The Effect of Natural Feline Coronavirus Infection on the Host Immune Response: A Whole-Transcriptome Analysis of the Mesenteric Lymph Nodes in Cats with and without Feline Infectious Peritonitis

Intestinal injury and vasculitis biomarkers in cats with feline enteric coronavirus and effusive feline infectious peritonitis

OBJECTIVE

To investigate intestinal injury, repair and vasculitis biomarkers that may illuminate the progression and/or pathogenesis of feline infectious peritonitis (FIP) or feline enteric coronavirus (FECV) infection.

MATERIALS AND METHODS

A total of 40 cats with effusive FIP (30 with abdominal effusion, AE group; 10 with thoracic effusion, TE group) and 10 asymptomatic but FECV positive cats (FECV group), all were confirmed by reverse transcription polymerase chain reaction either in faeces or effusion samples. Physical examinations and effusion tests were performed. Trefoil factor-3 (TFF-3), intestinal alkaline phosphatase (IAP), intestinal fatty acid binding protein (I-FABP), myeloperoxidase-anti-neutrophilic cytoplasmic antibody (MPO-ANCA) and proteinase 3-ANCA (PR3-ANCA) concentrations were measured both in serum and effusion samples.

RESULTS

Rectal temperature and respiratory rate were highest in the TE group (p < 0.000). Effusion white blood cell count was higher in the AE group than TE group (p < 0.042). Serum TFF-3, IAP and I-FABP concentrations were higher in cats with effusive FIP than the cats with FECV (p < 0.05). Compared with the AE group, TE group had lower effusion MPO-ANCA (p < 0.036), higher IAP (p < 0.050) and higher TFF-3 (p < 0.016) concentrations.

CLINICAL SIGNIFICANCE

Markers of intestinal and epithelial surface injury were higher in cats with effusive FIP than those with FECV. Compared to cats with abdominal effusions, markers of apoptosis inhibition and immunostimulation to the injured epithelium were more potent in cats with thoracic effusion, suggesting the possibility of a poorer prognosis or more advanced disease in these patients.

Feline Infectious Peritonitis: European Advisory Board on Cat Diseases Guidelines

Feline coronavirus (FCoV) is a ubiquitous RNA virus of cats, which is transmitted faeco-orally. In these guidelines, the European Advisory Board on Cat Diseases (ABCD) presents a comprehensive review of feline infectious peritonitis (FIP). FCoV is primarily an enteric virus and most infections do not cause clinical signs, or result in only enteritis, but a small proportion of FCoV-infected cats develop FIP. The pathology in FIP comprises a perivascular phlebitis that can affect any organ. Cats under two years old are most frequently affected by FIP. Most cats present with fever, anorexia, and weight loss; many have effusions, and some have ocular and/or neurological signs. Making a diagnosis is complex and ABCD FIP Diagnostic Approach Tools are available to aid veterinarians. Sampling an effusion, when present, for cytology, biochemistry, and FCoV RNA or FCoV antigen detection is very useful diagnostically. In the absence of an effusion, fine-needle aspirates from affected organs for cytology and FCoV RNA or FCoV antigen detection are helpful. Definitive diagnosis usually requires histopathology with FCoV antigen detection. Antiviral treatments now enable recovery in many cases from this previously fatal disease; nucleoside analogues (e.g., oral GS-441524) are very effective, although they are not available in all countries.

Feline Susceptibility to Leptospirosis and Presence of Immunosuppressive Co-Morbidities: First European Report of L. interrogans Serogroup Australis Sequence Type 24 in a Cat and Survey of Leptospira Exposure in Outdoor Cats

Leptospirosis is one of the most widespread zoonotic diseases and can infect both humans and animals worldwide. The role of the cat as a susceptible host and potential environmental reservoir of Leptospira is still not well understood, due to the lack of obvious clinical signs associated with Leptospira spp. infection in this species. This study aims to describe the first European detection of Leptospira interrogans serogroup Australis ST 24 in a young outdoor cat with a severe comorbidity (feline panleukopenia virus). In addition, the results of a preliminary study conducted in 2014-2016 are presented (RC IZSVE 16/12), which reports an investigation of Leptospira exposure of outdoor cats in Northeast Italy by means of serological investigation and molecular evaluation of urine. The animals included in the survey are part of samples collected during active and passive surveillance (diagnostic samples). The study reported a seroprevalence of 10.5% among outdoor cats and the serogroups identified were Grippotyphosa, Icterohaemorrhagiae, Bratislava, Canicola and Ballum. Symptomatic cats reported high MAT titres (ranging from 1:800 to 1:1600) towards antigens belonging to the serovars Grippotyphosa (1:800), Bratislava (1:1600), Icterohaemorrhagiae (1:200) and Copenhageni (1:200-1:800). In one subject, urine tested positive for Leptospira PCR. Cats with high antibody titres for Leptospira and/or positivity on molecular test suffered from immunosuppressive comorbidities (feline immunodeficiency virus and feline leukaemia virus; feline herpesvirus and lymphoma; hyperthyroidism). The overall prevalence of serum antibodies against Leptospira found in free-ranging cats (10.53%, 95% CI: 4.35-16.70%) and the identification of L. interrogans ST 24 in a young cat with immunosuppressive disease (feline panleukopenia virus) suggest the possibility of natural resistance to clinical leptospirosis in healthy cats. In a One Health perspective, further studies are needed to better define the pathogenesis of leptospirosis in cats and their epidemiological role as environmental sentinels or possible carriers of pathogenic Leptospira.

Fecal Feline Coronavirus RNA Shedding and Spike Gene Mutations in Cats with Feline Infectious Peritonitis Treated with GS-441524

As previously demonstrated by our research group, the oral multicomponent drug Xraphconn^® containing GS-441524 was effective at curing otherwise fatal feline infectious peritonitis (FIP) in 18 feline coronavirus (FCoV)-infected cats. The aims of the current study were to investigate, using samples from the same animals as in the previous study, (1) the effect of treatment on fecal viral RNA shedding; (2) the presence of spike gene mutations in different body compartments of these cats; and (3) viral RNA shedding, presence of spike gene mutations, and anti-FCoV antibody titers in samples of 12 companion cats cohabitating with the treated cats. Eleven of the eighteen treated FIP cats (61%) were shedding FCoV RNA in feces within the first three days after treatment initiation, but all of them tested negative by day 6. In one of these cats, fecal shedding reoccurred on day 83. Two cats initially negative in feces were transiently positive 1–4 weeks into the study. The remaining five cats never shed FCoV. Viral RNA loads in feces decreased with time comparable with those in blood and effusion. Specific spike gene mutations linked to systemic FCoV spread were consistently found in blood and effusion from treated FIP cats, but not in feces from treated or companion cats. A new mutation that led to a not yet described amino acid change was identified, indicating that further mutations may be involved in the development of FIP. Eight of the twelve companion cats shed FCoV in feces. All but one of the twelve companion cats had anti-FCoV antibodies. Oral treatment with GS-441524 effectively decreased viral RNA loads in feces, blood, and effusion in cats with FIP. Nonetheless, re-shedding can most likely occur if cats are re-exposed to FCoV by their companion cats.

Expression of Toll-like receptors 3, 7, 9 and cytokines gene expression in feline infectious peritonitis virus-infected CRFK cells and feline peripheral monocytes

Background

The role of Toll-like receptors (TLRs) in a feline infectious peritonitis virus (FIPV) infection is not completely understood.

Objectives

This study examined the expression of TLR3, TLR7, TLR9, tumor necrosis factor-alpha (TNF-α), interferon (IFN)-β, and interleukin (IL)-10 upon an FIPV infection in Crandell-Reese feline kidney (CRFK) cells and feline monocytes.

Methods

CRFK cells and monocytes from feline coronavirus (FCoV)-seronegative cats and FCoV-seropositive cats were infected with type II FIPV-79-1146. At four, 12, and 24 hours post-infection (hpi), the expression of TLR3, TLR7, TLR9, TNF-α, IFN-β, and IL-10, and the viral load were measured using reverse transcription quantitative polymerase chain reaction. Viral protein production was confirmed using immunofluorescence.

Results

FIPV-infected CRFK showed the upregulation of TLR9, TNF-α, and IFN-β expression between 4 and 24 hpi. Uninfected monocytes from FCoV-seropositive cats showed lower TLR3 and TLR9 expression but higher TLR7 expression compared to uninfected monocytes from FCoV-seronegative cats. FIPV-infected monocytes from FCoV-seropositive cats downregulated TLR7 and TNF-α expression between 4 and 24 hpi, and 4 and 12 hpi, respectively. IFN-β was upregulated early in FIPV-infected monocytes from FCoV-seropositive cats, with a significant difference observed at 12 hpi compared to FCoV-seronegative cats. The viral load in the CRFK and FIPV-infected monocytes in both cohorts of cats was similar over time.

Conclusion

TLR7 may be the key TLR involved in evading the innate response against inhibiting TNF-α production. Distinct TLR expression profiles between FCoV-seronegative and FCoV-seropositive cats were observed. The associated TLR that plays a role in the induction of IFN-β needs to be explored further.

The Population Diversity of Candidate Genes for Resistance/Susceptibility to Coronavirus Infection in Domestic Cats: An Inter-Breed Comparison

Feline coronavirus (FCoV) is a complex pathogen causing feline infectious peritonitis (FIP). Host genetics represents a factor contributing to the pathogenesis of the disease. Differential susceptibility of various breeds to FIP was reported with controversial results. The objective of this study was to compare the genetic diversity of different breeds on a panel of candidate genes potentially affecting FCoV infection. One hundred thirteen cats of six breeds were genotyped on a panel of sixteen candidate genes. SNP allelic/haplotype frequencies were calculated; pairwise FST and molecular variance analyses were performed. Principal coordinate (PCoA) and STRUCTURE analyses were used to infer population structure. Interbreed differences in allele frequencies were observed. PCoA analysis performed for all genes of the panel indicated no population substructure. In contrast to the full marker set, PCoA of SNP markers associated with FCoV shedding (NCR1 and SLX4IP) showed three clusters containing only alleles associated with susceptibility to FCoV shedding, homozygotes and heterozygotes for the susceptibility alleles, and all three genotypes, respectively. Each cluster contained cats of multiple breeds. Three clusters of haplotypes were identified by PCoA, two clusters by STRUCTURE. Haplotypes of a single gene (SNX5) differed significantly between the PCoA clusters.