Genome architecture changes and major gene variations of Andrias davidianus ranavirus (ADRV)

Ranaviruses are emerging pathogens that have led to global impact and public concern. As a rarely endangered species and the largest amphibian in the world, the Chinese giant salamander, Andrias davidianus, has recently undergone outbreaks of epidemic diseases with high mortality. In this study, we isolated and identified a novel ranavirus from the Chinese giant salamanders that exhibited systemic hemorrhage and swelling syndrome with high death rate in China during May 2011 to August 2012. The isolate, designated Andrias davidianus ranavirus (ADRV), not only could induce cytopathic effects in different fish cell lines and yield high viral titers, but also caused severely hemorrhagic lesions and resulted in 100% mortality in experimental infections of salamanders. The complete genome of ADRV was sequenced and compared with other sequenced amphibian ranaviruses. Gene content and phylogenetic analyses revealed that ADRV should belong to an amphibian subgroup in genus Ranavirus, and is more closely related to frog ranaviruses than to other salamander ranaviruses. Homologous gene comparisons show that ADRV contains 99%, 97%, 94%, 93% and 85% homologues in RGV, FV3, CMTV, TFV and ATV genomes respectively. In addition, several variable major genes, such as duplicate US22 family-like genes, viral eukaryotic translation initiation factor 2 alpha gene and novel 75L gene with both motifs of nuclear localization signal (NLS) and nuclear export signal (NES), were predicted to contribute to pathogen virulence and host susceptibility. These findings confirm the etiologic role of ADRV in epidemic diseases of Chinese giant salamanders, and broaden our understanding of evolutionary emergence of ranaviruses.     

Susceptibility of Fish and Turtles to Three Ranaviruses Isolated from Different Ectothermic Vertebrate Classes

Abstract

Ranaviruses have been associated with mortality of lower vertebrates around the world. Frog virus 3 (FV3)-like ranaviruses have been isolated from different ectothermic vertebrate classes; however, few studies have demonstrated whether this pathogen can be transmitted among classes. Using FV3-like ranaviruses isolated from the American bullfrog Lithobates catesbeianus, eastern box turtle Terrapene carolina carolina, and Pallid Sturgeon Scaphirhynchus albus, we tested for the occurrence of interclass transmission (i.e., infection) and host susceptibility (i.e., percent mortality) for five juvenile fish and three juvenile turtle species exposed to each of these isolates. Exposure was administered via water bath (10³ PFU/mL) for 3 d and survival was monitored for 28 d. Florida softshell turtles Apalone ferox experienced no mortality, but 10% and 20% of individuals became infected by the turtle and fish isolate, respectively. Similarly, 5% of Mississippi map turtles Graptemys pseudogeographica kohni were subclinically infected with the turtle isolate at the end of the experiment. Channel Catfish Ictalurus punctatus experienced 5% mortality when exposed to the turtle isolate, while Western Mosquitofish Gambusia affinis experienced 10% mortality when exposed to the turtle and amphibian isolates and 5% mortality when exposed to the fish isolate. Our results demonstrated that interclass transmission of FV3-like ranaviruses is possible. Although substantial mortality did not occur in our experiments, the occurrence of low mortality and subclinical infections suggest that fish and aquatic turtles may function as reservoirs for FV3-like ranaviruses. Additionally, our study is the first to report transmission of FV3-like ranaviruses between fish and chelonians.

Received October 22, 2013; accepted January 8, 2014.     

A New Ranavirus Isolated from Pseudacris clarkii Tadpoles in Playa Wetlands in the Southern High Plains,Texas

Abstract

Mass die-offs of amphibian populations pose a challenging problem for conservation biologists. Ranaviruses often cause systemic infections in amphibians and, in North America, are especially virulent and lethal to larvae and metamorphs. In this paper we describe a novel ranavirus isolate as well as the first recorded occurrence of ranavirus in the southern High Plains of Texas and in associated populations of the spotted chorus frog Pseudacris clarkii. The breeding sites were playas, that is, wetlands that fill via isolated thunderstorms that can occur infrequently; thus, not every playa has water or breeding amphibians annually. We did not detect ranavirus in sympatric anurans, but other reports document ranaviruses in Pseudacris spp. elsewhere. The occurrence of multiple isolates of ranavirus in a number of Pseudacris species suggests that this genus of frogs is highly susceptible to ranaviruses and may experience exceptionally high mortality rates from infection. Thus, the virus may contribute to substantial seasonal population declines and low seasonal recruitment, with negative impacts on populations of breeding adults in successive years.     

Reduction of infectious bursal disease virus replication by shRNAs targeting the VP1 and VP2 genes driven by chicken U6 promoter

Infectious bursal disease virus (IBDV) causes a highly contagious and immunosuppressive disease in young chickens and results in considerable economic losses for the poultry industry. To suppress the replication of IBDV, two short hairpin RNAs (shRNAs) were designed for targeting the VP1 and VP2 genes of IBDV. Recombinant plasmids carrying each shRNA or two shRNAs were constructed based on vector pSilencer2.1-U6 in which the human U6 promoter was replaced with chicken U6 promoter. In chicken embryo fibroblasts, transfection with these shRNA plasmids 24 h before infection with IBDV B87 reduced 50% tissue culture infectious doses (TCID₅₀) from 10^8.75 TCID₅₀/0.1 mL to 10^3.75–10^1.0 TCID₅₀/0.1 mL. In 10-day old specific pathogen-free (SPF) chicken embryos, incubation with a mixture of IBDV B87 and a shRNA plasmid via the allantoic cavity resulted in 100% mortality and high IBDV virus titer in the control group but 25–0% mortality and near normal embryo development in the specific shRNA groups; additionally, IBDV VP1 and VP2 mRNA levels were reduced by 72–95% in the shRNA groups as compared with the control groups. When challenged with a virulent strain IBDV GX8/99, 14-day-old chickens pre-treated with the single shRNA plasmids or the dual shRNA plasmid showed approximately 70% or 90% survival at 5 days post-challenge while those pre-treated with control plasmid or saline had less than 5% survival. The current study suggests that two IBDV shRNAs expressed by a plasmid under chicken U6 promoter could effectively and synergistically reduce IBDV replication in vitro and in vivo.     

Minimum intravenous infectious dose of ovine progressive pneumonia virus (OPPV)

The minimum intravenous infectious dose for ovine progressive pneumonia virus (OPPV) WLC1 was determined using twenty-four 6 month-old lambs. Twelve groups of two 6 month-old lambs were inoculated intravenously (i.v.) with tissue culture fluid containing ovine progressive pneumonia virus (OPPV) WLC1 titers ranging from 10^7.6 TCID₅₀/lamb down to 10^−3.4 TCID₅₀/lamb and were monitored for seroconversion using the OPPV agar gel immunodiffusion assay (AGID). Fifteen of the 16 lambs given equal or greater than 10^0.6 TCID₅₀ seroconverted, and virus could be isolated from peripheral blood leukocytes in 13 out of the 15 of these lambs. None of the eight lambs receiving less than 10^0.6 TCID₅₀ seroconverted during the 12 months. The results of this study indicated that 10^0.6 or 4 TCID₅₀/lamb given i.v. was capable of establishing infection.     

无血清全悬浮PK15细胞培养猪圆环病毒2型的研究

为改进猪圆环病毒2型的培养工艺,驯化了一株可无血清培养的全悬浮PK15细胞用于培养猪圆环病毒2型,并对病毒的敏感性、接毒时间、接毒量、收获方法进行了试验.结果表明,用该细胞培养猪圆环病毒2型,如果采用批次收获,接毒时细胞密度为0.5×106/mL,接毒量为0.1 MOI,接毒72 h后收毒,病毒滴度能达到106.4 T...     

Characterization of the systemic disease and ocular signs induced by experimental infection with Chlamydia psittaci in cats

In addition to the commonly reported ocular signs, Chlamydia psittaci infection of kittens resulted in fever, lethargy, lameness and reduction in weight gain following ocular instillation of virulent organisms. The appearance of these systemic signs was late with respect to the appearance of ocular symptoms and occurred simultaneously with increasing levels of chlamydia-specific IgG. Measurement of acute phase reactants and IL-6 in plasma indicated that both became elevated concurrent with or slightly after the appearance of fever and remained elevated after the fever began to resolve. Preliminary data also indicated that infectious C. psittaci was present in the blood stream during this time period. The results of ocular instillation of three different levels of C. psittaci (10^3.8, 10^2.8 and 10^1.5 TCID₅₀) indicated that the frequency of infection and the severity of ocular signs were diminished in the group receiving the lowest dose. However, the magnitude of systemic disease was similar in all animals which exhibited clinical signs, irrespective of the dose administered. The immune response to infection included elementary body (EB)-specific lymphocyte proliferation as well as the development of EB-specific IgG and IgM antibodies. The predominant antibody response was to a 45 kDa protein, the major outer membrane protein (MOMP), lipopolysaccharide (LPS), a 58 kDa doublet and 32 and 16–19 kDa proteins.     

A Comparison of Three Techniques for Detecting Bovine Herpesvirus Type 1 (BHV-1) in Naturally and Experimentally Contaminated Bovine Semen

Contents: Immune electron microscopy, hybridization (Sandwich, Southern-blot and dot-blot hybridization) as well as two cell culture inoculation techniques to detect bovine herpesvirus 1 (BHV-1) in naturally and artificially contamined bovine semen were compared. Immune electron microscopy was not a suitable method because of its low limit of detection. Dot-blot hybridization, as the most sensitive hybridization technique, could detect 150 pg BHV-1 DNA/semen straw (～ 10⁶TCID₅₀/ 500 μl semen). Best results were obtained by using cell culture techniques. With the first technique embryonic bovine lung cells (EBLC) on microtiterplates were inoculated with an ultracentrifuged pellet of seminal plasma (pelleting method). The second procedure comprised a dilution of 250 μl (1/2 content of a straw) in 6,25 ml cell culture medium which were overlayed on a confluent layer of EBLC in a 25 cm² flask. After an incubation of 4 hours at 37°C the medium was decanted and replaced by 6,5 ml fresh medium (dilution method). With both tissue culture methods as little as 5 TCID₅₀ of BHV-1 in 500 μl of artificially contaminated semen were detectable. However the dilution method was better suited than the pelleting method because toxic effects to cells were less pronounced. It was even possible to detect BHV-1 in naturally contaminated semen samples where all other methods failed. The DNA of virus isolates from semen showed three different restriction patterns. Inhalt: Vergleich dreier Methoden zum Nachweis von bovinem Herpesvirus Typ 1 (BHV-1) in natürlich und experimentell kontaminiertem Rindersamen Die Immunelektronenmikroskopie, die Hybridisation (Sandwich-, Southern-Blot- und die Dot-Blot Hybridisation) sowie zwei Zellkultur-Inokulationstechniken wurden zum Nachweis von bovinem Herpesvirus Typ-1 (BHV-1) in natürlich und künstlich kontaminiertem Stierensamen verglichen. Die Immunelektronenmikroskopie erwies sich dabei als zu wenig empfindliche Methode. Die Dot-Blot Hybridisation war die beste der Hybridbationsmethoden. Es lieβen sich damit bis zu 150 pg BHV-1 DNA/Paillette (～ 10⁶ TCID ₅₀ /500 μl Samen) nachweisen. Am besten eigneten sich Zellkulturmethoden. Eine erste Methode bestand darin, embyonale bovine Lungenzellen in Microtiterplatten mit einem Ultrazentrifugensediment des Samenplasmas zu inokulieren (pelleting method). In einem zweiten Verfahren wurde 1/2 Inhalt einer Pailette (250 μl) in 6,25 ml Zellkulturmedium verdünnt und damit ein Zellrasen von embyonalen bovinen Lungenzellen überschichtet. Nach 4 h bei 37°C wurde das Medium abgegossen und durch 6,5 ml neues Medium ersetzt (Verdünnungsmethode). Mit beiden Methoden lieβen sich 5 TCID₅₀ BHV-1 in 500 μl Rünstlich kontaminiertem Samen nachweisen. Die Verdünnungsmethode war aber besser geeignet, weil der toxische Effekt auf die Zellen geringgradiger war. Mit der Verdünnungsmethode lieβ sich aus Ejakulaten BHV-1 isolieren, auch in Fällen, in denen alle andern Methoden versagten. Die DNA's von Virusisolaten aus Rindersamen wiesen drei verschiedene Restriktionsmuster auf.     

A DNA miniarray system for simultaneous visual detection of porcine circovirus type 1 (PCV1) and 2 (PCV2) in pigs

A miniarray system was developed for the simultaneous detection of porcine circovirus type 1 (PCV1) and type 2 (PCV2) in pigs. The system consists of a polymerase chain reaction (PCR) step to amplify target viral DNA, followed by detection of the amplified DNA using a membrane-anchored probe array and an avidin-alkaline phosphatase (Av-AP) indicator system. The lower limit of detection of PCV using the miniarray was 10^1.9 tissue culture infectious dose 50 (TCID₅₀)/ml and 10^2.08TCID₅₀/ml for PCV1 and PCV2, respectively, and 100 viral copies/μl for both PCV1 and PCV2. We validated the miniarray system using 141 lymph node specimens from pigs with suspected postweaning multisystemic wasting syndrome or porcine dermatitis and nephropathy syndrome. Of the 141 samples evaluated, 55 were identified as positive for PCV by the miniarray. Relative to in situ hybridization, the sensitivity and specificity of the miniarray was 100% and 98.9%, respectively. In contrast to other microarray systems, the miniarray does not require a DNA chip reader, since the results can be determined by visual inspection of colorized spots on a nylon membrane. This system represents an effective alternative method for the differential detection of PCV1 and PCV2 in pigs, as well as the maintenance of PCV-free cell lines and pre-screening of commercial vaccines for possible contamination.     

Replication of neurovirulent equine herpesvirus type 1 (EHV-1) in CD172a+ monocytic cells

Equine herpesvirus type 1 (EHV-1) is responsible for respiratory disorders, abortion and myeloencephalopathy (EHM) in horses. Two pathotypes of EHV-1 strains are circulating in the field: neurovirulent (N) and non-neurovirulent (NN). For both strains, CD172a⁺ monocytic cells are one of the main carrier cells of EHV-1 during primary infection, allowing the virus to invade the horse’s body. Recently, we showed that EHV-1 NN strains showed a restricted and delayed replication in CD172a⁺ cells. Here we characterize the in vitro replication kinetics of two EHV-1 N strains in CD172a⁺ cells and investigate if the replication of these strains is similarly silenced as shown for EHV-1 NN strains. We found that EHV-1 N replication was restricted to 7–8% in CD172a⁺ cells compared to 100% in control RK-13 cells. EHV-1 N replication was not delayed in CD172a⁺ cells but virus production was significant lower (10^3.0 TCID₅₀/10⁵ inoculated cells) than in RK-13 cells (10^8.5 TCID₅₀/10⁵ inoculated cells). Approximately 0.04% of CD172a⁺ cells produced and transmitted infectious EHV-1 to neighbour cells compared to 65% of RK-13 cells. Unlike what we observed for the NN strain, pretreatment of CD172a⁺ cells with histone deacetylases inhibitors (HDACi) did not influence the replication of EHV-1 N strains in these cells. Overall, these results show that the EHV-1 replication of N strains in CD172a⁺ cells differs from that observed for NN strains, which may contribute to their different pathogeneses in vivo.     

Protein display by bovine herpesvirus type 1 glycoprotein B

Glycoprotein B (gB) of bovine herpesvirus 1 (BHV-1), a major component of the viral envelope, is essential for membrane fusion during entry and cell-to-cell spread. It is cleaved in the trans-Golgi network by the proprotein convertase furin. Integration of the open reading frame (ORF) encoding a mutated gB with a second furin cleavage site and mature boIFN-α as intervening peptide between the amino-terminal (NH₂) and carboxy-terminal (COOH) gB subunits yielded recombinant BHV-1/gB2FuIFN-α which, unexpectedly, express gB with an enlarged NH₂-subunit of 90 kDa. Here we show that boIFN-α-specific antibodies bind to the 90 kDa gB subunit and efficiently neutralize BHV-1/gB2FuIN-α infectivity. We also show that inactivated BHV-1/gB2FuIN-α virions induce an antiviral state in cells incubated with UV-inactivated particles. These results demonstrate that the 90 kDa protein is a NH₂-subunit/boIFN-α fusion protein whose boIFN-α domain is biologically active. To verify that BHV-1 gB is suitable for the display of (glyco)proteins on the surface of virions we constructed BHV-1 recombinants expressing within gB the first 273 amino acids of the NH₂-subunit (HA1) of avian influenza haemagglutinin, either flanked by two furin cleavage sites or with only one cleavage site between a gB/NH₂_HA1 fusion protein and the COOH subunit. The resulting recombinant BHV-1/gB2FuHA1 expressed gB from which 55 kDa HA1 was excised and secreted. In contrast, gB from BHV-1/gB_NH₂HA1 infected cells retained HA1 as fusion protein with the NH₂-subunit. Immunoblotting and neutralization analyses revealed that HA1 is incorporated into the envelope BHV-1/gB/NH₂_HA1 particles and exposed to the exterior of virions. Thus, this novel approach enables display of polypeptides and (glyco)proteins of at least 273 amino acids on viral particles which is of particular interest for development of novel diagnostics and vaccines as well as for, e.g. gene therapy applications especially when biologically active ligands need to be presented.     

Comparative Analysis of the Outer Membrane Protein Profiles of Isolates of the Pasteurella multocida (B:2) Associated with Haemorrhagic Septicaemia

Outer membrane proteins (OMP) of P. multocida (serotype B:2) field isolates (n = 6) and a vaccine strain (P-52) were extracted by a sarkosyl method and characterized using SDS-PAGE and immunoblotting. About 20 polypeptide bands were observed in the profile of the vaccine strain with MW ranging from 16 to 90 kDa and, based on band thickness and intensity of staining, three polypeptides of MW 31, 33 and 37 kDa were considered to be the major OMPs. The profiles of the field isolates showed minor differences when compared with that of the vaccine strain. The OMP of 33 kDa was only expressed by the vaccine strain. Four field isolates expressed an OMP of 39 kDa, which did not appear in the profiles of the remaining two field isolates and the P-52 strain. Similarly, an OMP of 25 kDa was exclusively seen in the profile of a single isolate. By immunoblotting studies, using anti-P. multocida (P-52) whole-cell hyperimmune serum raised in rabbits as well as buffalo immune sera, it became evident that the polypeptide of 37 kDa was the most antigenic OMP in the profiles of all the isolates, including the P-52 strain. Other polypeptides were either weakly antigenic or visible in the profile of only a few of the isolates. The study thus identified the major OMP of P. multocida (B:2) and suggested that this highly antigenic 37 kDa OMP has potential for further protective and immunodiagnostic studies.     

The length of BTV-8 viraemia in cattle according to infection doses and diagnostic techniques

Four groups of BTV free Frisian and cross bred calves were used to determine the length of viraemia following infection with different doses of BTV-8 Italian isolate. The first group of five animals was infected with 10 TCID₅₀ of BTV-8, the second group of four animals with 10³ TCID₅₀ and the third group, which also included four animals, was infected with 10⁶ TCID₅₀. A placebo containing uninfected tissue culture medium was given to the four animals of the fourth group. The viraemia was evaluated by real time RT-PCR and virus isolation. In all infected groups, virus isolation was able to detect infectious virus up to 39 days post infection (dpi) while RT-PCR was positive up to 151–157 dpi. Infectious dose did influence neither the length nor the pattern of BTV-8 viraemia and confirmed that real time RT-PCR remains positive although no circulating virus is detectable in the peripheral circulation.     

Antigen heterogeneity among Mycoplasma mycoides subsp. mycoides SC isolates: discrimination of major surface proteins

The protein and antigen profiles of 60 isolates, strains and the type strain PG1 of Mycoplasma mycoides subsp. mycoides SC were compared by sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblot analysis. Analysis using contagious bovine pleuropneumonia antisera and hyperimmune rabbit sera against several representative strains revealed some differences in protein profiles and variability in antigens among strains from different geographic regions. The most common antigenic bands had the molecular masses of 110, 95, 80, 69, 62, 60, 48, 44, 39 and 38 kDa. There were differences among European strains, where a larger group coming from Italy lacked the p98 antigen, thus, with one exception, distinguishing the Italian strains from Portuguese, French and Spanish strains. African, Australian and PG1 strains showed heterogenic profiles, with quantitative differences and in a few strains some antigenic bands were absent. The group constituting African, Australian and PG1 strains was characterised by the presence of 71.5/70 kDa antigens, which were not detected in European strains. Mycoplasma mycoides subsp. mycoides SC membrane proteins were characterised by Triton X-114 partitioning and p110, p98, p95, p62/60 and p48 were identified as immunogenic antigens. The simultaneous presence of these five antigens was common to all the sera examined and, therefore, indicates the diagnostic potential of immunoblotting. Most immunodominant antigens are surface-exposed proteins as determined by the trypsin treatment.     

Production of High Potency Anti-Teschen Disease Serum From Rabbits and Guinea Pigs

An antiserum of high antibody content against Teschen disease Konratice virus was obtained by inoculating rabbits and guinea pigs with an antigen composed of aluminum gel and virus propagated in swine kidney cell cultures. The rabbit and guinea pig serums neutralized 1,500 TCID₅₀ of virus at dilutions of 1:5,120 and 1:2,048, respectively. The antibody level in the rabbit serum was tenfold greater than that in convalescent swine serum. Rabbit serum neutralized 2.8 x 10⁶ plaque-forming units of the Konratice virus. At a dilution of 1:5,120, this serum neutralized 1,500 TCID₅₀ of the Reporyje virus. The methods used to prepare and assay the serum are described.     

Establishment of inflammatory model induced by Pseudorabies virus infection in mice

BackgroundPseudorabies virus (PRV) infection leads to high mortality in swine. Despite extensive efforts, effective treatments against PRV infection are limited. Furthermore, the inflammatory response induced by PRV strain GXLB-2013 is unclear.ObjectivesOur study aimed to investigate the inflammatory response induced by PRV strain GXLB-2013, establish an inflammation model to elucidate the pathogenesis of PRV infection further, and develop effective drugs against PRV infection.MethodsKunming mice were infected intramuscularly with medium, LPS, and different doses of PRV-GXLB-2013. Viral spread and histopathological damage to brain, spleen, and lung were determined at 7 days post-infection (dpi). Immune organ indices, levels of reactive oxygen species (ROS), nitric oxide (NO), and inflammatory cytokines, as well as levels of activity of COX-2 and iNOS were determined at 4, 7, and 14 dpi.ResultsAt 10⁵–10⁶ TCID₅₀ PRV produced obviously neurological symptoms and 100% mortality in mice. Viral antigens were detectable in kidney, heart, lung, liver, spleen, and brain. In addition, inflammatory injuries were apparent in brain, spleen, and lung of PRV-infected mice. Moreover, PRV induced increases in immune organ indices, ROS and NO levels, activity of COX-2 and iNOS, and the content of key pro-inflammatory cytokines, including interleukin (IL)-1β, IL-6, tumor necrosis factor-α, interferon-γ and MCP-1. Among the tested doses, 10² TCID₅₀ of PRV produced a significant inflammatory mediator increase.ConclusionsAn inflammatory model induced by PRV infection was established in mice, and 10² TCID₅₀ PRV was considered as the best concentration for the establishment of the model.     

Immunological characterization of breakdown peptides of the 104 kilodalton hemolysin of Actinobacillus pleuropneumoniae serotype 1

The 104 kilodalton (kDa) hemolysin of Actinobacillus pleuropneumoniae serotype 1, strain CM-5 was precipitated from RPMI-1640 culture supernatant using ammonium sulfate to 80% saturation. In immunoblots, a rabbit polyclonal antiserum against the 104 kDa hemolysin protein, recognized not only the original 104 kDa monomeric form of the hemolysin but other proteins in the crude antigen mixture ranging in molecular mass from 43 to greater than 125 kDa. The antiserum was able to crosslink these proteins to active hemolysin in RPMI-1640 culture supernatant resulting in bands of hemolysis in blood agar used in a contact assay. Corresponding to these bands of hemolysis, denatured peptides with molecular masses of 51, 85, 104 and greater than 125 kDa were excised and injected into rabbits. In immunoblots, the resultant antibodies recognized the injected peptide and the monomeric 104 kDa protein. However, only the rabbit antisera produced against the 104 and 125 kDa proteins contained antibodies which neutralized the active 104 kDa hemolysin in culture supernatant. These results indicate that (i) the 104 kDa protein hemolysin can exist in a higher molecular weight aggregate (greater than 125 kDa) but can also break down to peptides which have molecular masses smaller than the 104 kDa parent molecule and (ii) while several epitopes are present in the hemolysin molecule, there seems to be a restricted number of antigenic determinants responsible for inducing neutralizing antibodies and these seem to reside only in the 104 kDa parent molecule. This may have consequences, in terms of vaccine development, for the control of pleuropneumonia in swine herds.     

猪乙型脑炎病毒LS株的理化特性及其在BHK-21细胞上增殖特性的研究

对猪乙型脑炎病毒(Japanese encephalitis virus,JEV)LS株的理化特性及其在BHK-21细胞上的增殖特性进行研究,结果表明,该病毒对温度(56 ℃)、酸(pH 5.0以下)、乙醚、胰蛋白酶敏感,反复冻融(-65～20 ℃)3次几乎不影响病毒效价;该毒株在BHK-21细胞上连续传20代,仍能维持较高的病毒滴度(TCID₅₀=10^7.75/mL)和血凝效价(2⁸),且根据其在BHK-21细胞上的增殖规律,得到最佳收毒时间为接毒后28～40 h。本试验为进一步研究JEV LS株的生物学特性奠定基础。