FIP in comparison to IHC - a finding that awaits further validation.