Limitations of using feline coronavirus spike protein gene mutations to diagnose feline infectious peritonitis

Emily N Barker,Anja Kipar,Angelica Stranieri,Séverine Tasker,Michael J Day,Andrew D Davidson,Emily L Porter,Chris R Helps,Toby Knowles

doi:10.1186/s13567-017-0467-9

Abstract

Feline infectious peritonitis (FIP) is a fatal disease of cats, and a sequela of systemic feline coronavirus (FCoV) infection. Mutations in the viral spike (S) gene have been associated with FCoVs found in tissues from cats with FIP, but not FCoVs found in faeces from healthy cats, and are implicated in monocyte/macrophage tropism and systemic spread. This study was designed to determine whether S gene mutation analysis can reliably diagnose FIP. Cats were categorised as with FIP (n = 57) or without FIP (n = 45) based on gross post-mortem and histopathological examination including immunohistochemistry for FCoV antigen. RNA was purified from available tissue, fluid and faeces. Reverse-transcriptase quantitative-PCR (RT-qPCR) was performed on all samples using FCoV-specific primers, followed by sequencing of a section of the S gene on RT-qPCR positive samples. Samples were available from a total of 102 cats. Tissue, fluid, and faecal samples from cats with FIP were more likely to be FCoV RT-qPCR-positive (90.4, 78.4 and 64.6% respectively) than those from cats without FIP (7.8, 2.1 and 20% respectively). Identification of S gene mutated FCoVs as an additional step to the detection of FCoV alone, only moderately increased specificity for tissue samples (from 92.6 to 94.6%) but specificity was unchanged for fluid samples (97.9%) for FIP diagnosis; however, sensitivity was markedly decreased for tissue (from 89.8 to 80.9%) and fluid samples (from 78.4 to 60%) for FIP diagnosis. These findings demonstrate that S gene mutation analysis in FCoVs does not substantially improve the ability to diagnose FIP as compared to detection of FCoV alone.

Highlights

Feline coronavirus (FCoV) infection is ubiquitous in domestic cats, with up to 90% of cats within multicat households being infected [1, 2]
Of the 25 cats excluded, five had no tissue samples collected into formalin, six had no tissue samples collected into RNAlater; and 14 only had limited tissue samples collected into formalin such that feline infectious peritonitis (FIP) could not be definitively diagnosed or excluded
Some studies have examined the use of FCoV RT-PCR alone in the diagnosis of FIP using fluid samples [29, 31]

Summary

Introduction

Feline coronavirus (FCoV) infection is ubiquitous in domestic cats, with up to 90% of cats within multicat households being infected [1, 2]. The majority of FCoV infections are asymptomatic or are associated with mild intestinal disease. An estimated 1 to 5% of infected cats develop feline infectious peritonitis (FIP) [3, 4], characterised by the development of a variable combination of pyogranulomatous polyserositis, vasculitis and granulomatous lesions in organs, and an extremely high mortality rate [5, 6]. Avirulent or self-limiting FCoV infection was believed to be confined to the intestines, but we know that healthy FCoV-infected cats can. There are two different serotypes of FCoV, both of which can cause FIP. There is worldwide geographical variation in the relative distribution of serotype 1 and 2, and co-infections can occur [12,13,14,15,16,17]

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