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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 infectious peritonitis (FIP) is a systemic, potentially fatal viral disease. The objectives of this study were to review clinical and laboratory features and treatment of cats highly suspected of FIP in Wuhan, China. The clinical records of 127 cats highly suspected of FIP were reviewed for history, clinical signs, physical findings, and diagnostic test results. Sex, neutering status, breed, age, and month of onset of disease were compared with the characteristics of the clinic population. Age and neutering status were significantly correlated with FIP-suspicion. Sex, breed and onset month were not associated with FIP. There were many more FIP-suspected cases in cats in young cats or male intact cats. Effusion was observed in 85.8% of the FIP-suspected cats. Increased serum amyloid A (SAA) and lymphopenia were common laboratory abnormalities in the FIP cases. Furthermore, 91.7% of the cats highly suspected of FIP had an albumin/globulin (A/G) ratio < 0.6, while 85.3% had an A/G ratio < 0.5. The mortality rate for FIP-suspected cats was 67%, and six submitted cases were confirmed by FIP-specific immunohistochemistry. Of the 30 cats treated with GS-441524 and/or GC376, 29 were clinically cured. The study highlights the diverse range of clinical manifestations by clinicians in diagnosing this potentially fatal disease. A/G ratio and SAA were of higher diagnostic value. GS-441524 and GC376 were efficient for the treatment of FIP-suspected cats.

Feline infectious peritonitis (FIP) is a severe feline coronavirus-associated syndrome in cats, which is invariably fatal without anti-viral treatment. In the majority of non-effusive FIP cases encountered in practice, confirmatory diagnostic testing is not undertaken and reliance is given to the interpretation of valuable, but essentially non-specific, clinical signs and laboratory markers. We hypothesised that it may be feasible to develop a machine learning (ML) approach which may be applied to the analysis of clinical data to aid in the diagnosis of disease. A dataset encompassing 1939 suspected FIP cases was scored for clinical suspicion of FIP on the basis of history, signalment, clinical signs and laboratory results, using published guidelines, comprising 683 FIP (35.2%), and 1256 non-FIP (64.8%) cases. This dataset was used to train, validate and evaluate two diagnostic machine learning ensemble models. These models, which analysed signalment and laboratory data alone, allowed the accurate discrimination of FIP and non-FIP cases in line with expert opinion. To evaluate whether these models may have value as a diagnostic tool, they were applied to a collection of 80 cases for which the FIP status had been confirmed (FIP: n = 58 (72.5%), non–FIP: n = 22 (27.5%)). Both ensemble models detected FIP with an accuracy of 97.5%, an area under the curve (AUC) of 0.969, sensitivity of 95.45% and specificity of 98.28%. This work demonstrates that, in principle, ML can be usefully applied to the diagnosis of non-effusive FIP. Further work is required before ML may be deployed in the laboratory as a diagnostic tool, such as training models on datasets of confirmed cases and accounting for inter-laboratory variation. Nevertheless, these results illustrate the potential benefit of applying ML to standardising and accelerating the interpretation of clinical pathology data, thereby improving the diagnostic utility of existing laboratory tests.

Feline infectious peritonitis (FIP) is a lethal, viral-induced immune-mediated disease that remains a challenge for diagnosis and treatment in cats. Proteomic profiling, which analyzes the protein content of biological samples, offers the potential to identify novel biomarkers that could improve the diagnosis and management of FIP. This study aims to assess the serum proteome and identify proteins that differentiate healthy cats from cats diagnosed with effusive FIP using liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS). A total of 30 cats diagnosed with effusive FIP and 27 clinically normal cats were enrolled. Twenty-three proteins were significantly ( p  < 0.01, ≥ fivefold change in abundance) differentially expressed between cats with effusive FIP and controls. Among these, the P2X purinoceptor, DNA topoisomerase, Notch receptor 2, and cadherin-17 were identified as key proteins of interest in cats with effusive FIP. Our findings suggest that these differentially expressed proteins could serve as potential diagnostic biomarkers and therapeutic targets for FIP. However, further studies are needed to validate these findings and explore their potential applications.

Feline infectious peritonitis (FIP) is a fatal disease caused by feline coronavirus (FCoV), manifesting as effusive (wet) or non-effusive (dry) forms. Granulomatous lesions in the gastrointestinal tract, particularly the colon, are rare and pose diagnostic and therapeutic challenges. A 7-year-old castrated male domestic shorthair cat (4.1 kg) presented with anorexia and vomiting. Blood tests showed an albumin:globulin ratio of 0.5, a mild elevation in aspartate aminotransferase, mild leukocytosis, and a severe elevation of feline serum amyloid A. The abdominal ultrasound and computed tomography imaging showed a mass in the transverse colon and surrounding mesenteric lymph nodes. The mass was observed to be relatively well vascularized, with areas of low-density uneven necrosis. Histological examination revealed severe pyogranulomatous inflammation with macrophages, neutrophils, and lymphocytes predominantly present in both the affected colon and lymphoid tissues. Immunohistochemistry for feline infectious peritonitis (FIP) virus antigen of the lesion showed a strong positive result, confirming limited and localized lesion induction by FIP virus infection. The cat received GS-441524 for 12 weeks, resulting in clinical improvement, lesion resolution, and normalized lab results. RT-PCR and antibody tests were negative post-treatment. This case report describes a rare presentation of FIP virus infection, characterized by localized lesions confined to a specific segment of the colon. In this case, treatment with the nucleoside analog GS-441524 was very effective in improving the localized lesion and demonstrated excellent efficacy in clearing the FIP virus.

Feline coronavirus (FCoV) is a major pathogen causing feline infectious peritonitis (FIP), a lethal disease in cats, necessitating accurate diagnostic methods. This study developed and compared novel primers targeting the FCoV membrane (M) gene for enhanced detection. Specific primers were designed for the M gene and their performance evaluated using reverse transcription-PCR (RT-PCR), nested RT-PCR, and reverse transcription-quantitative PCR (RT-qPCR) on 80 clinical effusion samples from cats suspected of FIP. Specificity of assays was tested against other feline viruses, with sensitivity being assessed via serial dilutions of FCoV RNA. RT-qPCR had the highest sensitivity, detecting 9.14 × 101 copies/µL, identifying 93.75% of positive samples, followed by nested RT-PCR (87.50%, 9.14 × 104 copies/µL) and RT-PCR (61.25%, 9.14 × 106 copies/µL). All assays had 100% specificity, with no cross-reactivity to other viruses. The nested RT-PCR and RT-qPCR outperformed RT-PCR significantly, with comparable diagnostic accuracy. The novel primers targeting the FCoV M gene, coupled with RT-qPCR, delivered unparalleled sensitivity and robust reliability for detecting FCoV in clinical settings. Nested RT-PCR was equally precise and amplified diagnostic confidence with its high performance. These cutting-edge assays should revolutionize FCoV detection, offering trusted tools that seamlessly integrate into veterinary practice, empowering clinicians to manage feline infectious peritonitis with unprecedented accuracy and speed.

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.

Feline infectious peritonitis (FIP) is a systemic immune-mediated inflammatory perivasculitis that occurs in a minority of cats infected with feline coronavirus (FCoV). Various therapies have been employed to treat this condition, which was previously usually fatal, though no parameters for differentiating FIP recovery from remission have been defined to enable clinicians to decide when it is safe to discontinue treatment. This retrospective observational study shows that a consistent reduction of the acute phase protein alpha-1 acid glycoprotein (AGP) to within normal limits (WNL, i.e., 500 μg/mL or below), as opposed to duration of survival, distinguishes recovery from remission. Forty-two cats were diagnosed with FIP: 75% (12/16) of effusive and 54% (14/26) of non-effusive FIP cases recovered. Presenting with the effusive or non-effusive form did not affect whether or not a cat fully recovered (p = 0.2). AGP consistently reduced to WNL in 26 recovered cats but remained elevated in 16 cats in remission, dipping to normal once in two of the latter. Anaemia was present in 77% (23/30) of the cats and resolved more quickly than AGP in six recovered cats. The presence of anaemia did not affect the cat’s chances of recovery (p = 0.1). Lymphopenia was observed in 43% (16/37) of the cats and reversed in nine recovered cats but did not reverse in seven lymphopenic cats in the remission group. Fewer recovered cats (9/24: 37%) than remission cats (7/13: 54%) were lymphopenic, but the difference was not statistically different (p = 0.5). Hyperglobulinaemia was slower than AGP to return to WNL in the recovered cats. FCoV antibody titre was high in all 42 cats at the outset. It decreased significantly in 7 recovered cats but too slowly to be a useful parameter to determine discontinuation of antiviral treatments. Conclusion: a sustained return to normal levels of AGP was the most rapid and consistent indicator for differentiating recovery from remission following treatment for FIP. This study provides a useful model for differentiating recovery from chronic coronavirus disease using acute phase protein monitoring.

Feline infectious peritonitis (FIP), a devastating disease with near-complete mortality, is caused by the feline coronavirus (FCoV) and affects domestic cats worldwide. Herein, we report the development of a reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay incorporating xylenol orange (XO) as a visual indicator for FCoV detection. The assay employed six oligonucleotide primers targeting regions of the nucleocapsid (N) gene. Under optimized conditions (65 °C, 60 min), amplification products were detected through pH-dependent colour changes in the XO dye. The RT-LAMP-XO assay exhibited high specificity for FCoV, with no cross-reactivity against other common feline viral pathogens. While the detection limit (1.7 × 101 copies/µL) was an order of magnitude higher than that of qPCR, the method offered advantages in simplicity and speed compared to existing diagnostic approaches. Although less sensitive than qPCR, the RT-LAMP-XO assay may serve as a rapid screening tool when used in combination with additional primer sets. These findings demonstrate the potential utility of XO-based RT-LAMP as a simple, visual detection method for FCoV infection.

Feline panleukopenia, feline calicivirus infection, feline viral rhinotracheitis, and feline infectious peritonitis are significant diseases that threaten feline health. The trend of mixed infections is increasing, and current diagnostic methods are limited in scope and unable to provide rapid, simultaneous detection of these diseases. Four groups of primers and probes targeting the gene of Feline Panleukopenia virus (FPV), the gene of Feline Herpesvirus (FHV-1), the gene of Feline Calicivirus (FCV), and the gene of Feline Infectious Peritonitis Virus (FIPV) were designed. After optimizing the concentrations of primers and probes and annealing temperature, a quadruplex TaqMan MGB fluorescent quantitative PCR method was established to concurrently detect these four pathogens. Recombinant plasmid standards were constructed to establish standard curves, and the sensitivity, specificity, reproducibility, and clinical application of the assay were evaluated. The optimal final concentrations of primers for FPV, FHV-1, FCV, and FIPV were 0.08, 0.04, 0.06, and 0.12 μM, respectively, and the optimal final concentrations of probes were 0.08, 0.08, 0.12, and 0.12 μM, respectively. The best annealing temperature was 59°C. No cross-reaction was observed with common pathogens in infected cats. The minimal detection limits for recombinant plasmids of T-VP2, T-TK, T-ORF2, and T-N were 50.79, 53.21, 47.91 and 41.25 copies/μL, respectively. The R² values of standard curves are 0.994, 1.0, 0.998 and 0.999, respectively, and high amplification efficiencies of 105.05%, 96.28%, 98.82%, and 96.45%, respectively. The coefficient of variation for inter-batch and intra-batch tests ranged from 0.14 to 1.37%. Among 381 fecal samples from cats, the detection rates for FPV, FHV-1, FCV, and FIPV were 13.65% (52/381), 18.37% (70/381), 26.77% (102/381), and 9.71% (37/381), respectively, with a 100% agreement with previously reported methods and commercial kits. The sensitive, specific, high-throughput, quadruplex TaqMan MGB quantitative fluorescent quantitative PCR method was successfully established for the simultaneous detection of FPV, FHV-1, FCV, and FIPV.