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In November 2020, a volunteer group reported an outbreak of an infectious disease with a high fatality rate and flu-like symptoms among stray cats in Aoshima, a remote island in Ehime, Japan. Nine adult cats with severe symptoms were hospitalized. Feline calicivirus (FCV) was isolated from pharyngeal swabs of six hospitalized cats. An outbreak of virulent systemic FCV (VS-FCV) infection was initially suspected because of obvious flu-like symptoms in adult cats; however, no symptoms typically associated with VS-FCV, such as skin ulcers on the limbs, edema, or viremia, were observed. Notably, two of the hospitalized cats that showed severe disease had diarrhea and anemia, and died or had a prolonged illness. These cases reveal atypical symptoms of FCV infection that have not been previously reported. We further isolated typical strains from western Japan (Osaka, Kumamoto, and Ehime) and analyzed the viral genes along with virulent strains from Aoshima. Phylogenetic analysis showed that the Aoshima strain formed a new lineage distinct from known FCVs. The Aoshima strains isolated in the initial outbreak before December 5, 2020, and those isolated after the end of the outbreak, which are suspected pathogenic and typical non-pathogenic strains, respectively, were located in the same cluster and shown to be very similar in sequence. The virulent Aoshima strain, which causes atypical FCV infections in cats, may have been derived by acquiring several mutations from a typical strain that chronically infects cats on a remote island., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 The Author(s). Published by Elsevier B.V. All rights reserved.)

Feline calicivirus (FCV) causes upper respiratory tract diseases in cats and has highly variable antigenicity for neutralization of each strain. Neutralizing epitopes of FCV are currently found in the hypervariable region (HVR) in the P2 domain of the major capsid protein VP1. Due to its unique ability to neutralize various FCV strains, 1D7 is a monoclonal antibody that may recognize a novel neutralizing epitope. While other neutralizing epitopes were characterized by producing neutralization-resistant variants, only 1D7-resistant variants could not be obtained, and its epitope has not been identified in the previous studies. In this study, we successfully generated these variants by multiple passaging of the FCV F4 strain in the presence of 1D7 and discovered that several amino acid substitutions (K638N, R662G, and T666I in the P1 domain of VP1) are involved in the decreased binding of 1D7. These substitution sites are also highly conserved among FCV strains compared with the substitution sites of other neutralization-resistant variants found in the HVR. Our results indicate that amino acid substitutions in the P1 domain, which are not responsible for direct interaction with the FCV receptor, are associated with neutralization escape. Since FCV can be conveniently cultured in vitro and the receptor required for infection is known, a detailed analysis of the 1D7 epitope could shed more light on the neutralization mechanism of the epitopes of viruses belonging to the Caliciviridae., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Calicivirus infection in patients and animals is associated with the production of multiple inflammatory cytokines, including tumor necrosis factor α (TNF-α). Here we studied the feline calicivirus (FCV) non-structural proteins and found that the FCV protease was a key factor for TNF-α gene expression in cultured cells. The expression of the TNF-α gene in cells expressing FCV, human norovirus, and rabbit hemorrhagic disease virus protease was compared, revealing that the induction of TNF-α could be a common phenomenon during the infection by the viruses in the Caliciviridae. The level of TNF-α mRNA in the cells expressing mutant proteases that lacked the active site was measured. These data indicate that the protease activity is crucial for TNF-α expression. These findings provide new insight into the induction of inflammation during calicivirus infection., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Bats are now known as the source of several diseases in humans, but few studies regarding immune responses and factors associated with bats have so far been reported. In this study, we focused on STAT1, one of the critical components in interferon (IFN)-signaling and antiviral activity, which is often targeted by viral proteins to reduce antiviral activity and increase viral replication. We found that Rousettus aegyptiacus STAT1 (bat STAT1) is phosphorylatable and translocates to the nucleus when stimulated with human IFN-alpha (hIFN-alpha). Furthermore, phosphorylation of bat STAT1 and inhibition of nuclear translocation was observed in IFN-stimulated cells infected with the HEP-Flury strain of rabies virus, in the same manner as in other mammals. Additionally, quantitative real-time RT-PCR revealed that bat STAT1 mRNA was highly expressed in the liver, while low in muscle and spleen., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Infection with bovine viral diarrhea virus (BVDV) causes different effects depending on its biotype in vitro; cytopathogenic (cp) strains induce apoptosis, type I interferon (IFN), and various stress-mediated responses, whereas non-cytopathogenic (ncp) strains do not. However, comprehensive transcriptional profiles of the cells infected with BVDV are still unknown. Here we performed microarray analysis of BVDV-infected MDBK epithelial cells and bovine fetal muscle (BFM) fibroblast cells. Infection of both cell types with cp BVDV, but not ncp BVDV, stimulated marked up-regulation of numerous genes belonging to diverse functional classes. However, the pattern of gene expression detected in both cell types was highly distinct from each other. Notably, upon cp BVDV infection, BFM cells exhibited marked induction of IFN-stimulated genes (ISGs), whereas MDBK cells characteristically up-regulated endoplasmic reticulum stress-inducible genes, such as tribbles homolog 3 (TRB3), CHOP and asparagine synthase, and showed much weaker induction of ISGs than BFM cells. This study highlights unexpected diversity in the response of different cell types to BVDV infection.

Background: Emerging infectious diseases pose a significant risk to public health. Methods for rapid detection of pathogens are needed to effectively treat these diseases. Recently, we developed new methods for the rapid determination of viral RNA sequences, RDV ver1.0 and ver2.0. We demonstrated that these methods were able to simultaneously detect cDNA fragments of many different viruses without using sequence specific primers. However, some species of viruses, including the Yokose virus (YOKV), a flavivirus, could not be detected using the conventional procedures., Objective: The RDV method was further modified to reduce the candidate PCR primer sets., Study Design: Primer sets were reduced to 256 sets in the improved RDV ver3.0, and theoretically, all viral cDNA fragments ligated by two kinds of adaptors after digestion by two restriction enzymes could be amplified in the PCR step for direct sequencing., Results: We succeeded in obtaining 118 YOKV cDNA fragments of the 141 sequence fragments. The cDNA fragments covered diverse range of viral genome., Conclusion: We were able to reduce the combinations of PCR primer sets used in the RDV method. This RDV method ver3.0 has a potential to detect viral cDNA fragments of both known and unknown RNA viruses rapidly and conveniently.

To know the genetic diversities and phylogenetic relationship among feline foamy virus (FeFV) isolates from domestic cats (Felis catus) and FeFV-related viruses from the Iriomote cats (Felis iriomotensis) and leopard cats (Felis bengalensis) in geographically distinct areas, we sequenced a partial gag-pol region of 17 strains and a partial env region of nine strains, and the U3 region of long terminal repeat of three strains of the viruses. FeFV-related viruses from the feral cats were quite similar to the FeFV from domestic cats in the sequenced regions. In the partial gag region, the identities of nucleotide sequences among the isolates were from 94 to 99%. In the partial env gene, the isolates were divided into two distinct genotypes (F17- and FUV-types) as reported by Winkler et al. (Virology 247 (1999) 144-151). More than 94% nucleotide identities were observed in the env region within a particular env genotype and about 75% nucleotide identities were noted between the two genotypes.

We constructed a recombinant baculovirus expressing feline herpesvirus type I (FHV-1) gD in insect cells (Sf9 cells). The expressed product was identified as FHV-1 gD by a panel of monoclonal antibodies specific for the FHV-1 gD, and had an apparent molecular mass of approximately 49 kDa, which was less than that of the authentic FHV-1 gD. When the FHV-1 gD protein were expressed in Sf9 cells and CRFK cells in the presence of tunicamycin, the FHV-1 gD exhibited a molecular mass of 41 kDa. It was shown that the gD protein was transported to the surface of recombinant virus-infected Sf9 cells when examined by membrane-immunofluorescence analysis, and that the gD expressed on the surface of Sf9 cells adsorbed feline erythrocytes. Mice inoculated with a lysate of Sf9 cells expressing FHV-1 gD induced antibodies with virus-neutralizing and hemagglutination-inhibition activities. Therefore, the expressed gD appears to be biologically authentic. These data suggested that recombinant FHV-1 gD produced in Sf9 cells may be a useful immunogen as a feline vaccine.

In this study, an entire open reading frame encoding the capsid protein of feline calicivirus (FCV) F4 strain was inserted into the deletion locus (SmaI site) of the thymidine kinase (TK) deficient mutant (C7301dlTK) of feline herpesvirus type 1 (FHV-1) and the resulting recombinant virus was designated as C7301dlTK-Cap. Expression of the FCV antigens by C7301dlTK-Cap was confirmed by indirect immunofluorescence assay and immunoblot analysis. To assess whether the recombinant virus can induce virus neutralizing (VN) antibody against FCV in the natural host, three cats were inoculated intranasally and orally with C7301dlTK-Cap (two cats) or C7301dlTK (one cat). As a result, sera collected from cats inoculated with the C7301dlTK-Cap possessed VN antibody against FCV. This recombinant virus is expected as a new polyvalent recombinant vaccine against FHV-1 and FCV infections.

A recombinant baculovirus, the genome of which contains DNA encoding Marek's disease virus serotype 1 (MDV1) homolog of glycoprotein D (gD) of herpes simplex virus under the polyhedrin promoter was constructed and designated rAcMDV1gD. Five monoclonal antibodies (MAbs) which recognize the MDV1 homolog of gD (MDV1 gD) in Spodoptera frugiperda cells infected with rAcMDV1gD were prepared. The MAbs reacted with proteins ranging from 52 to 49 kDa in rAcMDV1gD-infected cell lysates by immunoblot analysis. These molecular weights were coincident with molecular weights predicted from the open reading frame of MDV1 gD. By ELISA additivity test, the 5 MAbs were divided into 3 groups which seemed to recognize 3 different epitopes. In addition, all of the 5 MAbs were reactive with chick embryo fibroblasts (CEFs) expressing MDV1 gD. The MAbs are considered to be useful to study the role of MDV1 gD in MDV1 infection.

We constructed the recombinant baculovirus expressing the gene of non-pathogenic Marek's disease virus (MDV) serotype 2 (MDV2) which encodes a polypeptide with partial homology to MDV serotype 1 (MDV1) pp38, an antigen associated with transformed cells. The recombinant MDV2 protein was detected as a band of 32 kDa in immunoblot analysis with MDV2-infected chicken serum. Mouse serum against insect Spodoptera frugiperda cells infected with the recombinant baculovirus immunoprecipitated a 38 kDa molecule from the lysate of MDV2-infected chicken embryo fibroblasts (CEFs) but did not immunoprecipitate the MDV1 pp38 from the lysate of MDV1-infected CEFs. This result indicates that the recombinant MDV2 protein has no epitopes shared with the MDV1 pp38.

An entire open reading frame in a cDNA encoding the capsid protein gene of feline calicivirus (FCV) was subcloned into a mammalian expression vector. After transfection of the constructed plasmid (pMCV-II) into COS-7 cells, the expressed protein was detected by indirect immunofluorescence assay (IFA) using a panel of monoclonal antibodies (MAbs) to the capsid protein of FCV. All of the MAbs reacted with the transfected COS-7 cells in IFA. The 76 kDa capsid precursor protein was demonstrated in an immunoblot analysis, indicating that the translated precursor protein was not processed into the matured capsid protein in this expression system. Two in-frame deleted and a frameshift mutated cDNAs were generated by using restriction sites within the capsid protein coding sequence in pMCV-II to analyze the antigenic sites of the protein. The results of IFA using the MAbs and COS-7 cells transfected with the deleted or mutated cDNAs suggested that three neutralizing epitopes had a conformational nature and that the other four linear epitopes were related to 74 amino acid residues between positions 381 and 454 in the protein, in which high variation was known to be present among three strains of FCV.