Attenuation of the hog cholera virus by continuous cell-virus propagation

Summary A titration method for hog cholera viruses (HCV) of low virulence (strain LOM) has been described. The method, designated the INC-method, is based upon interference between the preinoculated strain LOM and the postinoculated Newcastle disease virus in swine testicle cell cultures.The INC-method has been shown to be an accurate method for the titration of HCV and neutralizing antibodies and proved to be as sensitive as the swine inoculation test.     

Replicate titrations of a vaccinia virus batch by two different titration methods

Summary Two different titration methods were compared. The calculations were based on results of a number of virus titrations of one single batch of smallpox vaccine. It was found that the final titre expressed as pock forming units in eggs was very much influenced from the choice of virus dilution in the inoculation dose. The virus titer is estimated in a more reliable way by end point titration in tissue culture.     

Tissue culture end-point titrations as a routine potency test for smallpox vaccine

Summary A routine procedure for potency testing of smallpox vaccine in monkey tissue cultures (standing tubes) is described. With ten tubes per tenfold dilution of virus the standard deviation of single titers was about 0.2 log unit. Variation of the susceptibility of different cell lots was generally small and did not justify correction with standard titers. The correlation between tissue culture titers and public primary vaccination results was satisfactory (correlation coefficient 0.8), though the latter probably incorporated large sampling errors.It is proposed that tissue culture titration should be officially accepted as an independent potency test for smallpox vaccine.     

Establishment and characterization of two new pig cell lines for use in virological diagnostic laboratories

Two pig cell lines derived from kidney and trachea tissues and referred to as newborn swine kidney (NSK) and newborn pig trachea (NPTr) were established following serial culture of primary cells. They were characterized by an epithelial-like morphology, high capacity to replicate and stability of the cell monolayer for several days after seeding. Their modal chromosome number was modified in comparison to that of primary swine cells and they both displayed a transforming potential in vitro and displayed oncogenicity in nude mice. Infection with pig endogenous retroviruses was detected. Almost all the swine viruses tested, i.e., pseudorabies virus, pig parvovirus, hog cholera virus, transmissible gastroenteritis virus of swine, encephalomyocarditis virus, swine vesicular disease virus and the enteroviruses, except pig reproductive respiratory syndrome virus, were capable of replicating in the new cell lines with titres similar to the ones detected in the reference culture systems. Furthermore, all the selected influenza virus sub-types isolated from human, swine and avian species replicated with cytopathic effect in NSK and NPTr cells, whereas, of all the equine influenza viruses tested only the Miami and Suffolk sub-types replicated.     

Human MxA protein inhibits the replication of classical swine fever virus

Classical swine fever virus (CSFV) has a spherical enveloped particle with a single stranded RNA genome, the virus belonging to a pestivirus of the family Flaviviridae is the causative agent of an acute contagious disease classical swine fever (CSF). The interferon-induced MxA protein has been widely shown to inhibit the life cycle of certain RNA viruses as members of the Bunyaviridae family and others. Interestingly, it has been reported that expression of MxA in infected cells was blocked by CSFV and whether MxA has an inhibitory effect against CSFV remains unknown to date until present. Here, we report that CSFV replicated poorly in cells stably transfected with human MxA. The proliferation of progeny virus in both PK-15 cell lines and swine fetal fibroblasts (PEF) continuously expressing MxA was shown significantly inhibited as measured by virus titration, indirect immune fluorescence assay and real-time PCR.     

Isolation and cultivation of a swine rotavirus

A swine rotavirus capable of inducing the cytopathic effect was isolated in a roller culture of Macaca rhesus kidney cells (line MA-104) after two preliminary passages in gnotobiotic piglets and colostrum-free piglets, and the isolate was designated strain K. For virus isolation, fecal specimens were treated with trypsin, and besides, trypsin was added into the maintenance medium. After 20 passages in MA-104 cell culture the swine rotavirus was adapted to pig embryo kidney cell cultures (SPEV line) in which the maximum virus accumulation, 8.0 log TCD50/ml, was achieved within 24 hours after inoculation. The virus accumulation was most marked in the presence of 10 micrograms/ml trypsin in the maintenance medium. In the roller culture, the virus multiplied to a much higher titre (approximately 100-fold) than in the stationary culture. In the course of passages the virus was shown to lose its pathogenic properties. A scheme of swine rotavirus virion structure is suggested on the basis of ultramicroscopic studies.     

Complete genome comparison of porcine reproductive and respiratory syndrome virus parental and attenuated strains

Two full-length porcine reproductive and respiratory syndrome virus (PRRSV) genomes, strain VR-2332 and its cell culture passaged descendent RespPRRS vaccine strain, were compared and analyzed in order to identify possible sites of attenuation. Of the 44 nucleotide changes, 13 resulted in conservative changes and 18 produced non-conservative changes. The results suggest that key amino acids in ORF1 may contribute to the phenotype of RespPRRS, which includes increased growth rate on MA-104 cells and decreased virulence in swine. The results provide a genetic basis for future manipulation of a PRRSV reverse genetics system.     

Growth of Russian spring summer encephalitis (RSSE) virus in monolayer cell cultures of porcine kidney,bovine emhryo kidney and chicken embryo

Summary The Parker strain of Russian spring-summer encephalitis virus was maintained by serial passage in cell cultures of pig kidney, bovine embryo kidney and chick embryo. In pig kidney cell culture the virus proliferated and produced cytopathic changes. Bovine embryo kidney cell culture supported the proliferation of the virus but no cytopathic effect was produced. In chick embryo cell culture cytopathic changes, which were not shown in the early stages of passage, appeared after several passages. The virus adapted to this host system produced more acids in this culture under certain conditions. The virus interfered with Newcastle disease virus in cell cultures of swine kidney and bovine embryo kidney but not in chick embryo cell culture. The cytopathogenesis in chick embryo or pig kidney cell culture, the interference phenomenon with Newcastle disease virus in bovine embryo or pig kidney cell culture and the pH change in chick embryo cell culture could be employed as criteria for detecting and measuring the virus and its neutralizing antibody.     

Differential polymerase chain reaction for detection of wild-type and a vaccine strain of Aujeszky's disease (pseudorabies) virus.

A polymerase chain reaction (PCR) strategy for differentiating between a vaccine mutant strain and wild-type (WT) strains of Aujesky's disease (pseudorabies) virus (ADV) was evaluated. With this approach, a single virus or a concurrent WT and vaccine virus infection could be distinguished by targeting the genomic alteration within the vaccine strain. PCR primers were designed for a recombinant vaccine virus that has almost all of the WT gX gene replaced by the lacZ gene. One primer, corresponding to a conserved sequence upstream of the altered region, was selected for common use. The differentiating primers were chosen from the unique WT gX and vaccine lacZ gene sequences. The sensitivity of the differential PCR was analyzed using extracted viral DNA and in vitro infected cell lysates. Approximately 10 and between 10 to 100 molecules of WT and vaccine viral DNAs, respectively, could be detected, regardless of the presence or absence of uninfected cell lysates. Detection of viral DNA from in vitro infected cell cultures approximated this level of sensitivity. The specificity of the amplifications was verified by restriction endonuclease analysis and Southern hybridization. Although the vaccine primer pair target was amplified to a lesser degree as compared to the WT primer pair product, utility of the differential PCR was demonstrated using trigeminal nerve ganglia from swine infected with vaccine virus and WT virus. Both viral targets were detected only by their specific primer pair, in either the single or dual infection.     

Synthesis and immunochemical properties of the recombinant major surface glycoprotein E2 of the classical swine fever virus

Recombinant E2 protein from vaccine strain of classical swine fever virus (CSFV) and from SCFV virulent strain Shimen was synthesized in SF-21 and High-Five cell culture with baculovirus as the expressing vector. For secretion, hydrophobic C-terminal transmembrane domain was removed and N-terminal signal polypeptide of 38 amino acids was added. Maximum accumulation of recombinant products in SF-21 cells was observed after 48 h and in medium 96 h after infection with recombinant baculovirus. In High-Five cells and in culture medium the maximum accumulation of E2 was observed after 96 h. The level of E2 expression is 5-10 micrograms/106 cells. The products of expression were purified by affinity chromatography and their specificity confirmed in immunochemical tests with a series of reference monoclonal antibodies. The product can be used for detecting antibodies to SCFV by competitive enzyme immunoassay.     

Restriction endonuclease analysis of the pseudorabies (Aujeszky's disease) virus before and after serial passagein vivo andin vitro

Summary The deoxyribonucleic acid (DNA) of pseudorabies virus (PRV) was examined by restriction endonuclease analysis before and after various treatments: namely 1. plaque purification of stock virus, 2. serial passage of virus in cell culture at high (H) and low (L) multiplicity of infection (MOI), and 3. serial passage of virus in swine. The objective of the study was to determine if such treatments would either select or induce virus populations with a different predominant number or location of enzyme cleavage sites.Heterogeneity of the DNA of stock virus was revealed by differences among restriction patterns of 10 plaque-purified populations. All of these populations were then relatively stable through an additional 9 plaque purifications and passages in cell culture. Without plaque purification, heterogeneity was not evident. The predominant restriction pattern of stock virus appeared unaltered by 10 serial passages in cell culture at either HMOI or LMOI, except for the appearance in the HMOI series of several minor bands. Conversely, 10 serial passages of stock virus in swine resulted in either selection or induced changes or both. Most differences were slightly altered migration rates of relatively small (5 Kbp) fragments. However, after 10 passages in swine, there were also changes in the migration rates of 2 large fragments (>10 Kbp) of the viral genome.With 4 Figures     

Japanese encephalitis DNA vaccine candidates expressing premembrane and envelope genes induce virus-specific memory B cells and long-lasting antibodies in swine

Swine are an important amplifier of Japanese encephalitis (JE) virus in the paradomestic environment. In this study, two JE DNA vaccine candidates were evaluated for immunogenicity in swine. Both vaccine plasmids encode a cassette consisting of the signal of premembrane (prM), prM, and envelope (E) coding regions of JE virus. One plasmid, designated pcJEME, is based on a commercial vector (pcDNA3), whereas the other plasmid, designated pNJEME, is based on a vector (pNGVL4a) designed to address some of the safety concerns of DNA vaccine use. No differences were detected in the immunogenicity of these two plasmids in mice or swine. Swine immunized with the DNA vaccines at a dose of 100 to 450 microgram at an interval of 3 weeks developed neutralizing and hemagglutination-inhibitory (HAI) antibody titers of 1:40 to 1:160 at 1 week after the second immunization. However, swine administered two doses of a commercial JE vaccine (formalin-inactivated virus preparation; JEVAX-A) developed low (1:10) or undetectable antibody responses after their boost. Interestingly, serum antibody titers elicited by DNA vaccines in swine were higher than those detected in mice. Eight days after boosting with viral antigen (JEVAX-A) to detect an anamnestic response, swine immunized two times with the DNA vaccine showed a >100-fold elevation in HAI titer, indicating a strong recall of antibody response. Swine maintained detectable levels of HAI antibody for at least 245 days after two immunizations with a DNA vaccine. These results indicate that these DNA vaccines are able to induce virus-specific memory B cells and long-lasting antibodies in swine, which were of higher levels than those obtained with a commercial formalin-inactivated JE vaccine.     

New generation of cell culture assay for smallpox vaccine potency

The potency of smallpox vaccines produced in the 1970s was tested by titration onto chorioallantoic membranes of fertilized hen eggs (CAM assay). The potency specification commonly approved for these vaccines was a titer above 10(8) pock-forming units per milliliter. We developed and validated a cell culture titration assay to have a more reliable potency test. The cell titration assay and the CAM assay were tested in parallel on 34 first-generation smallpox vaccine lots. These allowed us to demonstrate that a correlation does exist between the two titration techniques and to determine a new in-house specification for the cell titration method. This in vitro potency assay will allow us to test first-generation smallpox vaccines produced on the skin of living animals but will also give a hint of the potency specification that should be assigned for new generations of cell-derived smallpox vaccines.     

Chimeric influenza-virus-like particles containing the porcine reproductive and respiratory syndrome virus GP5 protein and the influenza virus HA and M1 proteins

Both porcine reproductive and respiratory syndrome and swine influenza are acute, highly contagious swine diseases. These diseases pose severe threats for the swine industry and cause heavy economic losses worldwide. In this study, we have developed a chimeric virus-like particle (VLP) vaccine candidate for porcine reproductive and respiratory syndrome virus (PRRSV) and H3N2 influenza virus and investigated its immunogenicity in mice. The HA and M1 proteins from the H3N2 influenza virus and the PRRSV GP5 protein fused to the cytoplasmic and transmembrane domains of the NA protein were both incorporated into the chimeric VLPs. Analysis of the immune responses showed that the chimeric VLPs elicited serum antibodies specific for both PRRSV GP5 and the H3N2 HA protein, and they stimulated cellular immune responses compared to the responses to equivalent amounts of inactivated viruses. Taken together, the results suggested that the chimeric VLP vaccine represents a potential strategy for the development of a safe and effective vaccine to control PRRSV and H3N2 influenza virus.     

Lithium chloride inhibits early stages of foot‐and‐mouth disease virus (FMDV) replication in vitro

Foot‐and‐mouth disease virus (FMDV) causes an economically important and highly contagious disease of cloven‐hoofed animals such as cattle, swine, and sheep. FMD vaccine is the traditional way to protect against the disease, which can greatly reduce its occurrence. However, the use of FMD vaccines to protect early infection is limited. Therefore, the alternative strategy of applying antiviral agents is required to control the spread of FMDV in outbreak situations. As previously reported, LiCl has obviously inhibition effects on a variety of viruses such as transmissible gastroenteritis virus (TGEV), infectious bronchitis coronavirus (IBV), and pseudorabies herpesvirus and EV‐A71 virus. In this study, our findings were the first to demonstrate that LiCl inhibition of the FMDV replication. In this study, BHK‐21 cell was dose‐dependent with LiCl at various stages of FMDV. Virus titration assay was calculated by the 50% tissue culture infected dose (TCID₅₀) with the Reed and Muench method. The cytotoxicity assay of LiCl was performed by the CCK8 kit. The expression level of viral mRNA was measured by RT‐qPCR. The results revealed LiCl can inhibit FMDV replication, but it cannot affect FMDV attachment stage and entry stage in the course of FMDV life cycle. Further studies confirmed that the LiCl affect the replication stage of FMDV, especially the early stages of FMDV replication. So LiCl has potential as an effective anti‐FMDV drug. Therefore, LiCl may be an effective drug for the control of FMDV. Based on that, the mechanism of the antiviral effect of LiCl on FMDV infection is need to in‐depth research in vivo.

     

Production, characterisation and applications of monoclonal antibodies to two novel porcine bocaviruses from swine in Northern Ireland

The production, preliminary characterisation and applications of monoclonal antibodies (mAbs) against two novel swine bocaviruses isolated in cell culture from swine in Northern Ireland are described. Of the 17 stable final clones produced, four were characterised. All were of the IgG2a isotype and showed no cross-reactivity with either bocavirus strain. Partial neutralisation was observed with PBoV4 mAbs and homologous virus. The two mAbs selected for use in antigen-detecting ELISAs were successful in highlighting those fractions containing infectious virus within sucrose gradients. This is the first report of the production of specific reagents that will prove useful in the study of the biology of these viruses and swine bocavirus-associated diseases.     

Determination of genotoxicity of classical swine fever vaccine in vitro by cytogenetic and comet tests

Chromosome damage in lymphocyte cultures induced by live virus vaccine against classical swine fever (CSF) has been observed in previous studies. In vivo cytogenetic tests were made with several doses of vaccines used in Argentina to control the disease. These studies have shown that genotoxic effects increased with dose. In the present study, two different in vitro assays were performed by recording the frequency of cells with chromosome alterations and by assessing the ability of the vaccine to damage DNA, using the single cell gel microelectrophoretic assay (comet test). Frequencies of cells with chromosomal alterations increased significantly when compared with controls and were dose (microl/ml) dependent: 0 = 1.23, 5 = 2.29, 10 = 5.42 and 20 = 11.71%. In the comet assay the variables measured, tail length (TL) and tail moment (TM), also increased. For control cultures TL was 2.32 microm, whereas with concentrations of 20 and 100 microl/ml TL were 12.47 and 42.3 microm, respectively. TM of control cultures was 0.18, whereas with vaccine concentrations of 20 and 100 microl/ml TM were 5.52 and 24.52, respectively. Comet frequency distributions differed significantly among treatments. These results agree with previous in vivo observations. Regarding CSF pathogeny, our results support a direct effect of CSF vaccinal virus on lymphocyte DNA. Genotoxicity of CSF vaccine was corroborated in vitro at the cytogenetic and molecular levels.     

结晶紫蚀斑法检测重组痘苗病毒艾滋病疫苗病毒滴度方法的建立

目的 建立重组天坛株痘苗病毒(rTV)艾滋病疫苗的结晶紫蚀斑病毒滴度检测方法,为rTV艾滋病疫苗病毒滴度测定提供更稳定的方法.方法 通过对Vero细胞浓度、病毒吸附时间及温度、病变判定时间等方面进行优化,建立rTV艾滋病疫苗病毒滴度的结晶紫蚀斑检测方法,并应用BioSpot Reader进行蚀斑计数及分析,比对仪器蚀斑计数和人工蚀斑计数的相关性;应用血球吸附法、中性红蚀斑、结晶紫蚀斑3种方法,对多批rTV艾滋病疫苗及天坛株痘病毒滴度进行检定,进行3种方法的相关性分析;采用结晶紫蚀斑法重复测定样品,计算变异系数(CV),对方法的精密性进行验证;采用SPSS17.0软件对实验数据进行统计分析.结果 确定Vero细胞浓度为5.0×105 ～9.0×105个/ml时,病毒37℃吸附2h后加入含甲基纤维素的维持液,培养72 h,应用BioSpot Reader进行蚀斑计数,与人工计数的相关系数r=0.985,能客观反映不同大小的病毒蚀斑,降低了人工计数引起的非客观因素误差;经过3种方法对不同批次的rTV艾滋病疫苗及天坛株痘病毒进行病毒滴度检定,结晶紫蚀斑与血吸附法的相关系数r=0.997,结晶紫蚀斑法与中性红蚀斑法相关系数r=0.980 (P＜0.01),具有高度相关性.结论 建立了可用于rTV艾滋病疫苗病毒滴度检测的结晶紫蚀斑方法.     

Promising multiple-epitope recombinant vaccine against foot-and-mouth disease virus type O in swine

In order to develop a completely safe immunogen to replace the traditional inactivated vaccine, a tandem-repeat multiple-epitope recombinant vaccine against foot-and-mouth disease (FMD) virus (FMDV) type O was developed. It contained three copies each of residues 141 to 160 and 200 to 213 of VP1 of the O/China/99 strain of FMDV coupled with a swine immunoglobulin G heavy-chain constant region (scIgG). The data showed that the multiple-epitope recombinant vaccine elicited high titers of anti-FMDV specific antibodies in swine at 30 days postvaccination (dpv) and conferred complete protection against a challenge with 103 50% swine infective doses of the O/China/99 strain. The anti-FMDV specific antibody titers were not significantly different between the multiple-epitope recombinant vaccine and the traditional vaccine (t test, P > 0.05). The number of 50% pig protective doses was 6.47, which is higher than the number recommended by the World Organization for Animal Health. The multiple-epitope recombinant vaccine resulted in a duration of immunity of at least 6 months. We speculate that the multiple-epitope recombinant vaccine is a promising vaccine that may replace the traditional inactivated vaccine for the prevention and control of FMD in swine in the future.     

Surface properties of Chlamydia psittaci.

The S-1 clone of dengue type 2 virus was used for the preparation of a live-attenuated vaccine after passage in DBS-FRhL-2 cell culture. The vaccine virus had a relatively higher replicative capacity at superoptimal temperatures than its precursor virus, S-1, passaged in primary green monkey kidney cells (S-1 PGMK). There was also a tendency for the S-1 vaccine virus to exhibit leakiness at increased temperatures. Another in vitro marker, replication in monkey peripheral blood leukocytes, indicated less host restriction for the S-1 vaccine in comparative assays with S-1 PGMK virus. Mouse virulence appeared to remain stable on passage in DBS-FRhL-2 cells, whereas monkey immunogenicity decreased. Cautious trials of the dengue type 2 S-1 vaccine in humans are indicated.