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

Practical approach to development of GS-445124-loaded PLGA nanoparticles for the long-term treatment of feline infectious peritonitis caused by feline coronavirus infection

Feline infectious peritonitis virus (FIPV) caused by feline coronavirus (FCoV) infection leads to a high mortality rate when untreated. GS-441524, an antiviral agent effective against FIPV, is orally administered twice daily or through daily subcutaneous injections for approximately 12 weeks. While the short treatment period recuses concerns about adherence, frequent administrations may cause handling-related stress in cats. Therefore, it is essential to develop a long-acting formulation that requires only a single administration. In this study, we used polylactide-co-glycolide (PLGA) as a carrier, which was used to effectively encapsulate GS-441524 with sustained-release functionality and GS-441524-loaded PLGA nanoparticles (GS-PLGA NP) were prepared. The particle size of GS-PLGA NP was 216 nm, the encapsulation efficiency was 78 %, and the 7-day release was 92 %. When GS-PLGA NP was injected at 22 mg/kg in cats, higher systemic exposure can be expected compared to injecting GS-441524 at 4 mg/kg for one week (relative bioavailability, 152 %). As well as GS-PLGA NP showed lower toxicity, improved cellular uptake, and enhanced antiviral efficacy against FCoV compared to the pure GS-441524.

[Feline infectious peritonitis - a current overview]

Coronaviruses (CoVs) are positive, single-stranded RNA viruses that can infect various animal species as well as humans. Particularly relevant for cats is the feline coronavirus (FCoV), which is widespread in cat populations worldwide. Infection with FCoV is usually asymptomatic. However, in multi-cat households, approximately 5-12% of FCoV-infected cats develop feline infectious peritonitis (FIP) due to mutations in the spike gene. FIP is an immune-mediated disease that previously was always fatal. These mutations result in a tropism shift from enterocytes to monocytes and macrophages. The associated change in the virulence of FCoV leads to the characteristic granulomatous vasculitis and perivasculitis observed in FIP. Recently, significant advancements have been made in understanding FIP. Studies show that antiviral drugs used in human medicine, such as the nucleoside analog GS-441524, are effective against FIP and can provide affected cats with a survival chance of up to 100%. Additionally, a novel FCoV variant, FCoV-23, has been identified in cats from Cyprus. According to newest research, this virus arose through a recombination between FCoV and the highly virulent pantropic canine coronavirus; it can be directly transmitted from cat to cat and lead to FIP. Furthermore, increasing evidence suggests that FIP is frequently associated with myocarditis. This article provides an overview of the current knowledge on FIP, including its pathology, clinical signs, effective treatment options, and preventive measures.

A review of feline infectious peritonitis virus infection

Feline infectious peritonitis (FIP) is an infectious disease characterized by non-specific laboratory changes and clinical signs. Clinical symptoms include anorexia, jaundice, fever, and weight loss. Moreover, some lesions are found in the digestive and respiratory systems. FIP, whose virulence varies, cannot be distinguished using several diagnostic methods. Moreover, feline coronaviruses (FCoVs) can be classified into two serotypes based on differences in their amino acid sequences, spike (S) protein sequences, and antibody (Ab) neutralization. There are two pathotypes, namely those caused by FCoV, which are often referred to as feline enteric coronavirus and FIP virus (FIPV). Furthermore, FIPV infection can be caused by sub-neutralizing levels of anti-FIPV S Abs. Therefore, a supporting diagnosis is needed to confirm FIP because there are no specific symptoms. This review aimed to provide updated information on FIP, including epizootiology, clinical and pathological characteristics, pathogenesis, hematology, clinicopathological and imaging features, pathological features, experimental infection, treatment and prevention, infection and immunity, animal and public health considerations.

Complement Evasion Protects FCoV from Virus Clearance Within Prototypic FIP Lesions

Feline infectious peritonitis (FIP) is a fatal disease in cats caused by infection with feline coronavirus (FCoV). Despite severe inflammatory changes, defense mechanisms fail to achieve virus clearance. Some studies focused on various immune evasion mechanisms, but none of these studies elucidated the inefficacy of the complement system, which is one major player in FIP-associated immune pathogenesis. This study aimed to investigate the involvement of complement-regulating factors (CRFs). CRFs help modulate the immune response and prevent host tissue damage. Archived tissue samples from 31 deceased, FIP-affected cats were evaluated using multiplex immunohistochemistry for the spatial expression of the complement-regulating factors CD46 and CD59 in association with FIP lesions and their colocalization with complement-activating factor C1q and membrane attack complex C9 in relation to the presence and proximity of FCoV-infected cells. The FIP lesions of all 31 cats exhibited marked expression of both complement-regulating factors in proximity to FCoV-infected macrophages. Moreover, their expression in all 31 animals was significantly lower than the expression of the complement-activating factors C1q and C9 compared to areas farther distal to FCoV-infected cells. In conclusion, FCoV-infected macrophages in cats with FIP appear to use autocrine and paracrine expression of complement-regulating factors in their immediate environment to shield themselves from destruction by the complement system.

Protoporphyrin IX-Dependent Antiviral Effects of 5-Aminolevulinic Acid against Feline Coronavirus Type II

5-Aminolevulinic acid (5-ALA), a non-proteinogenic amino acid, is an intermediate in the biosynthesis of heme and exerts antiviral effects against feline coronavirus (FCoV); however, the underlying mechanisms remain unclear. In the biosynthesis of heme, 5-ALA is condensed and converted to protoporphyrin IX (PpIX), which is then transformed into heme by the insertion of ferrous iron. Previous research has suggested that the metabolites generated during heme biosynthesis contribute to the antiviral effects of 5-ALA. Therefore, the present study investigated the in vitro mechanisms responsible for the antiviral effects of 5-ALA. The results obtained revealed that 5-ALA and PpIX both effectively reduced the viral titer in the supernatant of FCoV-infected fcwf-4 cells. Moreover, PpIX exerted virucidal effects against FCoV. We also confirmed that 5-ALA increased PpIX levels in cells. While hemin induced heme oxygenase-1 gene expression, it did not reduce the viral titer in the supernatant. Sodium ferrous citrate decreased PpIX levels and suppressed the antiviral effects of 5-ALA. Collectively, these results suggest that the antiviral effects of 5-ALA against FCoV are dependent on PpIX.

GS-441524 and molnupiravir are similarly effective for the treatment of cats with feline infectious peritonitis

Although not registered for feline infectious peritonitis (FIP) in Japan, nucleoside analogs have shown efficacy and we have been offering them to owners of cats with FIP at our clinic since January 2020. The aim of this study was to investigate outcomes in cats with FIP who received GS-441524 or molnupiravir. Diagnosis of FIP was based on clinical signs, laboratory test results, and the presence of feline coronavirus RNA in blood or effusion aspirate. After providing verbal and written information, owners of cats with a presumptive diagnosis of FIP with a were offered antiviral treatment with commercially sourced GS-441524 from June 2020, and either GS-441524 or compounded molnupiravir from January 2022. Dosing was 12.5-25 mg/kg/day for GS-441524 and 20-40 mg/kg/day for molnupiravir, depending on the presence of effusion and neurological and/or ocular signs, and continued for 84 days. Overall, 118 cats with FIP (effusive in 76) received treatment, 59 with GS-4421524 and 59 with molnupiravir. Twenty cats died, 12/59 (20.3%) in the GS-441524 group and 8/59 (13.6%) in the molnupiravir group (p = 0.326), with most deaths within the first 10 days of starting treatment. Among survivors, neurological and ocular signs resolved in all but one cat, who had persistent seizures. Of the cats completing treatment, 48/48 in the GS-441524 group and 51/52 in the molnupiravir group achieved remission. Laboratory parameters normalized within 6 to 7 weeks of starting drug administration. Adverse events, such as primarily hepatic function abnormalities, were transient and resolved without specific intervention. Our data indicate that GS-441524 and molnupiravir show similar effects and safety in cats with FIP.

Short Treatment of 42 Days with Oral GS-441524 Results in Equal Efficacy as the Recommended 84-Day Treatment in Cats Suffering from Feline Infectious Peritonitis with Effusion-A Prospective Randomized Controlled Study

In the past, feline infectious peritonitis (FIP) caused by feline coronavirus (FCoV) was considered fatal. Today, highly efficient drugs, such as GS-441524, can lead to complete remission. The currently recommended treatment duration in the veterinary literature is 84 days. This prospective randomized controlled treatment study aimed to evaluate whether a shorter treatment duration of 42 days with oral GS-441524 obtained from a licensed pharmacy is equally effective compared to the 84-day regimen. Forty cats with FIP with effusion were prospectively included and randomized to receive 15 mg/kg of GS-441524 orally every 24h (q24h), for either 42 or 84 days. Cats were followed for 168 days after treatment initiation. With the exception of two cats that died during the treatment, 38 cats (19 in short, 19 in long treatment group) recovered with rapid improvement of clinical and laboratory parameters as well as a remarkable reduction in viral loads in blood and effusion. Orally administered GS-441524 given as a short treatment was highly effective in curing FIP without causing serious adverse effects. All cats that completed the short treatment course successfully were still in complete remission on day 168. Therefore, a shorter treatment duration of 42 days GS-441524 15 mg/kg can be considered equally effective.

Adapting the SMART tube technology for flow cytometry in feline full blood samples

Flow cytometry of blood samples is a very valuable clinical and research tool to monitor the immune response in human patients. Furthermore, it has been successfully applied in cats, such as for infections with feline immune deficiency virus (FIV). However, if cells are not isolated and frozen, analysis of anticoagulated blood samples requires mostly prompt processing following blood collection, making later analysis of stored full blood samples obtained in clinical studies often impossible. The SMART Tube system (SMART TUBE Inc., California, United States; SMT) allows fixation and long-term preservation of whole blood samples at -80°C. However, this system has so far only been applied to human biological samples. In the present study, a new flow cytometry SMART Tube protocol adapted for feline whole blood samples was successfully established allowing quantification of T-helper cells, cytotoxic T-cells, B-cells, monocytes, and neutrophils up to 2 years post sampling. Results obtained from frozen stabilized and fresh blood samples were compared for validation purposes and correlated to differential blood counts from a conventional hematology analyzer. Clinical applicability of the new technique was verified by using samples from a treatment study for feline infectious peritonitis (FIP). Using the new SMT protocol on retained samples, it could be demonstrated that long-term storage of these SMT tubes is also possible. In summary, the newly adapted SMT protocol proved suitable for performing flow cytometry analysis on stored feline whole blood samples, thus opening up new avenues for veterinary research on a variety of aspects of clinical interest.

Alpha-1-Acid Glycoprotein Quantification via Spatial Proximity Analyte Reagent Capture Luminescence Assay: Application as Diagnostic and Prognostic Marker in Serum and Effusions of Cats with Feline Infectious Peritonitis Undergoing GS-441524 Therapy

Until recently, the diagnosis of feline infectious peritonitis (FIP) in cats usually led to euthanasia, but recent research has revealed that antiviral drugs, including the nucleoside analog GS-441524, have the potential to effectively cure FIP. Alpha-1-acid glycoprotein (AGP) has been suggested as a diagnostic marker for FIP. However, AGP quantification methods are not easily accessible. This study aimed to establish a Spatial Proximity Analyte Reagent Capture Luminescence (SPARCLTM) assay on the VetBio-1 analyzer to determine the AGP concentrations in feline serum and effusion samples. Linearity was found in serial dilutions between 1:2000 and 1:32,000; the intra-run and inter-run precision was <5% and <15%, respectively; and AGP was stable in serum stored for at least 8 days at room temperature, at 4 °C and at -20 °C. Cats with confirmed FIP had significantly higher serum AGP concentrations (median: 2954 µg/mL (range: 200-5861 µg/mL)) than those with other inflammatory diseases (median: 1734 µg/mL (305-3449 µg/mL)) and clinically healthy cats (median 235 µg/mL (range: 78-616 µg/mL); pKW < 0.0001). The AGP concentrations were significantly higher in the effusions from cats with FIP than in those from diseased cats without FIP (pMWU < 0.0001). The AGP concentrations in the serum of cats with FIP undergoing GS-441524 treatment showed a significant drop within the first seven days of treatment and reached normal levels after ~14 days. In conclusion, the VetBio-1 SPARCLTM assay offers a precise, fast and cost-effective method to measure the AGP concentrations in serum and effusion samples of feline patients. The monitoring of the AGP concentration throughout FIP treatment provides a valuable marker to evaluate the treatment's effectiveness and identify potential relapses at an early stage.

Serologic, Virologic and Pathologic Features of Cats with Naturally Occurring Feline Infectious Peritonitis Enrolled in Antiviral Clinical Trials

Feline infectious peritonitis (FIP) is a multisystemic, generally lethal immuno-inflammatory disease of domestic cats caused by an infection with a genetic variant of feline coronavirus, referred to as the FIP virus (FIPV). We leveraged data from four different antiviral clinical trials performed at the University of California, Davis. Collectively, a total of 60 client-owned domestic cats, each with a confirmed diagnosis of naturally occurring FIP, were treated with a variety of antiviral compounds. The tested therapies included the antiviral compounds GS-441524, remdesivir, molnupiravir and allogeneic feline mesenchymal stem/stroma cell transfusions. Four client-owned cats with FIP did not meet the inclusion criteria for the trials and were not treated with antiviral therapies; these cats were included in the data set as untreated FIP control cats. ELISA and Western blot assays were performed using feline serum/plasma or ascites effusions obtained from a subset of the FIP cats. Normalized tissue/effusion viral loads were determined in 34 cats by a quantitative RT-PCR of nucleic acids isolated from either effusions or abdominal lymph node tissue. Twenty-one cats were PCR "serotyped" (genotyped) and had the S1/S2 region of the coronaviral spike gene amplified, cloned and sequenced from effusions or abdominal lymph node tissue. In total, 3 untreated control cats and 14 (23.3%) of the 60 antiviral-treated cats died or were euthanized during (13) or after the completion of (1) antiviral treatment. Of these 17 cats, 13 had complete necropsies performed (10 cats treated with antivirals and 3 untreated control cats). We found that anticoronaviral serologic responses were persistent and robust throughout the treatment period, primarily the IgG isotype, and focused on the viral structural Nucleocapsid and Membrane proteins. Coronavirus serologic patterns were similar for the effusions and serum/plasma of cats with FIP and in cats entering remission or that died. Viral RNA was readily detectable in the majority of the cats in either abdominal lymph node tissue or ascites effusions, and all of the viral isolates were determined to be serotype I FIPV. Viral nucleic acids in cats treated with antiviral compounds became undetectable in ascites or abdominal lymph node tissue by 11 days post-treatment using a sensitive quantitative RT-PCR assay. The most common pathologic lesions identified in the necropsied cats were hepatitis, abdominal effusion (ascites), serositis, pancreatitis, lymphadenitis, icterus and perivasculitis. In cats treated with antiviral compounds, gross and histological lesions characteristic of FIP persisted for several weeks, while the viral antigen became progressively less detectable.

An adenovirus-vectored vaccine based on the N protein of feline coronavirus elicit robust protective immune responses

Feline coronavirus (FCoV) is an unsegmented, single-stranded RNA virus belonging to the Alphacoronavirus genus. It can cause fatal feline infectious peritonitis (FIP) in cats of any ages. Currently, there are no effective prevention and control measures to against FCoV. In this study, we developed a recombinant adenovirus vaccine, AD5-N, based on the nucleocapsid(N) protein of FCoV. The immunogenicity of AD5-N was evaluated through intramuscular immunization in 6-week-old Balb/c mice and 9-12 months old cats. Compared to the control group, AD5-N specifically induced a significant increase in IgG and SIgA levels in the vaccinated mice. Furthermore, AD5-N not only effectively promoted strong cellular immune responses in cats but also induced high levels of specific SIgA, effectively helping cats resist FCoV infection. Our findings suggest that adenovirus vector vaccines based on the N gene have the potential to become candidate vaccines for the prevention and control of FCoV infection.

Analysis of spike and accessory 3c genes mutations of less virulent and FIP-associated feline coronaviruses in Beijing, China

Mutations in S and 3c genes of feline coronavirus (FCoV) have been associated with the development of feline infectious peritonitis (FIP). In the present study, FCoV S and 3c genes mutations were analyzed in healthy and FIP cats. M1058L mutation was found in 13.64% (3/22) feces from FIP cats, but not in feces from healthy cats (0/39). The intact 3c gene was found in feces from both healthy cats (19/19) and FIP cats (12/12). All parenteral samples from FIP cats carried one or more of the M1058L mutation, S1060A mutation and mutated 3c gene. FCoV reverse-transcriptase polymerase chain reaction (RT-PCR) of parenteral samples (including ascites, pleural effusions and tissue) is recommended as the gold standard for clinical diagnosis of FIP rather than detection of the M1058L mutation, but when cats have severe gastrointestinal symptoms and lesions, detection of the M1058L mutation in feces may be helpful in diagnosing FIP.

[Options for treatment of feline infectious peritonitis - previously and today]

Feline infectious peritonitis (FIP) is one of the most common infectious diseases in cats that is fatal when untreated. So far, there is no legally available effective treatment in Germany. Treatment options include only symptomatic treatment (e. g. glucocorticoids, propentofylline), immunomodulatory approaches (e. g. interferons, polyprenyl immunostimulant), and antiviral chemotherapy with protease inhibitors (e. g. GC376) or nucleoside analogues (e. g. GS-441524, remdesivir). Symptomatic treatment does not cure FIP but may lead to a short-term improvement of clinical signs in a subset of cats. Immunomodulatory treatment has also not shown to be very promising. In contrary, the antiviral compounds GS-441524 and GC376 exhibited significant efficacy in several studies and their use saved the lives of many cats suffering from FIP. However, both agents are currently not licensed and thus cannot be legally administered by veterinarians in Germany. Legally, cats may only be legally treated with GS-441524 in a few countries (e.g. Great Britain and Australia). In other countries, GS-441524 is imported by cat owners via the black market and administered on their own. This article provides an overview of the available treatment options and an outlook on the legal use of effective antiviral drugs.

Feline Infectious Peritonitis: European Advisory Board on Cat Diseases Guidelines

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

Intra-host variation in the spike S1/S2 region of a feline coronavirus type-1 in a cat with persistent infection

Feline coronavirus type 1 (FCoV-1) is widely known for causing feline infectious peritonitis (FIP), a systemic infection that is often fatal, with the virus known as the FIPV biotype. However, subclinical disease also occurs, in which cats may not show signs and intermittently shed the virus, including in feces, possibly for long periods of time. This virus is known as the FECV biotype. Progression of FECV to FIPV has been linked to several genomic changes, however a specific region of the viral spike protein at the interface of the spike S1 and S2 domains has been especially implicated. In this study, we followed a cat (#576) for six years from 2017, at which time FCoV-1 was detected in feces and conjunctival swabs, until 2022, when the animal was euthanized based on a diagnosis of alimentary small cell lymphoma. Over this time period, the cat was clinically diagnosed with inflammatory bowel disease and chronic rhinitis, and cardiac problems were also suspected. Using hybridization capture targeting the spike (S) gene of FCoV followed by next-generation sequencing, we screened 27 clinical samples. We detected FCoV-1 in 4 samples taken in 2017 (intestine and nasal tissue, feces, and conjunctiva), and 3 samples taken in 2022 (feces, and intestinal and heart tissue), but not in fecal samples taken in 2019 and 2020. Next, we focused on the S1/S2 region within S, which contains the furin cleavage site (FCS), a key regulator of viral transmission and pathogenesis. We show that the FCoV-1 variants obtained from feces in 2017 and 2022 were identical, while the ones from conjunctiva (2017), heart (2022), and intestine (2017 and 2022) were distinct. Sequence comparison of all the variants obtained showed that most of the non-synonymous changes in the S1/S2 region occur within the FCS. In the heart, we found two variants that differed by a single nucleotide, resulting in distinct FCS motifs that differ in one amino acid. It is predicted that one of these FCS motifs will down-regulate spike cleavability. The variant from the conjunctiva (2017) had a 6-nucleotide in-frame insertion that resulted in a longer and more exposed S1/S2 loop, which is predicted to be more accessible to the furin protease. Our studies indicate that FCoV-1 can independently persist in the gastrointestinal tract and heart of a cat over a long period of time without evidence of typical FIP signs, with intermittent viral shedding from the gastrointestinal and respiratory tracts.

Long-term follow-up of cats in complete remission after treatment of feline infectious peritonitis with oral GS-441524

OBJECTIVES

Feline infectious peritonitis (FIP), a common disease in cats caused by feline coronavirus (FCoV), is usually fatal once clinical signs appear. Successful treatment of FIP with oral GS-441524 for 84 days was demonstrated recently by this research group. The aim of this study was to evaluate the long-term outcome in these cats.

METHODS

A total of 18 successfully treated cats were followed for up to 1 year after treatment initiation (9 months after completion of the antiviral treatment). Follow-up examinations were performed at 12-week intervals, including physical examination, haematology, serum biochemistry, abdominal and thoracic ultrasound, FCoV ribonucleic acid (RNA) loads in blood and faeces by reverse transciptase-quantitative PCR and anti-FCoV antibody titres by indirect immunofluorescence assay.

RESULTS

Follow-up data were available from 18 cats in week 24, from 15 cats in week 36 and from 14 cats in week 48 (after the start of treatment), respectively. Laboratory parameters remained stable after the end of the treatment, with undetectable blood viral loads (in all but one cat on one occasion). Recurrence of faecal FCoV shedding was detected in five cats. In four cats, an intermediate short-term rise in anti-FCoV antibody titres was detected. In total, 12 cats showed abdominal lymphadenomegaly during the follow-up period; four of them continuously during the treatment and follow-up period. Two cats developed mild neurological signs, compatible with feline hyperaesthesia syndrome, in weeks 36 and 48, respectively; however, FCoV RNA remained undetectable in blood and faeces, and no increase in anti-FCoV antibody titres was observed in these two cats, and the signs resolved.

CONCLUSIONS AND RELEVANCE

Treatment with GS-441524 proved to be effective against FIP in both the short term as well as the long term, with no confirmed relapse during the 1-year follow-up period. Whether delayed neurological signs could be a long-term adverse effect of the treatment or associated with a 'long FIP syndrome' needs to be further evaluated.

Patterns of Feline Coronavirus Shedding and Associated Factors in Cats from Breeding Catteries

(1) Background: In households in which feline coronavirus (FCoV) is present, three patterns of FCoV shedding are described: non-shedders, intermittent (low-intensity) shedders, or persistent (high-intensity) shedders. It was the aim of this study to describe FCoV shedding patterns in cats from catteries in which FCoV infection is endemic. Additionally, risk factors for high-intensity FCoV shedding or non-shedding were analyzed. (2) Methods: Four fecal samples of 222 purebred cats from 37 breeding catteries were examined for FCoV RNA by quantitative reverse transcription polymerase chain reaction (RT-qPCR). High-intensity shedders were defined as cats positive for FCoV RNA in at least 3/4 fecal samples; non-shedding cats were defined as cats negative in all four fecal samples. Risk factor analysis was performed using information obtained by questionnaire. (3) Results: Of the 222 cats, 125 (56.3%) were considered high-intensity shedders, while 54/222 cats (24.3%) were FCoV non-shedders. The Persian breed was associated with a higher risk of high-intensity shedding in multivariable analysis, while Birman and Norwegian Forest Cats were more likely to be FCoV non-shedders. Cats living together with other cats were more likely to be FCoV shedders. (4) Conclusions: The proportion of both high-intensity shedders and non-shedding cats was higher than previously reported, which possibly can be explained by housing conditions, different genetic susceptibility, or differences in the study period. The risk of high-intensity shedding is higher in certain breeds. However, it cannot be excluded that the individual hygiene procedure of each breeder influenced FCoV-shedding frequency. A smaller group size is a protective factor against FCoV shedding.

Stopping Feline Coronavirus Shedding Prevented Feline Infectious Peritonitis

After an incubation period of weeks to months, up to 14% of cats infected with feline coronavirus (FCoV) develop feline infectious peritonitis (FIP): a potentially lethal pyogranulomatous perivasculitis. The aim of this study was to find out if stopping FCoV faecal shedding with antivirals prevents FIP. Guardians of cats from which FCoV had been eliminated at least 6 months earlier were contacted to find out the outcome of their cats; 27 households were identified containing 147 cats. Thirteen cats were treated for FIP, 109 cats shed FCoV and 25 did not; a 4-7-day course of oral GS-441524 antiviral stopped faecal FCoV shedding. Follow-up was from 6 months to 3.5 years; 11 of 147 cats died, but none developed FIP. A previous field study of 820 FCoV-exposed cats was used as a retrospective control group; 37 of 820 cats developed FIP. The difference was statistically highly significant (p = 0.0062). Cats from eight households recovered from chronic FCoV enteropathy. Conclusions: the early treatment of FCoV-infected cats with oral antivirals prevented FIP. Nevertheless, should FCoV be re-introduced into a household, then FIP can result. Further work is required to establish the role of FCoV in the aetiology of feline inflammatory bowel disease.

An updated review of feline coronavirus: mind the two biotypes

Feline coronavirus (FCoV) includes two biotypes: feline infectious peritonitis virus (FIPV) and feline enteric coronavirus (FECV). Although both biotypes can infect cats, their pathogenicities differ. The FIPV biotype is more virulent than the FECV biotype and can cause peritonitis or even death in cats, while most FECV biotypes do not cause lesions. Even pathogenic strains of the FECV biotype can cause only mild enteritis because of their very low virulence. This article reviews recent progress in FCoV research with regard to FCoV etiological characteristics; epidemiology; clinical symptoms and pathological changes; pathogenesis; and current diagnosis, prevention and treatment methods. It is hoped that this review will provide a reference for further research on FCoV and other coronaviruses.

Clinical Follow-Up and Postmortem Findings in a Cat That Was Cured of Feline Infectious Peritonitis with an Oral Antiviral Drug Containing GS-441524

This is the first report on a clinical follow-up and postmortem examination of a cat that had been cured of feline infectious peritonitis (FIP) with ocular manifestation by successful treatment with an oral multicomponent drug containing GS-441524. The cat was 6 months old when clinical signs (recurrent fever, lethargy, lack of appetite, and fulminant anterior uveitis) appeared. FIP was diagnosed by ocular tissue immunohistochemistry after enucleation of the affected eye. The cat was a participant in a FIP treatment study, which was published recently. However, 240 days after leaving the clinic healthy, and 164 days after the end of the 84 days of treatment, the cured cat died in a road traffic accident. Upon full postmortem examination, including histopathology and immunohistochemistry, there were no residual FIP lesions observed apart from a generalized lymphadenopathy due to massive lymphoid hyperplasia. Neither feline coronavirus (FCoV) RNA nor FCoV antigen were identified by quantitative reverse transcription polymerase chain reaction (RT-qPCR) and immunohistochemistry, respectively, in any tissues or body fluids, including feces. These results prove that oral treatment with GS-441524 leads to the cure of FIP-associated changes and the elimination of FCoV from all tissues.

Detection of Feline Coronavirus Variants in Cats without Feline Infectious Peritonitis

(1) Background: This study aimed to detect feline coronavirus (FCoV) and characterize spike (S) gene mutation profiles in cats suffering from diseases other than feline infectious peritonitis (FIP) using commercial real-time reverse transcription polymerase chain reaction (RT-qPCR) and reevaluating results by sequencing. (2) Methods: In 87 cats in which FIP was excluded by histopathology and immunohistochemistry, FCoV 7b gene and S gene mutation RT-qPCR was performed prospectively on incisional biopsies and fine-needle aspirates of different organs, body fluids, and feces. Samples positive for S gene mutations or mixed FCoV underwent sequencing. (3) Results: In 21/87 cats, FCoV RNA was detectable. S gene mutations were detected by commercial RT-qPCR (and a diagnostic algorithm that was used at the time of sample submission) in at least one sample in 14/21 cats (66.7%), with only mutated FCoV in 2/21, only mixed in 1/21, and different results in 11/21 cats; in the remaining 7/21 cats, RNA load was too low to differentiate. However, sequencing of 8 tissue samples and 8 fecal samples of 9 cats did not confirm mutated FCoV in any of the FCoV RNA-positive cats without FIP. (4) Conclusions: Sequencing results did not confirm results of the commercial S gene mutation RT-qPCR.