The emergence of severe acute respiratory syndrome 2 (SARS-CoV-2) has led the medical and scientific community to address questions surrounding the pathogenesis and clinical presentation of COVID-19; however, relevant clinical models outside of humans are still lacking. In felines, a ubiquitous coronavirus, described as feline coronavirus (FCoV), can present as feline infectious peritonitis (FIP)—a leading cause of mortality in young cats that is characterized as a severe, systemic inflammation. The diverse extrapulmonary signs of FIP and rapidly progressive disease course, coupled with a closely related etiologic agent, present a degree of overlap with COVID-19. This paper will explore the molecular and clinical relationships between FIP and COVID-19. While key differences between the two syndromes exist, these similarities support further examination of feline coronaviruses as a naturally occurring clinical model for coronavirus disease in humans.

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.

Feline infectious peritonitis (FIP) is a systemic disease of cats caused by a highly pathogenic variant of feline coronavirus, or FCoV (termed FIPV). Two serotypes of FCoV exist: type 1 viruses constitute 85% to 95% of FIP cases, while type 2 viruses are responsible for the remaining 5% to 15% of infections. Immunohistochemistry (IHC) currently serves as the gold standard for diagnosis of FIPV; however, IHC is limited by its wide 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 FIPV. This study evaluated the efficacy of RNA ISH probes targeted to FIPV, as compared to IHC using monoclonal antibody FIP 3-70. Formalin-fixed paraffin-embedded tissues from FIP-positive cats were used for ISH, with RNA presence 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/FIPV, in comparison to IHC.

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.