Development of a real-time RT-PCR assay combined with ethidium monoazide treatment for RNA viruses and its application to detect viral RNA after heat exposure.

A method was developed for discriminating damaged viruses or naked viral RNA from intact viruses by ethidium monoazide (EMA) treatment before RT-PCR. The applied EMA treatment consisted of three steps: (1) EMA dose, (2) exposure to light, and (3) additional purification by spin-column gel filtration. Approximately 4-log reduction in viral RNA concentration was observed by adding a dose of 10 µg/mL-EMA with 300 s of light irradiation. Although residual EMA can be an inhibitor of RT-PCR, its effect was reduced by spin-column gel filtration or a QIAamp® Viral RNA Mini Kit. EMA-RT-PCR was applied to the thermally treated PV1. Results of EMA-RT-PCR were similar to the plaque assay when PV1 was thermally inactivated. Although this is a preliminary study investigating applicability of the EMA-RT-PCR method for RNA viruses, the results suggest that the method is potentially applicable for the selective detection of epidemiologically important enteric viruses in water such as enteroviruses and noroviruses.

Chlorine inactivation of human norovirus, murine norovirus and poliovirus in drinking water.

AIMS: To evaluate the reduction of human norovirus (HuNoV) by chlorine disinfection under typical drinking water treatment conditions. METHODS AND RESULTS: HuNoV, murine norovirus (MNV) and poliovirus type 1 (PV1) were inoculated into treated water before chlorination, collected from a drinking water treatment plant, and bench-scale free chlorine disinfection experiments were performed for two initial free chlorine concentrations, 0.1 and 0.5 mg l(-1). Inactivation of MNV reached more than 4 log(10) after 120 and 0.5 min contact time to chlorine at the initial free chlorine concentrations of 0.1 and 0.5 mg l(-1), respectively. CONCLUSIONS: MNV was inactivated faster than PV1, and there was no significant difference in the viral RNA reduction rate between HuNoV and MNV. The results suggest that appropriate water treatment process with chlorination can manage the risk of HuNoV infection via drinking water supply systems. SIGNIFICANCE AND IMPACT OF THE STUDY: The data obtained in this study would be useful for assessing or managing the risk of HuNoV infections from drinking water exposure.

Enhancement of apoptosis via an extrinsic factor, TNF-alpha, in cells infected with cytopathic bovine viral diarrhea virus.

Isolates of bovine viral diarrhea virus (BVDV) are divided into cytopathic (cp) and noncytopathic (ncp) biotypes according to their effect on cultured cells. Calves persistently infected with ncp BVDV are known to develop lethal mucosal disease (MD) after superinfection by cp BVDV. Although the UV-irradiated supernatant of cp BVDV-infected cells has been reported to have no capacity to induce cell death, we found that it could enhance cell death through apoptosis. Up-regulation of tumor necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) mRNAs was detected specifically in cp BVDV-infected primary cell cultures. Suppression of TNF-alpha via antisense oligonucleotide transfection or incubation with a polyclonal antibody against TNF-alpha resulted in attenuation of apoptosis induced by cp BVDV, suggesting that TNF-alpha participates in apoptosis execution. Although TNF-alpha is one of the iNOS-inducible factors, the iNOS up-regulation was not regulated by TNF-alpha. And iNOS was revealed to serve as anti-apoptotic factor, contrary to our expectation. In addition, the expression level of both TNF-alpha and iNOS mRNAs in the ncp BVDV-infected cells was kept lower than that in the mock-infected cells, suggesting that ncp BVDV reduced or interfered with the factor triggering the expression of both mRNAs. These characteristic mRNA transcriptions would help to explain why BVDV acts differently in cells as well as in vivo, depending on its biotype. To elucidate viral factors inducing TNF-alpha and iNOS may be critical to understand the mechanism of MD development, which closely correlates with cp BVDV-induced apoptosis.

Preparation of monoclonal antibodies against Marek's disease virus serotype 1 glycoprotein D expressed by a recombinant baculovirus.

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.

Expression of Marek's disease virus (MDV) serotype 2 gene which has partial homology with MDV serotype 1 pp38 gene.

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.

Genetic analyses of feline foamy virus isolates from domestic and wild feline species in geographically distinct areas.

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.

Expression and properties of feline herpesvirus type 1 gD (hemagglutinin) by a recombinant baculovirus.

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.

Antigenic analysis of feline calicivirus capsid precursor protein and its deleted polypeptides produced in a mammalian cDNA expression system.

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.

Characterization of several pseudorabies viral strains by virus-neutralization test using monoclonal antibodies.

In the present study, five mouse monoclonal antibodies (MAbs) to the pseudorabies virus (PRV) Yamagata-81 strain were produced. The MAbs were used in cross-neutralization tests and cross-indirect enzyme-linked immunosorbent assay (ELISA) against three PRV viral strains isolated in Argentina and another four obtained from the United States, Japan, France, and Sweden. Four of five MAbs needed the presence of complement to produce or enhance neutralization activity. No differences were observed by ELISA. The MAbs showed different neutralizing activity against PRV strains, suggesting phenotypic heterogeneity among them.

Genetic analysis of a canine calicivirus: evidence for a new clade of animal caliciviruses.

This paper describes the relationship of a canine calicivirus, named No.48, to other human and animal caliciviruses, based on phylogeny of the 3' half of its genome. It was found that No.48 constitutes a unique lineage, most closely related but distinct from feline and San Miguel sea lion caliciviruses.

Two genomic variations in the E1 region of canine adenovirus type 2 strains.

We amplified the E1 region of canine adenovirus type 2 genomes by the polymerase chain reaction (PCR) and analyzed the PCR products by using eight restriction endonucleases. Restriction patterns of the E1 region cleaved with HaeIII and RsaI revealed two genomic variations among the canine adenovirus type 2 strains. Although the clinical significance of two distinct genotypes among the canine adenovirus type 2 strains is currently unknown, these genomic variations are well conserved among different strains in each genotype and suggest that the Japanese field strains, with reference to the E1 region, are different from the non-Japanese strains examined.

Induction of antibodies to canine herpesvirus in mice by immunization with anti-idiotypic antibodies.

Anti-idiotypic antibodies (anti-Id Abs) were produced in rabbits after inoculation with two mouse monoclonal antibodies (mAbs) directed against canine herpesvirus (CHV) glycoproteins (gps). One of the mAbs, 12H11, was directed against an epitope on gp 145/112 of CHV which induced virus neutralizing (VN) antibodies and against a cross-reacting epitope on the gp 143/108 of feline herpes-virus type 1 (FHV-1). The other mAb, 11F7, was directed against epitopes on CHV gp47 which induce VN and hemagglutination-inhibition (HAI) antibodies. Using VN-inhibition and HAI-inhibition assays with CHV and FHV-1, the anti-Id Abs obviously inhibited the activities of autologous mAbs, suggesting that anti-Id Abs mimic the epitopes of CHV gp 145/112 or FHV-1 gp 143/108 and CHV gp47 by binding the anti-combining site of the mAbs. These anti-Id Abs, when injected into mice, elicited specific CHV-neutralizing and HAI antibody responses, and one of them also elicited a specific FHV-1-neutralizing antibody response. These data supported the idea that immunization with anti-Id Ab can induce specific VN antibody response, as has been theorized by other workers.

Carrier-state infection of feline T-lymphoblastoid cells with feline calicivirus.

The susceptibility of feline T lymphocytes to feline calicivirus (FCV) in vitro was investigated using feline T-lymphoblastoid cell lines, namely MYA-1 and FL74 cells. The virus titers of supernatants in FCV-infected MYA-1 and FL74 cell cultures increased rapidly, and FCV antigens were also detected in the FCV-infected cells. There were slight differences in the molecular weights of capsid proteins expressed in FCV-infected MYA-1, FL74 and Crandell feline kidney cells. MYA-1 and FL74 cells were productively and persistently infected with FCV, and FCV antigens were observed in the FCV-infected cells for more than one month. At 3 months post infection, FCV-infected FL74 cells that stopped producing infectious FCV could be reinfected with FCV. However, no cytopathic effects were observed.

Characterization of the most frequently encountered Staphylococcus sp. in cats.

Ninety three staphylococci isolated from clinical specimens from cats were characterized and identified. Because the biochemical characteristics of Staphylococcus felis were very similar to those of Staphylococcus simulans, results were submitted to numerical analysis and DNA homology. Forty-two isolates (45%) were identified as S. felis, and 4 isolates (4%) as S. simulans. The other species identified, in order of their frequency were, 12 Staphylococcus aureus (13%), 9 Staphylococcus intermedius (10), 6 Staphylococcus sciuri (6), 6 Staphylococcus epidermidis (6), 2 Staphylococcus haemolyticus (2), 2 Staphylococcus xylosus (2), 1 Staphylococcus capitis (1), 1 Staphylococcus equorum (1), 1 Staphylococcus gallinarum (1) and 1 Staphylococcus lentus (1).

Characterization of anti-feline CD8 monoclonal antibodies.

We generated three monoclonal antibodies (mAbs) (2D7, 10C7 and 12A3) reactive to the alpha-chain of feline CD8 (fCD8) molecule. Further we showed that reference anti-fCD8 mAbs, FT2, 3.357 and vpg9 recognize the beta-chain, alpha-chain and alphabeta-complex epitope, respectively. Flow cytometric analysis using these mAbs suggested that fCD8alpha(+)beta(-) cells were present in lymphocytes of spleen, but not significantly in those of thymus, lymph nodes and peripheral blood of normal kittens.

Diversity of genomic electropherotypes of naturally occurring equine herpesvirus 1 isolates in Argentina.

The genomes of 10 equine herpesvirus 1 (EHV-1) strains isolated in Argentina from 1979 to 1991, and a Japanese HH1 reference strain were compared by restriction endonuclease analysis. Two restriction enzymes, BamHI and BglII, were used and analysis of the electropherotypes did not show significant differences among isolates obtained from horses with different clinical signs. This suggests that the EHV-1 isolates studied, which circulated in Argentina for more than 10 years, belong to a single genotype.

Detection and classification of infectious bronchitis viruses isolated in Korea by dot-immunoblotting assay using monoclonal antibodies.

Dot-immunoblotting assay (DIA) using five monoclonal antibodies (MAbs) to infectious bronchitis virus (IBV) was used to detect and classify the viruses propagated in embryonated chicken eggs. Using a group-specific MAb 3F5, 10 reference strains and 12 Korean isolates of IBV were successfully detected by DIA, and the lowest virus titer of IBV detected by DIA was approximately less than 10(3.8) mean embryo infective dose/ml. For evaluating the diagnostic efficiency, DIA was compared with the conventional infectious bronchitis (IB) diagnostic method. IBV antigens in allantoic fluid from embryonated eggs inoculated with IB-suspected field samples were specifically detected by DIA within only one or two egg passages, whereas the conventional embryonated egg inoculation method required four to seven egg passages for confirming IBV infection. These results indicated that DIA could significantly reduce time and cost for IB diagnosis. For examining the possibility of classifying IBV by DIA, four strain-specific MAbs, 3A4, 2A3, 6F7, and 2C6, were used. According to the MAb reacting patterns to the IBV antigens, the 10 IBV reference strains were classified into six groups; seven strains belonged to three different groups, and the other three strains each belonged to an individual group. In the case of 12 Korean isolates of IBV, they were classified in six groups. Among the six groups, the MAb reacting patterns of three groups matched those of the IBV reference strains, but the others did not. These data suggest that at least three variant serotypes of IBV exist in Korea.

Characterisation of cross-reactivity of virus neutralising antibodies induced by feline panleukopenia virus and canine parvoviruses.

It was recently reported that canine parvoviruses (CPV) had entered cat populations and induced disease in infected cats, while they had affected only dogs in the past. It is important to determine whether conventional feline panleukopenia virus (FPLV) vaccines protect against recent CPV infections. In this study, the cross-reactivity of virus-neutralising (VN) and haemagglutinin-inhibition (HI) antibodies in cats induced by FPLV and CPV s were examined. Lower cross-reactivities of VN and HI antibodies against each CPV strain were observed in cats experimentally inoculated with FPLV or vaccinated with an inactivated FPLV vaccine. In addition, we revealed the existence of a novel type of FPLV, which reacted weakly with antibodies induced by the conventional FPLV vaccine.

Isolation of a calicivirus antigenically related to feline caliciviruses from feces of a dog with diarrhea.

A CPE-producing agent was recovered in feline cell cultures from feces of a male dog suffering from intermittent watery diarrhea. Antigenic analysis of this isolate, Sapporo/283, was performed using the plaque reduction neutralization and complement fixation assays and it was neutralized by antisera against feline calicivirus (FCV) but not against canine calicivirus (CaCV). Likewise, it showed common CF antigenicity with the other FCV strains included in the experiments. These findings revealed that the isolate was more closely related antigenically to FCV than CaCV, indicating the possibility of interspecies transmission. It was also suggested that the isolate was a respiratory type calicivirus. Epizootiological results suggested, however, that FCV seldom infects dogs under natural condition.

Reactivities of feline calicivirus field isolates with monoclonal antibodies detected by enzyme-linked immunosorbent assay.

Reactivities of feline calicivirus (FCV) field isolates with monoclonal antibodies (MAbs) were examined by enzyme-linked immunosorbent assay (ELISA). The reactivities of the viruses in ELISA were different from our previous results using the neutralization tests (NT). Many isolates were positive in ELISA with MAbs which recognized neutralizing epitope 3B and/or 4. However, most were negative in NT in our previous study. After absorption of two FCV strains with host cells, the non-infectious virus fluid still reacted with MAb, which recognized epitope 3B and/or 4 in ELISA. These results indicated the possibility that neutralizing epitopes are expressed on non-infectious virus particles or exist as proteinaceous molecules in virus fluid.