Feline infectious peritonitis. ABCD guidelines on prevention and management

A retrospective study of clinical and laboratory features and treatment on cats highly suspected of feline infectious peritonitis in Wuhan, China

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.

Mutation analysis of the spike protein in Italian feline infectious peritonitis virus and feline enteric coronavirus sequences

Feline coronavirus (FCoV) exists as two different genotypes, FCoV type I and II, each including two biotypes, feline enteric coronavirus (FECV) and feline infectious peritonitis virus (FIPV), the latter being a virulent variant originating from the former virus. Recently, two amino acid substitutions, M1058L and S1060A, within the spike protein have been associated to the FECV/FIPV virulence change. In this study, we have analysed the frequency of detection of such mutations in FIPV and FECV strains circulating in Italian cats and obtained information about their evolutionary relationships with reference isolates. A total of 40 FCoV strains, including 19 strains from effusions or tissue samples of FIP cats and 21 strains from faecal samples of non-FIP cats, were analysed. Mutation M1058L was detected in 16/18 FCoV-I and 1/1 FCoV-II strains associated with FIP, while change S1060A was presented by two FIPV strains. By phylogenetic analysis, FCoV sequences clustered according to the genotype but not according to the biotype, with FECV/FIPV strains recovered from the same animal being closely related. Further studies are needed to better define the genetic signatures associated with the FECV/FIPV virulence shift.

Current status on treatment options for feline infectious peritonitis and SARS-CoV-2 positive cats

Feline infectious peritonitis (FIP) is a viral-induced, immune-mediated disease of cats caused by virulent biotypes of feline coronaviruses (FCoV), known as the feline infectious peritonitis virus (FIPV). Historically, three major pharmacological approaches have been employed to treat FIP: (1) immunomodulators to stimulate the patient’s immune system non-specifically to reduce the clinical effects of the virus through a robust immune response, (2) immunosuppressive agents to dampen clinical signs temporarily, and (3) re-purposed human antiviral drugs, all of which have been unsuccessful to date in providing reliable efficacious treatment options for FIPV. Recently, antiviral studies investigating the broad-spectrum coronavirus protease inhibitor, GC376, and the adenosine nucleoside analogue GS-441524, have resulted in increased survival rates and clinical cure in many patients. However, prescriber access to these antiviral therapies is currently problematic as they have not yet obtained registration for veterinary use. Consequently, FIP remains challenging to treat. The purpose of this review is to provide an update on the current status of therapeutics for FIP. Additionally, due to interest in coronaviruses resulting from the current human pandemic, this review provides information on domesticated cats identified as SARS-CoV-2 positive.

Coronavirus Infection of the Central Nervous System: Animal Models in the Time of COVID-19

Naturally occurring coronaviral infections have been studied for several decades in the context of companion and production animals, and central nervous system involvement is a common finding, particularly in cats with feline infectious peritonitis (FIP). These companion and production animal coronaviruses have many similarities to recent human pandemic-associated coronaviruses such as SARS-CoV, MERS-CoV, and SARS-CoV2 (COVID-19). Neurological involvement is being increasingly recognized as an important clinical presentation in human COVID-19 patients, often associated with para-infectious processes, and potentially with direct infection within the CNS. Recent breakthroughs in the treatment of coronaviral infections in cats, including neurological FIP, have utilized antiviral drugs similar to those currently in human COVID-19 clinical trials. Differences in specific coronavirus and host factors are reflected in major variations in incidence and mechanisms of CNS coronaviral infection and pathology between species; however, broad lessons relating to treatment of coronavirus infection present within the CNS may be informative across species.

Feline infectious peritonitis (FIP) and coronavirus disease 19 (COVID-19): Are they similar?

SARS‐CoV‐2 has radically changed our lives causing hundreds of thousands of victims worldwide and influencing our lifestyle and habits. Feline infectious peritonitis (FIP) is a disease of felids caused by the feline coronaviruses (FCoV). FIP has been considered irremediably deadly until the last few years. Being one of the numerous coronaviruses that are well known in veterinary medicine, information on FCoV could be of interest and might give suggestions on pathogenic aspects of SARS‐CoV‐2 that are still unclear. The authors of this paper describe the most important aspects of FIP and COVID‐19 and the similarities and differences between these important diseases. SARS‐CoV‐2 and FCoV are taxonomically distant viruses, and recombination events with other coronaviruses have been reported for FCoV and have been suggested for SARS‐CoV‐2. SARS‐CoV‐2 and FCoV differ in terms of some pathogenic, clinical and pathological features. However, some of the pathogenic and immunopathogenic events that are well known in cats FIP seem to be present also in people with COVID‐19. Moreover, preventive measures currently recommended to prevent SARS‐CoV‐2 spreading have been shown to allow eradication of FIP in feline households. Finally, one of the most promising therapeutic compounds against FIP, GS‐441524, is the active form of Remdesivir, which is being used as one therapeutic option for COVID‐19.

Coronaviruses and gastrointestinal diseases

The effects of coronaviruses on the respiratory system are of great concern, but their effects on the digestive system receive much less attention. Coronaviruses that infect mammals have shown gastrointestinal pathogenicity and caused symptoms such as diarrhea and vomiting. Available data have shown that human coronaviruses, including the newly emerged SARS-CoV-2, mainly infect the respiratory system and cause symptoms such as cough and fever, while they may generate gastrointestinal symptoms. However, there is little about the relation between coronavirus and digestive system. This review specifically addresses the effects of mammalian and human coronaviruses, including SARS-CoV-2, on the digestive tract, helping to cope with the new virus infection-induced disease, COVID-19.

High-throughput viral microneutralization method for feline coronavirus using image cytometry

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There are no approved antiviral drugs or recommended vaccines for feline coronavirus infection.

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Plate-based image cytometry is used for high-throughput viral microneutralization assays.

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Image cytometry is faster and more sensitive than traditional plaque reduction neutralization tests.

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Cell seeding density, plate surface coating, virus concentration and incubation time, fluorescent labeling, and buffers were optimized.

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Cross-neutralization between FCoV type I and II viruses was not observed.

Feline coronaviruses (FCoV) are members of the alphacoronavirus genus that are further characterized by serotype (types I and II) based on the antigenicity of the spike (S) protein and by pathotype based on the associated clinical conditions. Feline enteric coronaviruses (FECV) are associated with the vast majority of infections and are typically asymptomatic. Within individual animals, FECV can mutate and cause a severe and usually fatal disease called feline infectious peritonitis (FIP), the leading infectious cause of death in domestic cat populations. There are no approved antiviral drugs or recommended vaccines to treat or prevent FCoV infection. The plaque reduction neutralization test (PRNT) traditionally employed to assess immune responses and to screen therapeutic and vaccine candidates is time-consuming, low-throughput, and typically requires 2–3 days for the formation and manual counting of cytolytic plaques. Host cells are capable of carrying heavy viral burden in the absence of visible cytolytic effects, thereby reducing the sensitivity of the assay. In addition, operator-to-operator variation can generate uncertainty in the results and digital records are not automatically created. To address these challenges we developed a novel high-throughput viral microneutralization assay, with quantification of virus-infected cells performed in a plate-based image cytometer. Host cell seeding density, microplate surface coating, virus concentration and incubation time, wash buffer and fluorescent labeling were optimized. Subsequently, this FCoV viral neutralization assay was used to explore immune correlates of protection using plasma from naturally FECV-infected cats. We demonstrate that the high-throughput viral neutralization assay using the Celigo Image Cytometer provides a robust and efficient method for the rapid screening of therapeutic antibodies, antiviral compounds, and vaccines. This method can be applied to various viral infectious diseases to accelerate vaccine and antiviral drug discovery and development.

Prevalence of Feline Coronavirus Shedding in German Catteries and Associated Risk Factors

The aim of this prospective study was to determine prevalence and potential risk factors of feline coronavirus (FCoV) shedding. Four consecutive fecal samples of 179 cats from 37 German breeding catteries were analyzed for FCoV ribonucleic acid (RNA) by real-time reverse transcriptase polymerase chain reaction (RT-qPCR). Prevalence of shedding was calculated using different numbers of fecal samples per cat (1–4) and different sampling intervals (5–28 days). Information on potential risk factors for FCoV shedding was obtained by a questionnaire. Risk factor analysis was performed using a generalized linear mixed model (GLMM). Most cats (137/179, 76.5%, 95% confidence interval (CI) 69.8–82.2) shed FCoV at least at once. None of the tested 37 catteries was free of FCoV. Prevalence calculated including all four (76.5%, 95% CI 69.8–82.2) or the last three (73.7%, 95% CI 66.8–79.7) samples per cat was significantly higher than the prevalence calculated with only the last sample (61.5%, 95% CI 54.2–68.3; p = 0.0029 and 0.0175, respectively). Young age was significantly associated with FCoV shedding while the other factors were not. For identification of FCoV shedders in multi-cat households, at least three fecal samples per cat should be analyzed. Young age is the most important risk factor for FCoV shedding.

FCoV Viral Sequences of Systemically Infected Healthy Cats Lack Gene Mutations Previously Linked to the Development of FIP

Feline infectious peritonitis (FIP)-the deadliest infectious disease of young cats in shelters or catteries-is induced by highly virulent feline coronaviruses (FCoVs) emerging in infected hosts after mutations of less virulent FCoVs. Previous studies have shown that some mutations in the open reading frames (ORF) 3c and 7b and the spike (S) gene have implications for the development of FIP, but mainly indirectly, likely also due to their association with systemic spread. The aim of the present study was to determine whether FCoV detected in organs of experimentally FCoV infected healthy cats carry some of these mutations. Viral RNA isolated from different tissues of seven asymptomatic cats infected with the field strains FCoV Zu1 or FCoV Zu3 was sequenced. Deletions in the 3c gene and mutations in the 7b and S genes that have been shown to have implications for the development of FIP were not detected, suggesting that these are not essential for systemic viral dissemination. However, deletions and single nucleotide polymorphisms leading to truncations were detected in all nonstructural proteins. These were found across all analyzed ORFs, but with significantly higher frequency in ORF 7b than ORF 3a. Additionally, a previously unknown homologous recombination site was detected in FCoV Zu1.

Complex Virome in a Mesenteric Lymph Node from a Californian Sea Lion (Zalophus Californianus) with Polyserositis and Steatitis

An emaciated subadult free-ranging California sea lion (Csl or Zalophus californianus) died following stranding with lesions similar to 11 other stranded animals characterized by chronic disseminated granulomatous inflammation with necrotizing steatitis and vasculitis, involving visceral adipose tissues in the thoracic and peritoneal cavities. Histologically, affected tissues had extensive accumulations of macrophages with perivascular lymphocytes, plasma cells, and fewer neutrophils. Using viral metagenomics on a mesenteric lymph node six mammalian viruses were identified consisting of novel parvovirus, polyomavirus, rotavirus, anellovirus, and previously described Csl adenovirus 1 and Csl bocavirus 4. The causal or contributory role of these viruses to the gross and histologic lesions of this sea lion remains to be determined.

Advantages of the Parent Nucleoside GS-441524 over Remdesivir for Covid-19 Treatment

While remdesivir has garnered much hope for its moderate anti-Covid-19 effects, its parent nucleoside, GS-441524, has been overlooked. Pharmacokinetic analysis of remdesivir evidences premature serum hydrolysis to GS-441524; GS-441524 is the predominant metabolite reaching the lungs. With its synthetic simplicity and in vivo efficacy in the veterinary setting, we contend that GS-441524 is superior to remdesivir for Covid-19 treatment.

Feline Infectious Peritonitis: Update on Pathogenesis, Diagnostics, and Treatment

Feline infectious peritonitis (FIP) is a mysterious and lethal disease of cats. The causative agent, feline coronavirus (FCoV), is ubiquitous in most feline populations, yet the disease is sporadic in nature. Mutations in the infecting virus combined with an inappropriate immune response to the FCoV contribute to the development of FIP. Diagnosis can be challenging because signs may be vague, clinical pathology parameters are nonspecific, and the gold standard for diagnosis is invasive: histopathology of affected tissue. This article discusses the developments in the understanding of this disease as well as the progress in diagnosis and treatment.

Pharmacokinetic Profile of Oral Administration of Mefloquine to Clinically Normal Cats: A Preliminary In-Vivo Study of a Potential Treatment for Feline Infectious Peritonitis (FIP)

Simple Summary

In searching for antiviral agents against feline coronaviruses and feline caliciviruses, mefloquine, a human anti-malarial drug, has been demonstrated to reduce viral load of feline coronaviruses and feline calicivirus in infected cells. In this study, mefloquine was administered orally to seven clinically healthy cats twice weekly for four doses and mefloquine concentrations in blood were measured to investigate the pharmacokinetic profile—the movement of drug in the body. The maximum blood concentration of mefloquine was 2.71 ug/mL and was reached 15 h after a single oral dose was administered. Mefloquine side effects included vomiting following administration without food in some cats, and mild increases in symmetric dimethylarginine (SDMA), an early kidney biomarker. This study provides valuable information on mefloquine’s profile in cats as an introductory step towards investigating it as a potential treatment for feline coronavirus and feline calicivirus infection in cats.

Abstract

The pharmacokinetic profile of mefloquine was investigated as a preliminary study towards a potential treatment for feline coronavirus infections (such as feline infectious peritonitis) or feline calicivirus infections. Mefloquine was administered at 62.5 mg orally to seven clinically healthy cats twice weekly for four doses and mefloquine plasma concentrations over 336 h were measured using high pressure liquid chromatography (HPLC). The peak plasma concentration (Cmax) after a single oral dose of mefloquine was 2.71 ug/mL and time to reach Cmax (Tmax) was 15 h. The elimination half-life was 224 h. The plasma concentration reached a higher level at 4.06 ug/mL when mefloquine was administered with food. Adverse effects of dosing included vomiting following administration without food in some cats. Mild increases in serum symmetric dimethylarginine (SDMA), but not creatinine, concentrations were observed. Mefloquine may provide a safe effective treatment for feline coronavirus and feline calicivirus infections in cats.

Novel human coronavirus (SARS-CoV-2): A lesson from animal coronaviruses

The recent pandemic caused by the novel human coronavirus, referrred to as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), not only is having a great impact on the health care systems and economies in all continents but it is also causing radical changes of common habits and life styles. The novel coronavirus (CoV) recognises, with high probability, a zoonotic origin but the role of animals in the SARS-CoV-2 epidemiology is still largely unknown. However, CoVs have been known in animals since several decades, so that veterinary coronavirologists have a great expertise on how to face CoV infections in animals, which could represent a model for SARS-CoV-2 infection in humans. In the present paper, we provide an up-to-date review of the literature currently available on animal CoVs, focusing on the molecular mechanisms that are responsible for the emergence of novel CoV strains with different antigenic, biologic and/or pathogenetic features. A full comprehension of the mechanisms driving the evolution of animal CoVs will help better understand the emergence, spreading, and evolution of SARS-CoV-2.

In vitro hepatic metabolism of mefloquine using microsomes from cats, dogs and the common brush-tailed possum (Trichosurus vulpecula)

Feline infectious peritonitis (FIP) is a systemic, fatal, viral-induced, immune-mediated disease of cats caused by feline infectious peritonitis virus (FIPV). Mefloquine, a human anti-malarial agent, has been shown to inhibit FIPV in vitro. As a first step to evaluate its efficacy and safety profile as a potential FIP treatment for cats, mefloquine underwent incubation in feline, canine and common brush-tailed possum microsomes and phase I metabolism cofactors to determine its rate of phase I depletion. Tramadol was used as a phase I positive control as it undergoes this reaction in both dogs and cats. Using the substrate depletion method, the in vitro intrinsic clearance (mean ± S.D.) of mefloquine by pooled feline and common brush-tailed possum microsomes was 4.5 ± 0.35 and 18.25 ± 3.18 μL/min/mg protein, respectively. However, phase I intrinsic clearance was too slow to determine with canine microsomes. Liquid chromatography-mass spectrometry (LC-MS) identified carboxymefloquine in samples generated by feline microsomes as well as negative controls, suggesting some mefloquine instability. Mefloquine also underwent incubation with feline, canine and common brush-tailed possum microsomes and phase II glucuronidative metabolism cofactors. O-desmethyltramadol (ODMT or M1) was used as a positive control as it undergoes a phase II glucuronidation reaction in these species. The rates of phase II mefloquine depletion by microsomes by all three species were too slow to estimate. Therefore mefloquine likely undergoes phase I hepatic metabolism catalysed by feline and common brush-tailed possum microsomes but not phase II glucuronidative metabolism in all three species and mefloquine is not likely to have delayed elimination in cats with clinically normal, hepatic function.

Origin and transmission of Feline coronavirus type I in domestic cats from Northern Italy: a phylogeographic approach

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FCoV type I only was observed in cats from Northern Italy.

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A high genetic variability of the Italian FCoV circulating strains was observed.

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Different strains of FCoV cocirculate in Northern Italy.

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FCoV likely originated in USA in the 1950s-1970s and thereafter spread to Europe.

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In the last decade FCoV segregates mainly on the basis of geographic origin.

Feline coronavirus (FCoV) is responsible, along with an inadequate immune response of the host, for Feline infectious peritonitis (FIP), one of the most frequent and deadly infectious feline disease worldwide. This study analyzed the genetic characteristics of the spike (S) gene of 33 FCoVs circulating in Northern Italy between 2011 and 2015 in cats with or without FIP. In order to reconstruct the most probable places of origin and dispersion of FCoV among Italian cats, a phylogeographic approach was performed based on 106 FCoV S gene partial sequences from cats, including the 33 novel Italian sequences and 73 retrieved from public databases. Only FCoV type I was found in the Italian cats. The estimated mean evolutionary rate of FCoV was 2.4 × 10^-2 subs/site/year (95% HPD: 1.3-3.7 × 10^-2), confirming the high genetic variability in the circulating strains. All the isolates clustered in a unique highly significant clade that likely originated from USA between the 1950s and the 1970s, confirming the first descriptions of the disease in American cats. Our results suggest that from USA the virus likely entered Germany and thereafter spread to other European countries. Phylogeography showed that sequences segregated mainly by geographical origin. In the 2010s Italian sequences clustered in different subclades, confirming that different strains cocirculate in Italy. Further studies on archival samples and other genetic regions of FCoV are suggested in order to confirm the present results and to reconstruct a more in-depth detailed virus dispersion pattern for the definition of possible control measures.

Retrospective analysis of pleural effusion in cats

OBJECTIVES

Pleural effusion is a common presenting cause for feline patients in small animal practice. The objectives of this study were to identify possible correlations between the aetiology of effusion and clinical and laboratory findings.

METHODS

In this retrospective study of 306 cats diagnosed with pleural effusion of established aetiology, cats were divided into six major groups: cardiac disease (CD), feline infectious peritonitis (FIP), neoplasia, pyothorax, chylothorax and miscellaneous. Clinical, laboratory and radiographic parameters were compared between groups.

RESULTS

CD was the most common aetiology (35.3%), followed by neoplasia (30.7%), pyothorax (8.8%), FIP (8.5%), chylothorax (4.6%) and miscellaneous diseases (3.7%). In 26 (8.5%) cats, more than one underlying disease was diagnosed as a possible aetiology for pleural effusion. Cats with FIP were significantly younger than those with CD (P <0.001) and neoplasia (P <0.001). Cats with CD were presented with a significantly lower body temperature compared with cats with FIP (P = 0.022). Cats with CD had significantly higher serum alanine aminotransferase activity compared with all other cats (FIP and pyothorax, P <0.001; neoplasia and chylothorax, P = 0.02) and serum alkaline phosphatase activity compared with the pyothorax (P <0.001) and FIP groups (P = 0.04), and significantly lower protein concentrations (FIP, pyothorax and neoplasia, P <0.001; chylothorax, P = 0.04) and nucleated cell counts in the effusion than all other groups (pyothorax and neoplasia, P <0.001; chylothorax, P = 0.02; FIP, P = 0.04). The glucose level in the effusion of cats with pyothorax was significantly lower than glucose levels in patients with CD, neoplasia and chylothorax (P <0.001). Of 249 cats with a follow-up of at least 10 days, 55.8% died or were euthanased during that time.

CONCLUSIONS AND RELEVANCE

CD and neoplasia were the most common causes for feline pleural effusion. Age, liver enzymes, as well as cell count, protein and glucose levels in the effusion can aid in the investigation of underlying aetiologies.

Diagnosis of Feline Infectious Peritonitis: A Review of the Current Literature

Feline infectious peritonitis (FIP) is a fatal disease that poses several challenges for veterinarians: clinical signs and laboratory changes are non-specific, and there are two pathotypes of the etiologic agent feline coronavirus (FCoV), sometimes referred to as feline enteric coronavirus (FECV) and feline infectious peritonitis virus (FIPV) that vary fundamentally in their virulence, but are indistinguishable by a number of diagnostic methods. This review focuses on all important steps every veterinary practitioner has to deal with and new diagnostic tests that can be considered when encountering a cat with suspected FIP with the aim to establish a definitive diagnosis. It gives an overview on all available direct and indirect diagnostic tests and their sensitivity and specificity reported in the literature in different sample material. By providing summarized data for sensitivity and specificity of each diagnostic test and each sample material, which can easily be accessed in tables, this review can help to facilitate the interpretation of different diagnostic tests and raise awareness of their advantages and limitations. Additionally, diagnostic trees depict recommended diagnostic steps that should be performed in cats suspected of having FIP based on their clinical signs or clinicopathologic abnormalities. These steps can easily be followed in clinical practice.

Pan-European Study on the Prevalence of the Feline Leukaemia Virus Infection - Reported by the European Advisory Board on Cat Diseases (ABCD Europe)

Feline leukaemia virus (FeLV) is a retrovirus associated with fatal disease in progressively infected cats. While testing/removal and vaccination led to a decreased prevalence of FeLV, recently, this decrease has reportedly stagnated in some countries. This study aimed to prospectively determine the prevalence of FeLV viraemia in cats taken to veterinary facilities in 32 European countries. FeLV viral RNA was semiquantitatively detected in saliva, using RT-qPCR as a measure of viraemia. Risk and protective factors were assessed using an online questionnaire to report geographic, demographic, husbandry, FeLV vaccination, and clinical data. The overall prevalence of FeLV viraemia in cats visiting a veterinary facility, of which 10.4% were shelter and rescue cats, was 2.3% (141/6005; 95% CI: 2.0%–2.8%) with the highest prevalences in Portugal, Hungary, and Italy/Malta (5.7%–8.8%). Using multivariate analysis, seven risk factors (Southern Europe, male intact, 1–6 years of age, indoor and outdoor or outdoor-only living, living in a group of ≥5 cats, illness), and three protective factors (Northern Europe, Western Europe, pedigree cats) were identified. Using classification and regression tree (CART) analysis, the origin of cats in Europe, pedigree, and access to outdoors were important predictors of FeLV status. FeLV-infected sick cats shed more viral RNA than FeLV-infected healthy cats, and they suffered more frequently from anaemia, anorexia, and gingivitis/stomatitis than uninfected sick cats. Most cats had never been FeLV-vaccinated; vaccination rates were indirectly associated with the gross domestic product (GDP) per capita. In conclusion, we identified countries where FeLV was undetectable, demonstrating that the infection can be eradicated and highlighting those regions where awareness and prevention should be increased.

Diagnosis of non-effusive feline infectious peritonitis by reverse transcriptase quantitative PCR from mesenteric lymph node fine-needle aspirates

OBJECTIVES

The aim of this study was to evaluate a feline coronavirus (FCoV) reverse transcriptase quantitative PCR (RT-qPCR) on fine-needle aspirates (FNAs) from mesenteric lymph nodes (MLNs) collected in sterile saline for the purpose of diagnosing non-effusive feline infectious peritonitis (FIP) in cats.

METHODS

First, the ability of the assay to detect viral RNA in MLN FNA preparations compared with MLN biopsy preparations was assessed in matched samples from eight cats. Second, a panel of MLN FNA samples was collected from a series of cats representing non-effusive FIP cases (n = 20), FCoV-seropositive individuals (n = 8) and FCoV-seronegative individuals (n = 18). Disease status of the animals was determined using a combination of gross pathology, histopathology and/or 'FIP profile', consisting of serology, clinical pathology and clinical signs.

RESULTS

Viral RNA was detected in 18/20 non-effusive FIP cases; it was not detected in two cases that presented with neurological FIP. Samples from 18 seronegative non-FIP control cats and 7/8 samples from seropositive non-FIP control cats contained no detectable viral RNA. Thus, as a method for diagnosing non-effusive FIP, MLN FNA RT-qPCR had an overall sensitivity of 90.0% and specificity of 96.1%.

CONCLUSIONS AND RELEVANCE

In cases with a high index of suspicion of disease, RT-qPCR targeting FCoV in MLN FNA can provide important information to support the ante-mortem diagnosis of non-effusive FIP. Importantly, viral RNA can be reliably detected in MLN FNA samples in saline submitted via the national mail service. When applied in combination with biochemistry, haematology and serological tests in cases with a high index of suspicion of disease, the results of this assay may be used to support a diagnosis of non-effusive FIP.

Mucosal Immune Response to Feline Enteric Coronavirus Infection

Feline infectious peritonitis is a devastating, fatal disease of domestic cats caused by a pathogenic mutant virus derived from the ubiquitous feline enteric coronavirus (FECV). Infection by FECV is generally subclinical, and little is known about the mucosal immune response that controls and eliminates the virus. We investigated the mucosal immune response against FECV in an endemically infected breeding colony over a seven-month period. Thirty-three cats were grouped according to FECV seropositivity and fecal virus shedding into naïve/immunologically quiescent, convalescent and actively infected groups. Blood, fecal samples and colon biopsies were collected to assess the mucosal and systemic immunologic and virologic profile. Results showed that cats with active FECV infections have strong systemic IgG and mucosal IgA responses that wane after virus clearance. Significant FECV-specific mucosal T cell IFNγ responses were not detected in any of the three groups. A shift toward an inflammatory state in the mucosa was suggested by increased IL17:FoxP3 expression. However, no histologic abnormalities were observed, and no shifts in lymphocyte subpopulation phenotype or proliferation were noted. Together, the results suggest that control of FECV is mediated by humoral mucosal and systemic responses and that perturbations in the primary reservoir organ (colon) are minimal.

Serological Screening for Coronavirus Infections in Cats

Coronaviruses (CoVs) are widespread among mammals and birds and known for their potential for cross-species transmission. In cats, infections with feline coronaviruses (FCoVs) are common. Several non-feline coronaviruses have been reported to infect feline cells as well as cats after experimental infection, supported by their ability to engage the feline receptor ortholog for cell entry. However, whether cats might become naturally infected with CoVs of other species is unknown. We analyzed coronavirus infections in cats by serological monitoring. In total 137 cat serum samples and 25 FCoV type 1 or type 2-specific antisera were screened for the presence of antibodies against the S1 receptor binding subunit of the CoV spike protein, which is immunogenic and possesses low amino acid sequence identity among coronavirus species. Seventy-eight sera were positive for antibodies that recognized one or more coronavirus S1s whereas 1 serum exclusively reacted with human coronavirus 229E (HCoV-229E) and two sera exclusively reacted with porcine delta coronavirus (PDCoV). We observed antigenic cross-reactivity between S1s of type 1 and type 2 FCoVs, and between FCoV type 1 and porcine epidemic diarrhea virus (PEDV). Domain mapping of antibody epitopes indicated the presence of conserved epitope(s) particularly in the CD domains of S1. The cross-reactivity of FCoV type 1 and PEDV was also observed at the level of virus neutralization. To conclude, we provide the first evidence of antigenic cross-reactivity among S1 proteins of coronaviruses, which should be considered in the development of serological diagnoses. In addition, the potential role of cats in cross-species transmission of coronaviruses cannot be excluded.

Feline infectious peritonitis: answers to frequently asked questions concerning FIP and coronavirus

Feline infectious peritonitis (FIP) is caused by infection with feline coronavirus (FCoV), a highly infectious virus transmitted mostly indirectly, by sharing litter trays with a FCoV excretor, or by fomites. The majority of FCoV-infected cats remain healthy, with up to 12% developing FIP. While any age or breed of cat can develop FIP, FIP disproportionately affects pedigree kittens: most studies found that around 70% of FIP cases occurred in pure-bred cats under 2 years of age. In this paper, some questions about FCoV and FIP that are likely to be asked of, and by, a veterinary nurse will be addressed.

Pathogenesis of oral type I feline infectious peritonitis virus (FIPV) infection: Antibody-dependent enhancement infection of cats with type I FIPV via the oral route

Feline infectious peritonitis virus (FIPV) causes a severe, immune-mediated disease called FIP in domestic and wild cats. It is unclear whether FIP transmits from cat to cat through the oral route of FIPV infection, and the reason for this includes that FIP is caused by oral inoculation with some FIPV strains (e.g., type II FIPV WSU 79-1146), but is not caused by other FIPV (e.g., type I FIPV KU-2 strain: FIPV-I KU-2). In this study, when cats passively immunized with anti-FIPV-I KU-2 antibodies were orally inoculated with FIPV-I KU-2, FIP was caused at a 50% probability, i.e., FIPV not causing FIP through oral infection caused FIP by inducing antibody-dependent enhancement. Many strains of type I FIPV do not cause FIP by inoculation through the oral route in cats. Based on the findings of this study, type I FIPV which orally infected cats may cause FIP depending on the condition.

Differential recognition of peptides within feline coronavirus polyprotein 1 ab by sera from healthy cats and cats with feline infectious peritonitis

The aim of the study was to identify peptides within the polyprotein (Pp) 1 ab that are differentially recognised by cats with either enteric or systemic disease following infection with feline coronavirus. Overlapping 12-mer peptides (n = 28,426) across the entire Pp1ab were arrayed on peptide chips and reacted with pooled sera from coronavirus seropositive cats and from one seronegative cat. Eleven peptides were further tested in ELISA with individual serum samples, and three were selected for further screening. Two peptides (16433 and 4934) in the nsp3 region encoding the papain 1 and 2 proteases were identified for final testing. Peptide 4934 reacted equally with positive sera from healthy cats and cats with feline infectious peritonitis (FIP), while peptide 16433 was recognized predominantly by FIP-affected cats. The value of antibody tests based on these peptides in differentiating between the enteric and FIP forms of feline coronavirus infection remains to be determined.

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Cats develop antibodies to polyprotein 1 ab (Pp1ab) of feline coronavirus.

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This is most evident for cats with feline infectious peritonitis (FIP).

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Differences exist in responses to selected peptides between FIP and non-FIP cats.

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Such differences may be utilised for development of a serological test for FIP.

Detection of feline coronavirus mutations in paraffin-embedded tissues in cats with feline infectious peritonitis and controls

OBJECTIVES

The amino acid substitutions M1058L and S1060A in the spike protein of feline coronavirus (FCoV) have been postulated to be responsible for the development of the pathogenic feline infectious peritonitis virus (FIPV), which causes feline infectious peritonitis (FIP). The aim of the following study was to investigate the presence of mutated virus in tissue samples of cats with and without FIP.

METHODS

The study population consisted of 64 cats, 34 of which were diagnosed with FIP and 30 control cats. All cases underwent autopsy, histopathology and immunohistochemistry (IHC) for FCoV. Furthermore, a genotype-discriminating quantitative reverse transcriptase PCR (RT-qPCR) was performed on shavings of paraffin-embedded tissues to discriminate between cats with FIP and controls, and the sensitivity and specificity of this discriminating RT-qPCR were calculated using 95% confidence intervals (CIs).

RESULTS

Specificity of genotype-discriminating RT-qPCR was 100.0% (95% CI 88.4-100.0), and sensitivity was 70.6% (95% CI 52.5-84.9). In cats with FIP, 24/34 tested positive for FIPV. In samples of three control cats and in seven cats with FIP, FCoV was found, but genotyping was not possible owing to low FCoV RNA concentrations. Out of the positive samples, 23 showed the amino acid substitution M1058L in the spike protein and none the substitution S1060A. One sample in a cat with FIP revealed a mixed population of non-mutated FCoV and FIPV (mixed genotype). For one sample genotyping was not possible despite high viral load, and two samples were negative for FCoV.

CONCLUSIONS AND RELEVANCE

As none of the control animals showed FCoV amino acid substitutions previously demonstrated in cats with FIP, it can be presumed that the substitution M1058L correlates with the presence of FIP. FCoV was detected in low concentration in tissues of control animals, confirming the ability of FCoV to spread systemically. The fact that no negative controls were included in the IHC protocol could potentially lead to an underestimation of the sensitivity of the RT-qPCR.

Immunocytochemistry of mesenteric lymph node fine-needle aspirates in the diagnosis of feline infectious peritonitis

Immunohistochemistry (IHC) of tissue samples is considered the gold standard for diagnosing feline infectious peritonitis (FIP), and, in cats without body cavity effusion, IHC is the only method available to establish definitive antemortem diagnosis. However, IHC requires invasive tissue sample collection. We evaluated sensitivity and specificity of an immunocytochemical assay of fine-needle aspirates (FNAs) of mesenteric lymph nodes that can be obtained noninvasively by ultrasound-guided aspiration to diagnose FIP. FNAs of mesenteric lymph nodes were obtained postmortem from 41 cats suspected of having FIP based on clinical and/or laboratory findings. FIP was confirmed immunohistochemically in 30 cats. In the other 11 cats, a disease other than FIP, which explained the clinical signs, was diagnosed histopathologically. Immunocytochemistry (ICC) was performed as an avidin-biotin complex method using a monoclonal anti-FCoV IgG 2A. Sensitivity, specificity, negative and positive predictive values (NPV, PPV, respectively) including 95% confidence intervals (95% CIs) were determined. ICC was positive in 17 of 30 cats with FIP, but also in 1 of 11 control cats that was diagnosed with lymphoma. Sensitivity of ICC was 53% (95% CI: 34-72); specificity 91% (95% CI: 59-100); NPV 42% (95% CI: 22-63); and PPV 94% (95% CI: 71-100). In a lethal disease such as FIP, specificity is most important in order to avoid euthanasia of unaffected cats. Given that a false-positive result occurred and FIP was correctly detected in only approximately half of the cases of FIP, ICC of mesenteric lymph node FNA alone cannot reliably confirm or exclude FIP, but can be a helpful test in conjunction with other diagnostic measures.

Circulation and genetic diversity of Feline coronavirus type I and II from clinically healthy and FIP-suspected cats in China

Feline infectious peritonitis (FIP) is a fatal infectious disease of wild and domestic cats, and the occurrence of FIP is frequently reported in China. To trace the evolution of type I and II feline coronavirus in China, 115 samples of ascetic fluid from FIP-suspected cats and 54 fecal samples from clinically healthy cats were collected from veterinary hospitals in China. The presence of FCoV in the samples was detected by RT-PCR targeting the 6b gene. The results revealed that a total of 126 (74.6%, 126/169) samples were positive for FCoV: 75.7% (87/115) of the FIP-suspected samples were positive for FCoV, and 72.2% (39/54) of the clinically healthy samples were positive for FCoV. Of the 126 FCoV-positive samples, 95 partial S genes were successfully sequenced. The partial S gene-based genotyping indicated that type I FCoV and type II FCoV accounted for 95.8% (91/95) and 4.2% (4/95), respectively. The partial S gene-based phylogenetic analyses showed that the 91 type I FCoV strains exhibited genetic diversity; the four type II FCoV strains exhibited a close relationship with type II FCoV strains from Taiwan. Three type I FCoV strains, HLJ/HRB/2016/10, HLJ/HRB/2016/11 and HLJ/HRB/2016/13, formed one potential new clade in the nearly complete genome-based phylogenetic trees. Further analysis revealed that FCoV infection appeared to be significantly correlated with a multi-cat environment (p < 0.01) and with age (p < 0.01). The S gene of the three type I FCoV strains identified in China, BJ/2017/27, BJ/2018/22 and XM/2018/04, exhibited a six nucleotide deletion (C⁴⁰³⁵ AGCTC⁴⁰⁴⁰ ). Our data provide evidence that type I and type II FCoV strains co-circulate in the FIP-affected cats in China. Type I FCoV strains exhibited high prevalence and genetic diversity in both FIP-affected cats and clinically healthy cats, and a multi-cat environment and age (<6 months) were significantly associated with FCoV infection.

Immunohistochemical studies on meningoencephalitis in feline infectious peritonitis (FIP)

The present study describes the association between inflammatory cell types and feline infectious peritonitis virus (FIPV) antigen in the brain of 4 cats diagnosed as feline infectious peritonitis (FIP). Immunohistochemically, FIPV antigens were detected in the inflammatory foci of the leptomeninges, choroid plexus and ventricles in 3 of the 4 cats. In 3 cases, inflammatory foci mainly consisted of CD204- and Iba1-positive macrophages, and the FIPV antigens were found in the macrophages. In the other case which was negative for FIPV antigen, severe inflammation predominantly consisting of CD20-positive B lymphocytes was observed in the leptomeninges and subventricles, accompanied with diffuse proliferation of gemistocytic astrocytes. The difference in histopathology may reflect the inflammatory process or the strain variation of FIP virus.

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

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Differences in the S protein modulate serotype II FCoV infection of macrophages.

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Critical residues in the spike S2 domain of type II FCoV affecting cell tropism.

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Cooperativity at 5 positions in the S protein modulates FCoV macrophage entry.

The ability to infect and replicate in monocytes/macrophages is a critically distinguishing feature between the two feline coronavirus (FCoV) pathotypes: feline enteric coronavirus (FECV; low-virulent) and feline infectious peritonitis virus (FIPV; lethal). Previously, by comparing serotype II strains FIPV 79-1146 and FECV 79-1683 and recombinant chimeric forms thereof in cultured feline bone marrow macrophages, we mapped this difference to the C-terminal part of the viral spike (S) protein (S2). In view of the later identified diagnostic difference in this very part of the S protein of serotype I FCoV pathotypes, the present study aimed to further define the contribution of the earlier observed ten amino acids difference to the serotype II virus phenotype in macrophages. Using targeted RNA recombination as a reverse genetics system we introduced the mutations singly and in combinations into the S gene and evaluated their effects on the infection characteristics of the mutant viruses in macrophages. While some of the single mutations had a significant effect, none of them fully reverted the infection phenotype. Only by combining five specific mutations the infections mediated by the FIPV and FECV spike proteins could be fully blocked or potentiated, respectively. Hence, the differential macrophage infection phenotype is caused by the cooperative effect of five mutations, which occur in five functionally different domains of the spike fusion subunit S2. The significance of these observations will be discussed, taking into account also some questions related to the identity of the virus strains used.

Behavioral awareness in the feline consultation: Understanding physical and emotional health

Practical relevance: Awareness of the strong connection between observed behavior and physical and emotional health is essential for patient welfare. It is often a change in the individual's normal behavior that informs owners and veterinarians of the possibility of illness, pain and stress/distress. There is ample evidence in the feline literature that medical and behavioral health go hand in hand. In most feline cases, medical and behavioral conditions contribute concurrently to clinical signs. Clinical challenges: Our domestic cats do not express change in physiological and emotional states in a way that is easily recognized. Therefore, it can be difficult to diagnose medical and behavioral illnesses and ascertain contributions from each one to the final diagnosis. When various levels of stress are present, especially distress, this compromises behavioral and physical health, and influences treatment outcomes.

AIMS

This review is intended to help veterinarians recognize physical and behavioral changes associated with acute stress through to chronic distress, including stress-associated diseases. An emphasis on thorough history-taking will allow the clinician to ascertain which signs are behavioral and which are medical, with the understanding that they are not mutually exclusive. Equally important is the contribution of pain, chronic disease and poor environmental situations to behavioral changes and the expression of medical disorders. Evidence base: There is an increasing amount of evidence that stress and distress have profound effects on feline health, behavior and welfare. The authors have drawn on a substantial body of published veterinary research in producing this review.

Prevalence of enteropathogens in cats with and without diarrhea in four different management models for unowned cats in the southeast United States

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Most cats in shelters, sanctuaries, foster homes, and trap-neuter-return programs carried at least one enteropathogen.

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Tritrichomonas foetus and coronavirus were more common in cats with diarrhea.

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Other bacterial, viral, protozoal, and helminth enteropathogens were present in cats with normal feces and diarrhea.

The objective of this study was to determine the prevalence of enteropathogens in cats with and without diarrhea in four different models for managing unowned cats: short-term animal shelter, long-term sanctuary, home-based foster care, and trap-neuter-return. Fecal samples from 482 cats, approximately half of the cats with normal fecal consistency and half with diarrhea, were tested by zinc sulfate centrifugation and by real-time PCR for a panel of enteropathogens.

At least one enteropathogen of feline or zoonotic importance was detected in a majority of cats, regardless of management model. For most enteropathogens, the presence or absence of diarrhea was not significantly associated with infection, the exceptions being Tritrichomonas foetus in sanctuary cats with diarrhea (26%) and normal fecal consistency (10%), respectively (P ≤ 0.04), and feline coronavirus in foster cats (80% and 58%) (P ≤ 0.001). The types of enteropathogens detected were related to the type of management model, e.g., viral and protozoal infections were most common in shelters, sanctuaries, and foster homes (confinement systems), whereas helminth infections were most common in trap-neuter-return programs (free-roaming cats).

These results suggest that management practices for unowned cats are inadequate for control of enteropathogens and that the presence of diarrhea is a poor indicator of enteropathogen carriage. Risk-management strategies to reduce transmission to people and other animals should focus on sanitation, housing, compliance with preventive care guidelines, periodic surveillance, response to specific enteropathogens, humane population management of free-roaming community cats, public health education, and minimizing the duration and number of cats in mass confinement.

Diagnosis of feline infectious peritonitis: Update on evidence supporting available tests

Practical relevance: Feline coronavirus (FCoV) infection is very common in cats, usually causing only mild intestinal signs such as diarrhoea. Up to 10% of FCoV infections, however, result in the fatal disease feline infectious peritonitis (FIP). Clinical challenges: Obtaining a definitive diagnosis of FIP based on non-invasive approaches is difficult. Confirmation of the disease relies on finding appropriate cytological or histopathological changes in association with positive immunostaining for FCoV antigen. In FIP cases with effusions, cytology and immunostaining on effusion samples can be relatively easy to perform; otherwise obtaining diagnostic samples is more challenging and collection of biopsies from tissues with gross lesions is necessary. In the absence of a definitive diagnosis, a high index of suspicion of FIP may be obtained from the cat's signalment and history, combined with findings on clinical examination and laboratory test results. If largely consistent with FIP, these can be used as a basis for discussion with the owner about whether additional, more invasive, diagnostic tests are warranted. In some cases it may be that euthanasia is discussed as an alternative to pursuing a definitive diagnosis ante-mortem, especially if financial limitations exist or where there are concerns over a cat's ability to tolerate invasive diagnostic procedures. Ideally, the diagnosis should be confirmed in such patients from samples taken at post-mortem examination. Global importance: FIP occurs wherever FCoV infection is present in cats, which equates to most parts of the world. Evidence base: This review provides a comprehensive overview of how to approach the diagnosis of FIP, focusing on the tests available to the veterinary practitioner and recently published evidence supporting their use.

A retrospective study of the neuropathology and diagnosis of naturally occurring feline infectious peritonitis

Feline infectious peritonitis (FIP) is one of the most important viral diseases of cats worldwide. Our study describes the neuropathology and the diagnostic features of 26 cases of FIP in domestic cats. The average age of affected individuals was 11.8 mo, and there was no sex or breed predisposition. Clinical neurologic signs were noted in 22 cases, and rabies was clinically suspected in 11 cases. Twenty cats had lesions in multiple organs, and 6 cats had lesions only in the brain. Gross neuropathologic changes occurred in 15 cases and consisted of hydrocephalus (10 cases), cerebellar herniation through the foramen magnum (6 cases), cerebral swelling with flattening of gyri (2 cases), and accumulation of fibrin within ventricles (2 cases) or leptomeninges (1 case). Histologically, 3 main distinct distributions of neuropathologic changes were observed, namely periventricular encephalitis (12 cases), rhombencephalitis (8 cases), and diffuse leptomeningitis with superficial encephalitis (6 cases). Fresh tissue samples were submitted for fluorescent antibody testing (FAT) after autopsy in 17 cases, and positive results were found in only 7 cases. Immunohistochemistry (IHC) for feline coronavirus confirmed the diagnosis in all 26 cases. IHC appears to be a more sensitive and reliable test for confirmation of FIP than is FAT.

Feline coronavirus antibody titer in cerebrospinal fluid from cats with neurological signs

To investigate the utility of cerebrospinal fluid (CSF) anti-feline coronavirus (FCoV) antibody test for diagnosis of feline infectious peritonitis (FIP), the antibody titers were tested in CSF and sera from 271 FIP-suspected neurological cats. CSF antibody was detected in 28 cats, which were divided into 2 groups; 15 with CSF titer of 1:80 or lower and 13 with CSF titer of 1:640 or higher. In the latter group, reciprocal serum titer/reciprocal CSF titer was 8 or lower, which is extremely lower than normal range (256-2048), and FCoV RNA was detected in all of 11 CSF samples assayed by RT-PCR. Our findings indicate that CSF titer of 1:640 or higher may be served as a candidate for the index for diagnosing FIP.

Skin as a marker of general feline health: Cutaneous manifestations of infectious disease

Practical relevance: Infectious disease in feline patients often presents a diagnostic challenge. This article reviews the most relevant viral, bacterial and protozoal diseases and their cutaneous manifestations. Many of the diseases discussed have overlapping presentations or may mimic more common noninfectious disease processes. The purpose of the article is to reinforce knowledge of common and uncommon infectious diseases, help practitioners identify possible infectious dermatoses, create a comprehensive and prioritized differential list, and provide guidance for the diagnosis of these diseases. A working knowledge of these clinical syndromes is important if what is thought to be a case of a common disease does not respond to conventional management.

AUDIENCE

This review is aimed at veterinarians who treat cats and especially those with an interest in feline dermatology. Tables are included to allow the reader to formulate a concise list of differential diagnoses for clinically similar presentations. The diagnostic approach to a case of ulcerative facial dermatitis is reviewed in a Case Notes quiz. Evidence base: This article includes up-to-date information regarding dermatologic manifestations of less commonly encountered feline cutaneous infectious diseases. Information has been drawn from the published, peer-reviewed literature and the most recent textbook chapters with a particular aim of describing and differentiating clinical lesions and the diagnostic approach to cutaneous disease, especially in unusual cases.

Discrepancies between feline coronavirus antibody and nucleic acid detection in effusions of cats with suspected feline infectious peritonitis

Intra-vitam diagnosis of feline infectious peritonitis (FIP) is a challenge for veterinary diagnosticians, since there are no highly specific and sensitive assays currently available. With the aim to contribute to fill this diagnostic gap, a total of 61 effusions from cats with suspected effusive FIP were collected intra-vitam for detection of feline coronavirus (FCoV) antibodies and RNA by means of indirect immunofluorescence (IIF) assay and real-time RT-PCR (qRT-PCR), respectively. In 5 effusions there was no evidence for either FCoV RNA or antibodies, 51 and 52 specimens tested positive by IIF and qRT-PCR, respectively, although antibody titres ≥ 1:1600, which are considered highly suggestive of FIP, were detected only in 37 effusions. Three samples with high antibody levels tested negative by qRT-PCR, whereas 18 qRT-PCR positive effusions contained no or low-titre antibodies. qRT-PCR positive samples with low antibody titres mostly contained low FCoV RNA loads, although the highest antibody titres were detected in effusions with C_T values > 30. In conclusion, combining the two methods, i.e., antibody and RNA detection would help improving the intra-vitam diagnosis of effusive FIP.

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Effusions from cats with suspected FIP were analysed for detection of feline coronavirus (FCoV) antibodies and RNA.

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Using a cut-off of 1:1600 for FCoV antibodies, only 40/61 samples were in agreement between the two tests.

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Most effusions with low FCoV loads were found to contain low specific antibody titres.

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Combining serological and molecular methods results in an increase of the diagnostic efficiency.

Interferon-omega: Current status in clinical applications

Since 1985, interferon (IFN)-ω, a type I IFN, has been identified in many animals, but not canines and mice. It has been demonstrated to have antiviral, anti-proliferation, and antitumor activities that are similar to those of IFN-α. To date, IFN-ω has been explored as a treatment option for some diseases or viral infections in humans and other animals. Studies have revealed that human IFN-ω displays antitumor activities in some models of human cancer cells and that it can be used to diagnose some diseases. While recombinant feline IFN-ω has been licensed in several countries for treating canine parvovirus, feline leukemia virus, and feline immunodeficiency virus infections, it also exhibits a certain efficacy when used to treat other viral infections or diseases. This review examines the known biological activity of IFN-ω and its clinical applications. We expect that the information provided in this review will stimulate further studies of IFN-ω as a therapeutic agent.

Nanoparticulate vacuolar ATPase blocker exhibits potent host-targeted antiviral activity against feline coronavirus

Feline infectious peritonitis (FIP), caused by a mutated feline coronavirus, is one of the most serious and fatal viral diseases in cats. The disease remains incurable, and there is no effective vaccine available. In light of the pathogenic mechanism of feline coronavirus that relies on endosomal acidification for cytoplasmic entry, a novel vacuolar ATPase blocker, diphyllin, and its nanoformulation are herein investigated for their antiviral activity against the type II feline infectious peritonitis virus (FIPV). Experimental results show that diphyllin dose-dependently inhibits endosomal acidification in fcwf-4 cells, alters the cellular susceptibility to FIPV, and inhibits the downstream virus replication. In addition, diphyllin delivered by polymeric nanoparticles consisting of poly(ethylene glycol)-block-poly(lactide-co-glycolide) (PEG-PLGA) further demonstrates an improved safety profile and enhanced inhibitory activity against FIPV. In an in vitro model of antibody-dependent enhancement of FIPV infection, diphyllin nanoparticles showed a prominent antiviral effect against the feline coronavirus. In addition, the diphyllin nanoparticles were well tolerated in mice following high-dose intravenous administration. This study highlights the therapeutic potential of diphyllin and its nanoformulation for the treatment of FIP.

Utility of an immunocytochemical assay using aqueous humor in the diagnosis of feline infectious peritonitis

Objective

In cats suffering from feline infectious peritonitis (FIP) without effusion, antemortem diagnosis is challenging. Uveitis is common in these cats. It was the aim of this study to evaluate sensitivity and specificity of an immunocytochemical assay (ICC) in aqueous humor of cats suspected of having FIP.

Animals studied

The study included 26 cats with immunohistochemically confirmed FIP and 12 control cats for which FIP was suspected due to similar clinical or laboratory changes, but which suffered from other diseases confirmed via histopathology.

Procedures

All aqueous humor samples were collected postmortem by paracentesis. ICC was carried out as avidin–biotin complex method. Sensitivity, specificity, and the overall accuracy including 95% confidence intervals (95% CI) were calculated.

Results

Immunocytochemistry was positive in 16 of 25 cats with FIP and 2 of 11 control cats (one cat with lymphoma, one with pulmonary adenocarcinoma). Aqueous humor samples of one cat with FIP and of one control cat were excluded from statistical analysis. Sensitivity was 64.0% (95% CI: 42.5–82.0); specificity 81.8% (95% CI: 48.2–97.7); and overall accuracy 69.4% (95% CI: 51.9–83.7).

Conclusions

As false‐positive results occurred and specificity is most important in the diagnosis of FIP, the diagnostic utility of ICC in aqueous humor is limited. Further studies are required to clarify the origin of false‐positive ICC results.

Feline biliary tree and gallbladder disease: Aetiology, diagnosis and treatment

Practical relevance Diseases of the biliary tree and gallbladder are more common in cats than diseases of the liver parenchyma. The parenchyma is usually affected secondarily to systemic illnesses, while the biliary system is the prime target for infectious agents (eg, bacteria and flukes) and non-infectious conditions (eg, neoplasia and cysts). Clinical approaches Cats with biliary disease are evaluated because of common feline clinical signs such as anorexia, nausea, vomiting and lethargy. Icterus may or may not be obvious. Biopsies for histological evaluation, and bile aspirates for culture and cytological evaluation are helpful diagnostically. Antibiotics and immunosuppressive drugs have been used successfully. Hepatosupportive drugs may help in liquefying thick bile and protecting hepatic tissue from damage. Ultrasound is a noninvasive diagnostic tool that may help in identifying dilated bile ducts, liver cysts and choleliths. It is also used to guide percutaneous bile aspiration. Audience This review, written for all veterinarians who treat cats, describes the various conditions that can affect the feline biliary tree and gallbladder. Treatment options are discussed, and brief summaries provided of surgical techniques and diagnostic approaches. Evidence base The veterinary literature pertaining to feline biliary disease is comprehensively reviewed. When appropriate, data on dogs and humans has been included to provide background information. Based on the available literature, more research into feline biliary diseases is needed.

Comparison of real-time reverse transcriptase polymerase chain reaction of peripheral blood mononuclear cells, serum and cell-free body cavity effusion for the diagnosis of feline infectious peritonitis

Objectives Diagnosis of feline infectious peritonitis (FIP) remains challenging, especially in cats without effusions. The objective of this study was to evaluate the sensitivity and specificity of a real-time reverse transcriptase polymerase chain reaction (RT-PCR) detecting feline coronavirus (FCoV) RNA in peripheral blood mononuclear cells (PBMCs) and serum in comparison with the same real-time RT-PCR in cell-free body cavity effusion. Methods This prospective case-control study included 92 cats. Forty-three cats had a definitive diagnosis of FIP, established either by histopathological examination (n = 28) or by positive immunofluorescence staining of FCoV antigen in macrophages of effusions (n = 11), or by both methods (n = 4). Forty-nine control cats had other diseases but similar clinical signs. Real-time RT-PCR was performed on PBMCs of 37 cats (21 cats with FIP, 16 controls), on serum of 51 cats (26 cats with FIP, 25 controls) and on cell-free body cavity effusion of 69 cats (36 cats with FIP, 33 controls). Sensitivity, specificity, positive and negative predictive value, including 95% confidence intervals (CI), were calculated. Results Real-time RT-PCR of PBMCs, serum and cell-free body cavity effusion showed a specificity of 100% (95% CI 79.4-100% in PBMCs, 86.3-100% in serum, 89.4-100% in cell-free body cavity effusion) and a sensitivity of 28.6% (95% CI 11.3-52.2%) in PBMCs, 15.4% (95% CI 4.4-34.9%) in serum and 88.9% (95% CI 73.9-96.9%) in cell-free body cavity effusion to diagnose FIP. Conclusions and relevance Although it is known that RT-PCR can often provide false-positive results in healthy cats, this real-time RT-PCR was shown to be a specific tool for the diagnosis of FIP when applied in a clinical setting. Sensitivity in cell-free body cavity effusion was high but low in PBMCs and serum. PBMC samples showed a higher sensitivity than serum samples, and are therefore a better choice if no effusion is present.

Detection of feline coronavirus spike gene mutations as a tool to diagnose feline infectious peritonitis

Objectives Feline infectious peritonitis (FIP) is an important cause of death in the cat population worldwide. The ante-mortem diagnosis of FIP in clinical cases is still challenging. In cats without effusion, a definitive diagnosis can only be achieved post mortem or with invasive methods. The aim of this study was to evaluate the use of a combined reverse transcriptase nested polymerase chain reaction (RT-nPCR) and sequencing approach in the diagnosis of FIP, detecting mutations at two different nucleotide positions within the spike (S) gene. Methods The study population consisted of 64 cats with confirmed FIP and 63 cats in which FIP was initially suspected due to similar clinical or laboratory signs, but that were definitively diagnosed with another disease. Serum/plasma and/or effusion samples of these cats were examined for feline coronavirus (FCoV) RNA by RT-nPCR and, if positive, PCR products were sequenced for nucleotide transitions within the S gene. Results Specificity of RT-nPCR was 100% in all materials (95% confidence interval [CI] in serum/plasma 83.9-100.0; 95% CI in effusion 93.0-100.0). The specificity of the sequencing step could not be determined as none of the cats of the control group tested positive for FCoV RNA. Sensitivity of the 'combined RT-nPCR and sequencing approach' was 6.5% (95% CI 0.8-21.4) in serum/plasma and 65.3% (95% CI 50.4-78.3) in effusion. Conclusions and relevance A positive result is highly indicative of the presence of FIP, but as none of the control cats tested positive by RT-nPCR, it was not possible to confirm that the FCoV mutant described can only be found in cats with FIP. Further studies are necessary to evaluate the usefulness of the sequencing step including FCoV-RNA-positive cats with and without FIP. A negative result cannot be used to exclude the disease, especially when only serum/plasma samples are available.

Investigation into the utility of an immunocytochemical assay in body cavity effusions for diagnosis of feline infectious peritonitis

Objectives Feline coronaviruses (FCoVs) exist as two biotypes, feline enteric coronavirus and feline infectious peritonitis virus. Although feline infectious peritonitis (FIP) is a very common disease, the ante-mortem diagnosis of this disease still remains a challenge. Immunofluorescence staining of FCoV in macrophages in effusion has been considered as the reference standard for the diagnosis, but recently this method has been shown to have lower specificity than previously reported. In addition, this method is not widely available and requires the use of fluorescence microscopes. Therefore, it was the aim of this study to evaluate the diagnostic potential of an immunocytochemical (ICC) assay using body cavity effusion. Methods Effusion samples from 27 cats with immunohistochemically confirmed FIP and 29 cats with suspected FIP but a definitive diagnosis of another disease were examined. ICC specimens were evaluated with respect to positive immunostaining. In addition, effusion samples were stained with haematoxylin and eosin and evaluated cytologically. Results A diagnostic sensitivity of 85.2% was recorded for effusion specimens (95% confidence interval [CI] 66.3-95.8), while the diagnostic specificity was only 72.4% (95% CI 52.8-87.3). Conclusions and relevance Once the clinical disease of FIP develops in a cat, it always leads to death, and most of the cats are euthanased within a few days or weeks. As false-positive results might lead to euthanasia of cats suffering from potentially treatable diseases, the diagnostic specificity of a diagnostic tool is the most important factor in a fatal disease like FIP. Thus, the diagnostic utility of this test proved to be insufficient and positive ICC results should be interpreted with caution. Nevertheless, full-body necropsy could not be performed in 13/29 control cats. It is possible that these cats actually suffered from early-stage FIP and that this fact might have influenced the diagnostic specificity of the ICC. Based on the results of the present study, however, ICC of effusion samples currently cannot be recommended to confirm a suspicion of FIP.

Diagnosing feline infectious peritonitis using the Sysmex XT-2000iV based on frozen supernatants from cavitary effusions

The delta total nucleated cells (ΔTNC) measurement with the Sysmex XT-2000iV (Sysmex Europe, Norderstedt, Germany) has high diagnostic accuracy on effusions in feline infectious peritonitis (FIP) cases, but the test can be performed only on fresh samples. We evaluated whether supernatants from effusions retain the ability to induce cell clumping and assessed the diagnostic accuracy of this modified ΔTNC method. Effusions were collected from FIP cats ( n = 19) and from cats with other diseases ( n = 15). ΔTNC was measured on fresh samples and on frozen-thawed supernatants after the addition of feline blood at 1:10 dilution. Diagnostic accuracy was assessed at the cutoffs of suggestive of FIP (ΔTNC = 1.7) and consistent with FIP (ΔTNC = 3.4). The influence of the protein content, number of added cells, and magnitude of dilution were also investigated. Specificity and positive predictive value were 100% for both the methods. Sensitivity and negative predictive value were higher for the modified ΔTNC (84.2% and 83.3%, respectively, at the cutoff of 1.7; 78.9% and 78.9%, respectively, at the cutoff of 3.4) than for the ΔTNC on fresh samples (78.6% and 81.3%, respectively, at the cutoff of 1.7; 57.1% and 68.4%, respectively, at the cutoff of 3.4). Protein content, total cell count of the added blood, and magnitude of dilutions did not influence the results. Supernatants of frozen effusions from FIP cats retain the ability to induce cell clumping, thus the modified ΔTNC measurement is a reliable tool to diagnose FIP on samples that cannot be analyzed immediately.

Polyprenyl Immunostimulant Treatment of Cats with Presumptive Non-Effusive Feline Infectious Peritonitis In a Field Study

Feline infectious peritonitis (FIP) is a fatal disease with no clinically effective treatment. This field study evaluated treatment with Polyprenyl Immunostimulant (PI) in cats with the non-effusive form of FIP. Because immune suppression is a major component in the pathology of FIP, we hypothesized that treatment with an immune system stimulant would increase survival times of cats with dry FIP. Sixty cats, diagnosed with dry FIP by primary care and specialist veterinarians and meeting the acceptance criteria, were treated with PI without intentional selection of less severe cases. The survival time from the start of PI treatment in cats diagnosed with dry FIP showed that of the 60 cats with dry FIP treated with PI, 8 survived over 200 days, and 4 of 60 survived over 300 days. A literature search identified 59 cats with non-effusive or dry FIP; no cat with only dry FIP lived longer than 200 days. Veterinarians of cats treated with PI that survived over 30 days reported improvements in clinical signs and behavior. The survival times in our study were significantly longer in cats who were not treated with corticosteroids concurrently with PI. While not a cure, PI shows promise in the treatment of dry form FIP, but a controlled study will be needed to verify the benefit.

Ultrasonographic, endoscopic and histological appearance of the caecum in clinically healthy cats

Objectives The aim of the study was to describe the ultrasonographic and endoscopic appearance and characteristics of the caecum in asymptomatic cats, and to correlate these findings with histology. Methods Ex vivo ultrasonographic and histologic evaluations of a fresh caecum were initially performed. Then, 20 asymptomatic cats, privately owned or originating from a reproductive colony, were recruited. All cats had an ultrasonographic examination of the ileocaecocolic junction, where the thickness of the caecal wall, ileocolic lymph nodes and the echogenicity of the local fat were assessed. They all underwent a colonoscopy with a macroscopic assessment of the mucosa and biopsies for histology. Results An ultrasonographic hypoechoic nodular inner layer, which corresponded to the coalescence of multiple lymphoid follicles originating from the submucosa and protruding in the mucosa on histology, was visible in all parts of the caecum. The combined mucosa and submucosa was measured ultrasonographically and defined as the follicular layer. Although all cats were asymptomatic, 3/19 cats showed mild caecal inflammation on histology. The most discriminatory ultrasonographic parameter in assessing this subclinical inflammation was the thickness of the follicular layer at the entrance of the caecum, with a cut-off value of 2.0 mm. All cats (20/20) showed some degree of macroscopic 'dimpling' of the caecal mucosa on endoscopy. Conclusions and relevance Lymphoid follicles in the caecal mucosa and submucosa constitute a unique follicular layer on ultrasound. In asymptomatic cats, a subtle, non-clinically relevant inflammation may exist and this is correlated with an increased thickness of the follicular layer on ultrasound. On endoscopy, a 'dimpled aspect' to the caecal mucosa is a normal finding in the asymptomatic cat.

Ultrasonographic, endoscopic and histological appearances of the caecum in cats presenting with chronic clinical signs of caecocolic disease

Objectives This study aimed to describe the ultrasonographic, endoscopic and histological characteristics of the caecum and ileocaecocolic junction in cats suffering from chronic clinical signs compatible with caecocolic disease. Methods Cats presenting with clinical signs suggestive of a caecocolic disease were prospectively recruited. All cats underwent an ultrasonographic examination of the caecum, ileum, colon, ileocolic lymph nodes and local mesenteric fat, in addition to comprehensive abdominal ultrasonography. This was followed by a colonoscopy with a macroscopic assessment of the caecocolic mucosa; caecocolic tissue samples were systematically collected for histologic analysis. Results Eighteen cats were included. Eleven of 18 cats had ultrasonographic abnormalities adjacent to the ileocaecocolic junction (lymphadenopathy, local steatitis) and 13/18 cats had abnormalities directly related to the junction (wall thickening, loss of wall layering). Seventeen of 18 cats had at least one ultrasonographic abnormality. Endoscopically, hyperaemia, oedema, discoloration and/or erosions were found in all cats. Each cat was classified as having mild or moderate-to-severe lesions according to endoscopic results; no classification could be established statistically for ultrasonographic results. The accentuation of the dimpled pattern tended to be inversely related to the severity of endoscopic lesion scoring. Histologically, a large proportion of cats showed typhlitis (13/16), one had lymphoma and two were normal. All cats with typhlitis also had colitis. There was only slight agreement between endoscopic and histological caecal results regarding the severity of lesions. Loss of caecal wall layering on ultrasound was found in 7/18 cats and, surprisingly, did not appear as a reliable predictor of the severity of inflammation or of malignancy; neither did local steatitis nor lymph node size. Conclusions and relevance Ultrasonography and endoscopy should not be used as the sole methods to investigate the ileocaecocolic region in cats with clinical signs suggestive of caecocolic disease. The presence of chronic clinical signs should routinely prompt histological biopsy.

Reverse transcriptase loop-mediated isothermal amplification for the detection of feline coronavirus

The Feline coronavirus (FCoV) is the etiological agent of feline infectious peritonitis (FIP), a lethal disease of felids. The role of molecular methods is controversial for the diagnosis of FIP, while essential for the identification of the shedders. Thus, a fast and inexpensive method for the detection of FCoV could be beneficial, especially in multicat environments. A reverse transcription loop mediated isothermal amplification (RT-LAMP) assay was developed. RNA extraction and RT-nPCR for FCoV were performed on thirty-two samples (11 faeces, 9 blood, 8 effusions, and 4 lymph nodes) collected from 27 cats. Six RT-LAMP primers were designed from the same conserved region of RT-nPCR, and the assay was run at 63°C for one hour. Results were evaluated through both agarose gel run and hydroxynapthol blue (HNB) dye and then compared with RT-nPCR results for the assessment of sensitivity and specificity. The overall specificity was 100%, but the sensitivity was 50% and 54.5% for agarose gel and HNB respectively. Therefore, RT-LAMP seems optimal to confirm the presence of the virus, but not applicable to exclude it.

Clinical and laboratory features of cats with feline infectious peritonitis--a retrospective study of 231 confirmed cases (2000-2010)

OBJECTIVES

The objectives of this study were to review signalment, clinical signs and laboratory features in a large number of naturally occurring cases of feline infectious peritonitis (FIP), and to evaluate potential changes in diagnostic criteria for FIP and compare findings in cats with and without effusion.

METHODS

The medical records of 231 cats with confirmed FIP that presented to the Clinic of Small Animal Medicine of the Ludwig-Maximilian University of Munich, Germany, were reviewed for signalment, history, and clinical and laboratory parameters. Age, sex and breed distribution of the cats were compared with the clinic population.

RESULTS

Male sex and young age were significantly correlated with FIP. Neutering status was not associated with FIP. No breed predisposition was observed and the majority of cats presented were domestic shorthair and mixed breed. Microcytosis of peripheral erythrocytes was found in 35.1% of cats, of which 42.4% did not have concurrent anaemia. Band neutrophilia was documented in 44.3% (81/183), of which 35.8% did not have mature neutrophilia. Lymphopenia, observed significantly more often with effusion, was documented in only 26.8% of cats without effusion. Hyperbilirubinaemia also occurred significantly more often in cats with vs without effusion. While serum total protein was increased in only 17.5% of cats, hyperglobulinaemia was documented in 89.1%. Nearly 85.0% of cats had an albumin-to-globulin (A:G) ratio <0.8, while 67.8% had an A:G ratio <0.6.

CONCLUSIONS AND RELEVANCE

Microcytosis was common and can increase suspicion of FIP in the presence of other typical clinical and laboratory abnormalities. The low prevalence of lymphopenia in cats without effusion suggests that this is not a useful parameter in non-effusive FIP. The frequent occurrence of a left shift in the absence of a mature neutrophilia complicates the differentiation of effusive FIP and septic peritonitis. Globulins and A:G ratio were of higher diagnostic value than hyperproteinaemia.