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

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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-017-0467-9) contains supplementary material, which is available to authorized users.

Feline morbillivirus in Northern Italy: prevalence in urine and kidneys with and without renal disease

“…One additional cat not affected by FIP (IHC negative on all organs) tested positive on nRT-PCR for FCoV. Indeed, viral systemic spread is not uncommon in FCoV-infected cats not affected by FIP (Porter et al, 2014;Barker et al, 2017).…”

Inflammatory Mediators in the Mesenteric Lymph Nodes, Site of a Possible Intermediate Phase in the Immune Response to Feline Coronavirus and the Pathogenesis of Feline Infectious Peritonitis?

“…A post-mortem examination was performed on each cat with owner consent and samples of MLN were collected into RNAlater Ò (Qiagen, Hombrechtikon, Switzerland) within 2 h of euthanasia and stored at À80 C until use. The Bristol cases form part of the University of Bristol FIP Biobank built up as a resource for multiple studies; many of these cases were utilized previously (Porter et al, 2014;Barker et al, 2017).…”

“…With reference to the sequence used in the original paper, the mutations in question appear to be at positions 1,048 and 1,050 rather than 1,058 and 1,060 as previously described, and will be referred to subsequently by the former numbers. Following initial FCoV RT-qPCR, all positive samples not analysed for previous studies by Porter et al (2014) or Barker et al (2017) underwent additional conventional RT-PCR and Sanger sequencing targeting the S gene region of interest. PCR was performed using the previously published degenerate primers (Porter et al, 2014).…”

“…A second switch from serine (S) to alanine (A) at amino acid residue 1,060 (S1060A) distinguished tissue-associated FCoV in a further small subset of FIP cases from FCoV shed with the faeces by healthy cats (Chang et al, 2012). These mutations have since been associated with systemic spread of FCoV, rather than providing proof of virulence (Porter et al, 2014;Barker et al, 2017;Felten et al, 2017a), so the two forms are subsequently referred to here as 'systemic' and 'enteric' FCoV. Early experiments demonstrated that not all cats are susceptible to FCoV infection, even with known pathogenic strains (Pedersen and Boyle, 1980), indicating the importance of host genetic factors/immune mechanisms in disease development. More recently it was shown that cultured monocytes from different cats vary in their ability to sustain viral replication, again suggesting that there is a subset of animals who can resist disease (Dewerchin et al, 2005;Tekes et al, 2010).…”

Differential susceptibility of macrophages to serotype II feline coronaviruses correlates with differences in the viral spike protein

“…Intriguingly, this characteristic difference also mapped to the membrane-proximal S2 part of the S protein. Though the biological significance of this difference, particularly its possible effect on the viral monocyte/macrophage infection phenotype, is still unknown, further studies indicated it to relate to systemic spread of the virus in the infected animal (Barker et al, 2017;Porter et al, 2014). The identification of this characteristic difference between the serotype I FCoV pathotypes in the C-terminal part of the S protein, the very part to which we earlier mapped the macrophage tropism in the serotype II viruses, prompted us to try to identify the critical tropism determinant(s) in these latter viruses.…”