Outbreak of variant pseudorabies virus in Bartha-K61-vaccinated piglets in central Shandong Province, China

Analysis of the recombination and evolution of the new type mutant pseudorabies virus XJ5 in China

Pseudorabies have caused enormous economic losses in China's pig industry and have recurred on many large pig farms since late 2011. The disease is caused by highly pathogenic, antigenic variant pseudorabies virus (vPRV) strains. Our laboratory isolated a pseudorabies virus in 2015 and named it XJ5. The pathogenic ability of this mutant strain was much stronger than that of the original isolate. After we sequenced its whole genome (GenBank accession number: OP512542), we found that its overall structure was not greatly changed compared with that of the previous strain Ea (KX423960.1). The whole genome alignment showed that XJ5 had a strong genetic relationship with the strains isolated in China after 2012 reported in GenBank. Based on the isolation time of XJ5 and the mutation and recombination analysis of programs, we found that the whole genome homology of XJ5 and other strains with Chinese isolates was greater than 95%, while the homology with strains outside Asia was less than 94%, which indicated that there may be some recombination and mutation patterns. We found that virulent PRV isolates emerged successively in China in 2011 and formed two different evolutionary clades from foreign isolates. At the same time, this may be due to improper immunization and the presence of wild strains in the field, and recent reports have confirmed that Bartha vaccine strains recombine with wild strains to obtain new pathogenic strains. We performed genetic evolution analysis of XJ5 isolated and sequenced in our laboratory to trace its possible mutations and recombination. We found that XJ5 may be the result of natural mutation of a virus in a branch of mutant strains widely existing in China.

Intradermal vaccination with Porcilis® Begonia can clinically protect against fatal PRV challenge with the highly virulent ZJ01 field strain

Since pseudorabies (PR) re-emerged and rapidly spread in China at the end of 2011, researchers have focused on effective vaccine strategies to prevent and control pseudorabies virus (PRV) infection in pig herds. Due to the extensive application of an attenuated vaccine based on the Bartha-K61 strain isolated in Hungary in 1961 and the variation of the PRV strain, it has been suggested that traditional vaccines based on the Bartha-K61 strain offer only partial protection against variant strains. It was therefore evaluated whether the Porcilis® Begonia vaccine, which is based on the NIA-3 strain with deletions in the gE and TK genes, is efficacious against experimental infection with the virulent, contemporary Chinese PRV strain ZJ01. In this study, piglets were vaccinated with Porcilis® Begonia through either the intradermal (ID) route or the intramuscular (IM) route and subsequently challenged intranasally with strain ZJ01 at 4 weeks post-vaccination. An unvaccinated challenge group and an unvaccinated/nonchallenged group were also included in the study. All animals were monitored for 14 days after challenge. Vaccinated and negative control pigs stayed healthy during the study, while the unvaccinated control animals developed lesions associated with PRV ZJ01 challenge, and 44% of these pigs died before the end of the experiment. This study demonstrated that ID or IM vaccination of pigs with a vaccine based on the NIA-3 strain Porcilis® Begonia clinically protects against fatal PRV challenge with the ZJ01 strain.

Molecular epidemiological and genetic characterization of pseudorabies virus in Guangxi, China

Pseudorabies virus (PRV) is an important pathogen that can cause harm to the pig population. Since 2011, there have been a number of large-scale outbreaks of pseudorabies on Chinese farms where animals had been vaccinated with the Bartha-K61 vaccine. In order to understand the epidemiological trend and genetic variations of PRV in Guangxi province, China, 819 tissue samples were collected from swine farms where PRV infection was suspected from 2013 to 2019, and these were tested for infectious wild strains of PRV. The results showed a positive rate of PRV in Guangxi province of 28.21% (231/819). Thirty-six wild-type PRV strains were successfully isolated from PRV-positive tissue samples, and a genetic evolutionary analysis was performed based on the gB, gC, gD, gE, and TK genes. Thirty of the PRV strains were found to be closely related to the Chinese variant strains HeN1-China-2012 and HLJ8-China-2013. In addition, five PRV strains were genetically related to Chinese classical strains, and one isolate was a recombinant of the PRV variant and the vaccine strain Bartha-K61. Amino acid sequence analysis showed that all 36 PRV strains had characteristic variant sites in the amino acid sequences of the gB, gC, gD, and gE proteins. Pathogenicity analysis showed that, compared to classical PRV strains, the PRV variant strains were more pathogenic in mice and had a lower LD50. Taken together, our results show that wild-type PRV infections are common on pig farms in Guangxi province of China and that the dominant prevalent strains were those of the PRV variants. The PRV variant strains also had increased pathogenicity in mice. Our data will provide a useful reference for understanding the prevalence and genetic evolution of PRV in China.

Pseudorabies gD protein protects mice and piglets against lethal doses of pseudorabies virus

Introduction

Pseudorabies (PR) is a highly contagious viral disease caused by the pseudorabies virus (PRV), which can cause disease in a wide range of domestic and wild animals. Studies have shown that new mutant strains have emerged in pig farms in many regions and that commercial inactivated and live attenuated vaccines are becoming less effective at protecting pigs.

Methods

Porcine pseudorabies glycoprotein D (gD) gene (GenBank: QEY95774.1) with hexa-His tag to the C terminus for further purification processes was cloned into the lentiviral expression plasmid pLV-CMV-eGFP by restriction enzyme, the resulting plasmid was designated as pLV-CMV-gD. HEK-293T cells with robust and stable expression of recombinant gD protein was established by infection with recombinant lentivirus vector pLV-CMV-gD. We expressed porcine pseudorabies virus gD protein using HEK-293T cells.

Results

We describe in this study that individual gD proteins produced by a mammalian cell expression system are well immunogenic and stimulate high levels of PRV-specific and neutralizing antibodies in mice and piglets. All mice and piglets survived lethal doses of PRV, significantly reducing the amount of PRV virus in piglets' lymph nodes, lungs, spleen, and other tissues. It also significantly reduced the time cycle and amount of viral excretion from piglets to the environment through the nasal and anal cavities.

Discussion

The results suggest that PRV gD protein is expected to be a potential candidate for the preparation of genetically engineered PR vaccines for the prevention of PRV infection and the control of PR epidemics.

Secondary metabolites of Bacillus subtilis L2 show antiviral activity against pseudorabies virus

Bacillus subtilis (B. subtilis) is a commercially important probiotic known to produce secondary metabolites with antibacterial, antifungal and anti-inflammatory activities. However, the potential ability of B. subtilis to combat viruses, especially DNA viruses, has not been extensively investigated. In this study, we identified two distinct B. subtilis strains and examined the efficiency of their secondary metabolites against pseudorabies virus (PRV), a swine herpesvirus resulting in economic losses worldwide. We found that treatment with the secondary metabolites of B. subtilis L2, but not the metabolites of B. subtilis V11, significantly inhibited PRV replication in multiple cells. Notably, the antiviral activity of the metabolites of B. subtilis L2 was thermal stable, resistant to protease digestion. Moreover, these metabolites effectively impeded PRV binding, entry and replication. Importantly, oral administration of the metabolites of B. subtilis L2 protected mice from lethal PRV infection, rescuing weight loss and reducing the viral load in vivo. In summary, our results reveal that the metabolites of B. subtilis L2 exhibit anti-PRV activity both in vitro and in vivo, providing a potential candidate for novel antiviral drugs.

Antiviral Activity of Benzoheterocyclic Compounds from Soil-Derived Streptomyces jiujiangensis NBERC-24992

Pseudorabies virus (PRV) is a pathogen that causes Aujeszky's disease (AD) in animals, leading to huge economic losses to swine farms. In order to discover anti-PRV compounds, we studied the extracts of the strain Streptomyces jiujiangensis NBERC-24992, which showed significant anti-PRV activity. Eight benzoheterocyclic secondary metabolites, including three new compounds (1-3, virantmycins D-G) and five known compounds (4-8, virantmycin, A-503451 D, A-503451 D acetylate, A-503451 A, and A-503451 B), were isolated from the broth of NBERC-24992. The structures of the new compounds were identified by using extensive spectroscopic data, including mass spectrometry (MS), nuclear magnetic resonance (NMR), and electronic circular dichroism (ECD). Compound 1 was found to be a novel heterocyclic compound with a tricyclic skeleton from natural product. All compounds were tested for antiviral activity, and 4 (virantmycin) showed an excellent effect against PRV and was better than ribavirin and acyclovir. Our study revealed that chlorine atom and tetrahydroquinoline skeleton were important active moiety for antiviral activity. Virantmycin could be a suitable leading compound for an antiviral drug against PRV.

Antiviral activity of dandelion aqueous extract against pseudorabies virus both in vitro and in vivo

Pseudorabies virus (PRV) is one of the most significant pathogens of swine. In recent years, the continual emergence of novel PRV variants has caused substantial economic losses in the global pig industry. PRV can infect humans leading to symptoms of acute encephalitis with implications for public health. Thus, new measures are urgently needed to prevent PRV infection. This study evaluated the anti-PRV capability of dandelion aqueous extract (DAE) in vitro and in vivo. DAE was found to inhibit the multiplication of the PRV TJ strain in PK15 cells in a concentration-dependent manner, with a 50% inhibitory concentration (IC₅₀) of 0.2559 mg/mL and a selectivity index (SI) of 14.4. DAE inhibited the adsorption and replication stages of the PRV life cycle in vitro, and the expression of IE180, EP0, UL29, UL44, and UL52 was inhibited in the presence of DAE. In vivo experiment results of mice show that a 0.5 g/kg dose of DAE injected intraperitoneally protected 28.6% of the mice from the lethal challenge; decreased the viral load in the liver, lung, brain, heart, and kidney of PRV-infected mice; and attenuated brain damage caused by PRV infection. Furthermore, DAE could also ameliorate viral infection through regulation of the levels of cytokines (IFN-γ, TNF-α, and IL-4) in PRV-infected mouse serum. These results demonstrated that DAE exhibited potent inhibitory capability against PRV infection in vitro and in vivo; DAE is therefore expected to be a candidate TCM herb for use against PRV infection.

Napyradiomycin A4 and Its Relate Compounds, a New Anti-PRV Agent and Their Antibacterial Activities, from Streptomyces kebangsaanensis WS-68302

Two new napyradiomycins derivatives, napyradiomycin A4 (1) and A80915 H (2), along with five known ones, were isolated from the ethyl acetate extract of fermentation culture of Streptomyces kebangsaanensis WS-68302. Their structures were elucidated by extensive spectroscopic analysis, including HR-MS, 1D and 2D NMR, CD spectrum, as well as comparison with literature data. Compound 1 exhibited significant antiviral activity against PRV (Pseudorabies virus) with an IC₅₀ value of 2.056 μM and therapeutic ratio at 14.98, suggesting that it might have potential for development of an antiviral agent. Moreover, compound 1 displayed the strongest inhibition against PRV protein among the tested napyradiomycins in the indirect immunofuorescence assay. Compounds 3 and 4 showed higher activities against swine pathogenic Streptococcus suis than the positive control penicillin G sodium salt, with MIC values of 3.125 and 6.25 μg/mL, respectively. Compounds 1 and 3-6 exhibited moderate antibacterial activity against the swine pathogenic Erysipelothrix rhusiopathiae, with MIC values ranging from 25 to 50 μg/mL.

Progress on innate immune evasion and live attenuated vaccine of pseudorabies virus

Pseudorabies virus (PRV) is a highly infectious disease that can infect most mammals, with pigs as the only natural host, has caused considerable economic losses to the pig husbandry of the world. Innate immunity is the first defense line of the host against the attack of pathogens and is essential for the proper establishment of adaptive immunity. The host uses the innate immune response to against the invasion of PRV; however PRV makes use of various strategies to inhibit the innate immunity to promote the virus replication. Currently, live attenuated vaccine is used to prevent pig from infection with the PRV worldwide, such as Bartha K61. However, a growing number of data indicates that these vaccines do not provide complete protection against new PRV variants that have emerged since late 2011. Here we summarized the interactions between PRV and host innate immunity and the current status of live attenuated PRV vaccines to promote the development of novel and more effective PRV vaccines.

Comparison of the protective efficacy between the candidate vaccine ZJ01R carrying gE/gI/TK deletion and three commercial vaccines against an emerging pseudorabies virus variant

Pseudorabies virus (PRV) is a swine alpha-herpesvirus that mainly causes reproductive disorders in sows and neurological diseases in piglets. Vaccination is the most efficient method to prevent the disease. In China, since the emergence of PRV mutant strains in late 2011, the traditional commercial vaccines have not been providing complete protection. Our previous studies have demonstrated that PRV ZJ01 is a highly virulent strain, and its derivative, ZJ01R, which carries the gE/gI/TK gene deletion, could provide protection against the variant PRV challenge. However, the difference in immune efficacy between ZJ01R and other commercial vaccines remains unclear. In this study, the immune protection efficacy between ZJ01R and three commercial PRV vaccines (Bartha-K61, HB2000, and SA215) was evaluated in piglets. The safety of ZJ01R was shown to be equivalent to that of the three commercial vaccines. The titers of the neutralizing antibodies against the PRV classical strain LA in the four vaccine groups were similar, while the anti-PRV variant neutralizing antibody titers in the ZJ01R group were significantly higher than those in the Bartha-K61, HB2000, and SA215 strain groups. After the PRV challenge, ZJ01R, HB2000, and SA215 vaccinations could provide complete protection, whereas the Bartha-K61 vaccination could only provide 60 % protection. Importantly, the rectal viral excretion and PRV DNA loads in the lung tissues in the ZJ01R group were significantly lower than those in the Bartha-K61, HB2000, and SA215 groups. Altogether, these results indicated that ZJ01R could provide higher protection efficacy against the PRV virulent ZJ01 challenge than the three commercial PRV gene-deleted live vaccines derived from the classical vaccine strains, providing the potential to develop a new PRV vaccine to control the epidemic PRV variant strains in the future.

Glycerol Monolaurate to Ameliorate Efficacy of Inactivated Pseudorabies Vaccine

The present study is aimed to evaluate the effect of glycerol monolaurate (GML) on the growth performance and immune enhancement of pseudorabies virus (PRV)-inactivated vaccine in the early-weaned piglets. One hundred and twenty-five 28-day-old weaned piglets were randomly assigned to a control group (CON, no vaccine and no challenge), challenge control group (C-CON), inactivated PRV vaccine group (IPV), IPV + 500 mg/kg GML group (L-GML), and IPV + 1,000 mg/kg GML group (H-GML) during the entire 28-day experimental period. All the data analyses were performed by one-way analysis of variance (ANOVA) and multiple comparisons. Our results showed that the final weight, average daily gain (ADG), and average daily feed intake (ADFI) of H-GML were the highest in each group, and F/G of H-GML was increased but there was no significant difference with CON (p > 0.05). Levels of PRV glycoprotein B (gB) antibody and immunoglobulin in serum of L-GML and H-GML were higher than those of IPV, but only gB antibody levels and immunoglobulin G (IgG) in H-GML were significantly increased (p < 0.05). Compared with IPV, the contents of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) in serum of L-GML (TNF-α and IL-1β: p > 0.05, IL-6: p < 0.05, respectively) and H-GML (p < 0.01, both) were all decreased, and the content of interleukin-10 (IL-10) in H-GML was increased (p > 0.05). Furthermore, reverse transcription-polymerase chain reaction (RT-PCR) experiments proved that L-GML and H-GML were both superior to IPV in inhibiting the expression of TNF-α (p < 0.01), IL-6 (p > 0.05), and IL-1β (p < 0.01) mRNAs and promoting the expression of IL-10 mRNA (L-GML: p > 0.05, H-GML: p < 0.05, respectively) in the superficial inguinal lymph nodes. Histopathological examination found mild congestion in the lung and inguinal lymph nodes of IPV, while the tissues (brain, lung, and inguinal lymph nodes) of L-GML and H-GML were the same as CON with no obvious lesions. The above results indicate that GML may improve the growth performance of weaned piglets and enhance the immunity of PRV-inactivated vaccine by increasing the levels of PRV gB antibody and immunoglobulin and regulating cytokine levels.

Pseudorabies Virus: From Pathogenesis to Prevention Strategies

Pseudorabies (PR), also called Aujeszky’s disease (AD), is a highly infectious viral disease which is caused by pseudorabies virus (PRV). It has been nearly 200 years since the first PR case occurred. Currently, the virus can infect human beings and various mammals, including pigs, sheep, dogs, rabbits, rodents, cattle and cats, and among them, pigs are the only natural host of PRV infection. PRV is characterized by reproductive failure in pregnant sows, nervous disorders in newborn piglets, and respiratory distress in growing pigs, resulting in serious economic losses to the pig industry worldwide. Due to the extensive application of the attenuated vaccine containing the Bartha-K61 strain, PR was well controlled. With the variation of PRV strain, PR re-emerged and rapidly spread in some countries, especially China. Although researchers have been committed to the design of diagnostic methods and the development of vaccines in recent years, PR is still an important infectious disease and is widely prevalent in the global pig industry. In this review, we introduce the structural composition and life cycle of PRV virions and then discuss the latest findings on PRV pathogenesis, following the molecular characteristic of PRV and the summary of existing diagnosis methods. Subsequently, we also focus on the latest clinical progress in the prevention and control of PRV infection via the development of vaccines, traditional herbal medicines and novel small RNAs. Lastly, we provide an outlook on PRV eradication.

Epidemiological Investigation of Porcine Pseudorabies Virus in Hebei Province, China, 2017–2018

Pseudorabies (PR) is a serious disease affecting the pig industry in China, and it is very important to understand the epidemiology of pseudorabies virus (PRV). In the present study, 693 clinical samples were collected from Bartha-K61 vaccinated pigs with symptoms of suspected PRV infection between January 2017 and December 2018. All cases were referred for full clinical autopsy with detailed examination of histopathological examination, virus isolation and genetic evolution analysis of the PRV glycoprotein E (gE) gene. In addition, PRV gE antibodies in 3,449 serum samples were detected by the enzyme-linked immunosorbent assay (ELISA). The clinical data revealed that abortion and stillbirth are the most frequent appearances in pregnant sows of those cases. Histopathological examination exhibited a variety of pathological lesions, such as lobar pneumonia, hepatitis, lymphadenitis, nephritis, and typical nonsuppurative encephalitis. A total of 248 cases tested positive for the PRV gE gene. 11 PRV variants were isolated and confirmed by gE gene sequencing and phylogenetic analysis. These strains had 97.1%-100.0% nucleotide homology with the PRV reference strains. Notably, the isolated strains were highly homologous and clustered in the same branch as HSD-1/2019, which caused human acute encephalitis. Serological tests showed that the positive rate of PRV gE antibody in the 3449 serum samples collected from the Hebei Province was 46.27%. In conclusion, PRV variant strains Are high prevalence in the Hebei Province, which not only causes huge economic losses to the breeding industry but also potentially poses a threat to public health.

The Epidemiological Analysis of Pseudorabies Virus and Pathogenicity of the Variant Strain in Shandong Province

Pseudorabies (PR) is a disease that is seriously endangering the pig industry in China. To understand the current prevalence of pseudorabies virus (PRV) in Shandong Province, China, 19,292 serum samples were collected from 16 locations in Shandong from 2018 to 2020. The gE antibody was detected by enzyme-linked immunosorbent assay. Ninety-seven suspected cases of PRV infection were collected from sick pigs vaccinated with Bartha-K61 to isolate PRV. The results showed that the average positive rate of the PRV gE antibody decreased from 38.20% in 2018 to 18.12% in 2020, but there was a high positive rate in sows. The isolation rate of PRV was 13.40% (13/97), and four strains were purified through plaque assay (named PRV-SD1, PRV-SD2, PRV-SD3, and PRV-SD4). The homology and genetic evolution of four PRV strains based on gE, gC, gI, and TK genes were analyzed and showed that these four strains shared more than 99.0% nucleotide homology with the variant PRV XJ5 strain, and they clustered in the same sub-branch with the domestic variant PRV strains, including JS-2012 and XJ5. Furthermore, the pathogenicity of the isolated variant strain was assessed by intranasal infection of 16-week-old pigs with 1 mL PRV-SD1 strain. The results of the animal experiment demonstrated that the PRV-SD1–infected pigs exhibited obvious clinical symptoms as early as 2 days post inoculation (dpi), and all infected pigs died within 1 week. The severe hyperemia of meninges and swelling of lungs and tonsils were observed. Histopathology analysis showed the obvious lymphocytes necrosis of tonsils, interstitial pneumonia, and viral encephalitis. Many positive staining cells were observed in tonsils and brains through immunohistochemistry staining assay. Viral shedding in oropharyngeal and rectal swabs were detected at 2 dpi, reached a peak at 3 dpi, and then gradually decreased. The detection of viral loads in the tissues showed that tonsils had the highest virus titer, further proving it may be the target organ of variant PRV infection. In conclusion, variant PRV strains were still highly prevalent in Shandong Province, and they had a strong pathogenicity in pigs.

A natural product, (S)-10-Hydroxycamptothecin inhibits pseudorabies virus proliferation through DNA damage dependent antiviral innate immunity

Pseudorabies virus (PRV), a member of the subfamily alphaherpesvirinae, is one of the most important pathogenes that cause acute death in infected pigs and leads to substantial economic losses in the global swine industry. Recently, China's emerging PRV mutant strains resulted in the traditionally commercial vaccines not providing complete protection. Some studies reported that PRV could infect humans and cause endophthalmitis and encephalitis under certain circumstances. It is necessary to develop alternative manners to control the virus infection. Here, by screening a library of natural products, (S)-10-Hydroxycamptothecin (10-HCPT) was revealed to inhibit PRV replication with a selective index of 270.04. And 10-HCPT inhibited PRV replication by blocking the viral genome replication but not inhibiting the viral attachment, internalization, and release. RNA interference assay showed that 10-HCPT inhibited PRV replication by targeting DNA topoisomerase 1 (TOP1). Meanwhile, 10-HCPT treatment induced DNA damage response and stimulated antiviral innate immunity. Animal challenge experiments showed that 10-HCPT effectively alleviated clinical signs and hispathology, and increased INF-β responses in lung and brain tissues of mice induced by PRV infection. The results demonstrate that 10-HCPT is a promising therapeutic agent to control PRV infection.

Construction of a quadruple gene-deleted vaccine confers complete protective immunity against emerging PRV variant challenge in piglets

Background

Pseudorabies virus (PRV) causes Aujeszky’s disease or pseudorabies (PR) in pigs worldwide, which leads to heavy economic losses to the swine industry. Pigs are the natural host, meanwhile, animals such as dogs, cats, foxes, rabbits, cattle and sheep are susceptible to infection. In 2011, the emerging PRV variant led to the outbreak of PR in Bartha-K61 vaccinated pigs. The PR outbreaks demonstrated that the Bartha-K61 vaccine did not provide full protection against the emerging PRV variant. It is widely believed that PRV live attenuated vaccine could control PRV infection.

Methods

In this study, we developed a novel PRV live attenuated vaccine by deleting its gI, gE, US9, and US2 genes through CRISPR/Cas9, which was named PRV GDFS-delgI/gE/US9/US2.

Results

Safety experiments confirmed that PRV GDFS-delgI/gE/US9/US2 was safe for 5- to 7-day-old suckling piglets. Piglets immunized with the PRV GDFS-delgI/gE/US9/US2 vaccine did not produce PRV gE-specific antibodies but could generate PRV gB-specific antibodies and high neutralizing titers against the PRV GDFS strain (variant PRV strain) or PRV Ea strain (older PRV strain). After challenge with the emerging PRV GDFS variant, none of the piglets immunized with the PRV GDFS-delgI/gE/US9/US2 vaccine showed any clinical signs, and their rectal temperatures were normal. Moreover, the autopsy and histopathological analyses revealed that the piglets in the PRV GDFS-delgI/gE/US9/US2 vaccine group did not show apparent gross or pathological lesions. Furthermore, the piglets in the PRV GDFS-delgI/gE/US9/US2 vaccine groups did not present weight loss. According to the criteria of the OIE terrestrial manual, the results of the experiment confirmed that the PRV GDFS-delgI/gE/US9/US2 vaccine could provide full protection against the emerging PRV variant strain in piglets.

Conclusions

The PRV GDFS-delgI/gE/US9/US2 strain is a potential new live attenuated vaccine against emerging PRV variant strain infections in China.

Pathogenicity and immunogenicity of a gI/gE/TK/UL13-gene-deleted variant pseudorabies virus strain in swine

Pseudorabies is a highly infectious disease with severe clinical symptoms, causing acute death in infected pigs and leading to substantial economic losses among swine producers. In this study, a vaccine candidate strain in which the protein kinase UL13 gene was deleted was constructed with the CRISPR/Cas9 system based on the recombinant pseudorabies virus (PRV) ZJ01-ΔgI/gE/TK. Pigs immunized with ZJ01-ΔgI/gE/TK or ZJ01-ΔgI/gE/TK/UL13 produced high levels of anti-gB antibodies and virus-neutralizing antibodies. ZJ01-ΔgI/gE/TK/UL13 provided greater protective efficacy against challenge with PRV variant strain ZJ01 than did Bartha-K61 or ZJ01-ΔgI/gE/TK. The pigs vaccinated with ZJ01-ΔgI/gE/TK/UL13 excreted significantly less virus than those vaccinated with Bartha-K61 or ZJ01-ΔgI/gE/TK. The viral loads in the lungs of pigs treated with ZJ01-ΔgI/gE/TK/UL13 were lower than those in pigs treated with ZJ01-ΔgI/gE/TK after challenge with PRV variant strain ZJ01. These data indicated that ZJ01-ΔgI/gE/TK/UL13 had greater protective efficacy and safety than the commercial ZJ01-ΔgI/gE/TK and Bartha-K61 vaccines, and could be developed as a promising vaccine candidate for the prevention and control of this disease.

Current Status and Challenge of Pseudorabies Virus Infection in China

Pseudorabies (PR), also called Aujeszky’s disease, is a highly infectious disease caused by pseudorabies virus (PRV). Without specific host tropism, PRV can infect a wide variety of mammals, including pig, sheep, cattle, etc., thereby causing severe clinical symptoms and acute death. PRV was firstly reported in China in 1950s, while outbreaks of emerging PRV variants have been documented in partial regions since 2011, leading to significant economic losses in swine industry. Although scientists have been devoting to the design of diagnostic approaches and the development of vaccines during the past years, PR remains a vital infectious disease widely prevalent in Chinese pig industry. Especially, its potential threat to human health has also attracted the worldwide attention. In this review, we will provide a summary of current understanding of PRV in China, mainly focusing on PRV history, the existing diagnosis methods, PRV prevalence in pig population and other susceptible mammals, molecular characteristics, and the available vaccines against its infection. Additionally, promising agents including traditional Chinese herbal medicines and novel inhibitors that may be employed to treat this viral infection, are also discussed.

Emergence of a novel pathogenic recombinant virus from Bartha vaccine and variant pseudorabies virus in China

Pseudorabies virus (PRV), the causative agent of Aujeszky's disease, has resulted in substantial economic losses in the swine industry worldwide. Previous reports have shown that the PRV variant is responsible for the Pseudorabies outbreaks in Bartha-K61-vaccinated farms in China. However, there is limited information about the evolution of recombination of the PRV variant. Here, we isolated two PRV variants from a Bartha-K61-vaccinated swine farm, named them the JSY7 and JYS13 strains, analysed their complete genomic sequences and evaluated pathogenicity. As results, the JSY7 and JSY13 strains showed different cytopathic effects and plaque sizes. The JSY7 and JSY13 strains had the same Aspartate insertions in the gE protein as other PRV variants. The JSY7 and JSY13 strains were clustered into the same clade based on a genomic phylogenetic analysis. However, the JSY7 strain was relatively close to recent PRV isolates in China, while the JSY13 strain was more closely related to earlier PRV isolates. Interestingly, the gC gene phylogenetic tree showed that the JSY7 strain belonged to genotype II lineage 3, while the JSY13 strain belonged to genotype I and is the same branch with the Bartha strain. Furthermore, the PRV variants were relatively distant from the Bartha strain in the phylogenetic analysis of the gB, gC and gD genes. Importantly, a recombination analysis showed that the JSY13 strain might be a natural recombinant between the minor parental genotype I Bartha strain and the major parental genotype II JSY7 strain. Finally, we also found that the JSY13 strain showed a moderate virulence compared to the JSY7 strain in mice. Taken together, our data provide direct evidence for genomic recombination of PRV in nature, which may play an important role in the evolution and virulence of PRV. This discovery suggests that live PRV vaccine can act as genetic donors for genomic recombination.

Characterization of Nucleocytoplasmic Shuttling of Pseudorabies Virus Protein UL46

Pseudorabies virus (PRV) is the etiological agent of Aujeszky's disease, which has caused severe economic loss in China since its re-emergence in 2011. UL46, a late gene of herpesvirus, codes for the abundant but non-essential viral phosphoproteins 11 and 12 (VP11/12). In this study, VP11/12 was found to localize inside both the nucleus and cytoplasm. The nuclear localization signal (NLS) of VP11/12 was identified as ³RRARGTRRASWKDASR¹⁸. Further research identified α5 and α7 to be the receptors for NLS and the chromosome region maintenance 1 (CRM1) to be the receptor for the nuclear export signal. Moreover, we found that PRV VP11/12 interacts with EP0 and the stimulator of interferon genes protein (STING), whereas the NLS of VP11/12 is the important part for VP11/12 to interact with UL48. To our knowledge, this is the first study to provide reliable evidence verifying the nuclear localization of VP11/12 and its role as an additional shuttling tegument protein for PRV. In addition, this is also the first study to elucidate the interactions between PRV VP11/12 and EP0 as well as between PRV VP11/12 and STING, while identifying the precise interaction sites of PRV VP11/12 and VP16.

The pseudorabies virus R2 non-neuroinvasive vaccine: A proof-of-concept study in pigs

Neurotropic alpha-herpesviruses that infect mammals establish life-long latent infections in the peripheral nervous system after initial infection of exposed mucosal tissues. The neuroinvasive properties can lead to severe complications both with clinical and veterinary alpha-herpesviruses, and vaccines are often unavailable or provide limited protection. Here we assess the properties and efficacy of an R2 vaccine derived from the alpha-herpesvirus, pseudorabies virus (PRV), in pigs. We demonstrate that the PRV R2 vaccine does not invade the porcine peripheral nervous system within the limits of detection. Furthermore, after a single intranasal vaccination, R2 conferred protection to pigs subsequently challenged with a virulent PRV field strain (NIA-3). These findings support that the R2 vaccine design is non-neuroinvasive and is an effective vaccine in the context of a natural host.

Pseudorabies virus (PRV) strain with defects in gE, gC, and TK genes protects piglets against an emerging PRV variant

The prevalence of an emerging variant of the pseudorabies virus (PRV) has been causing serious losses to farmers in China. Moreover, the commercially available PRV vaccine often fails to provide thorough protection. Therefore, in this study, we generated a PRV-∆gC\gE∆TK strain with defects in gC, gE, and TK of PRV. Compared to the parental PRV strain and the single gene deletion strains (PRV-∆gC, PRV-∆gE, and PRV-∆TK), PRV-∆gC\gE∆TK grew slowly, and exhibited fewer and smaller plaques on swine testis (ST) cells. Furthermore, animal experiment results showed that mice that were immunized intramuscularly with PRV-∆gC\gE∆TK, survived throughout the experiment with no observed clinical symptoms, and were completely protected against PRV challenge. Additionally, deletion of the gC, gE, and TK genes significantly alleviated viral damage in the brain. Furthermore, one-day-old weaned piglets immunized intramuscularly with PRV-∆gC\gE∆TK elicited higher levels of gB antibodies against both the emerging PRV variant and the parental PRV, exhibited full protection against challenge with both variants, and showed neutralization capacity against PRV. These data suggest that PRV-∆gC\gE∆TK is a promising vaccine candidate for the control of pseudorabies.

Safety and immunogenicity of an attenuated Chinese pseudorabies variant by dual deletion of TK&gE genes

Background

Since the outbreak of a new emerging virulent pseudorabies virus mutant in Chinese pig herds, intensive research has been focused on the construction of novel gene deletion vaccine based on the variant virulent viruses. An ideal vaccine candidate is expected to have a balanced safety and immunogenicity.

Results

From the infectious clone of PRV AH02LA strain, a TK deletion mutant was generated through two-step Red mutagenesis. After homologous recombination with a transfer vector, a TK&gE dual deficient mutant PRV (PRV^ΔTK&gE-AH02) was generated, and its structure verified by PCR, RFLP and sequencing. Growth kinetics test showed that PRV^ΔTK&gE-AH02 reached a titer of 10^7.5 TCID₅₀ /mL on ST cells.

The PRV^ΔTK&gE-AH02 at a dose of 10^6.0 TCID₅₀ /animal was not virulent in mice or 1-day-old piglets with maternal PRV antibodies. No clinical signs or virus shedding were detected in 28~ 35-day-old piglets without maternal PRV antibodies after nasal or intramuscular administration with a dose of 10^6.0 TCID₅₀, although it caused one death of four 1-day-old piglets without maternal PRV antibodies. In the efficiency test of PRV^ΔTK&gE-AH02, all four 28~ 35-day-old piglets without PRV antibody in the challenge control showed typical clinical symptoms and virus shedding, and two died at 4~ 5 days post challenge. All piglets in 10^5.0, 10^4.0 and 10^3.0 TCID₅₀/dose PRV^ΔTK&gE-AH02 groups provided complete protection against challenge at only 7 days post intramuscular vaccination. More importantly, PRV^ΔTK&gE-AH02 stopped virus shedding in these piglets. In contrast, all four piglets in PRV Bartha K61 vaccine group developed high body temperature (≥40.5 °C) and viral shedding, despite they had mild or even no clinical symptoms.

Conclusions

The constructed TK&gE dual deletion mutant PRV^ΔTK&gE-AH02 can reach high titers on ST cells. The live vaccine of PRV^ΔTK&gE-AH02 is highly safe, and can not only provide clinical protection but also stops virus shedding. This study suggests that PRV^ΔTK&gE-AH02 might work as a promising vaccine candidate to combat the PRV variant emerging in Chinese herds since 2011.

Identification and characterization of G-quadruplex formation within the EP0 promoter of pseudorabies virus

EP0 is an important early gene that modulates the life cycle of pseudorabies virus (PRV). A guanine-rich sequence overlapping with three Sp1 binding sites is located upstream of the transcription start site (TSS) in the EP0 promoter. Using native polyacrylamide gel electrophoresis (PAGE) and circular dichroism (CD), we verified that the G-rich region in the EP0 promoter forms an intramolecular parallel G-quadruplex (G4) in the presence of K⁺ ions. Further dimethyl sulphate (DMS) footprinting and Taq polymerase stop assays indicates the potential polymorphic folding of G4. In addition, a small chemical ligand, pyridostatin (PDS), promotes and stabilizes the formation of G4. Interestingly, based on the results of electrophoretic mobility shift assays (EMSA), the Sp1 protein bound to G4-bearing DNA with more affinity than DNA lacking the G4 structure. According to the luciferase reporter assay, G4 negatively regulates the EP0 promoter activity. These results demonstrate that Sp1 and G4 cooperate to regulate EP0 promoter activity.

Antiviral Effect of Resveratrol in Piglets Infected with Virulent Pseudorabies Virus

Pseudorabies virus (PRV) is one of the most important pathogens of swine, resulting in devastating disease and economic losses worldwide. Nevertheless, there are currently no antiviral drugs available for PRV infection. Resveratrol (Res) was identified to exert its antiviral activity by inhibiting the PRV replication in preliminary investigations. In our previous study, we found that Res has anti-PRV activity in vitro. Here, we show that Res can effectively reduce the mortality and increase the growth performance of PRV-infected piglets. After Res treatment, the viral loads significantly (p < 0.001) decreased. Pathological symptoms, particularly inflammation in the brain caused by PRV infection, were significantly (p < 0.001) relieved by the effects of Res. In Res-treated groups, higher levels of cytokines in serum, including interferon gama, interleukin 12, tumor necrosis factor-alpha and interferon alpha were observed at 7 days post infection. These results indicated that Res possesses potent inhibitory activity against PRV-infection through inhibiting viral reproduction, alleviating PRV-induced inflammation and enhancing animal immunity, suggesting that Res is expected to be a new alternative control measure for PRV infection.

Seroprevalence and associated risk factors of pseudorabies in Shandong province of China

A cross-sectional serological study was conducted in Shandong province of China to determine the seroprevalence and risk factors associated with seropositivity due to pseudorabies virus (PRV) infection in small- and medium-sized farrow-to-finish herds following outbreaks of variant PRV strains. A total of 6,035 blood samples from 224 randomly selected herds were screened. The results showed that 25.0% of the herds and 56.7% of the serum samples were seropositive for field strains of PRV. Herds consisting of 50–100 breeding sows had higher herd seroprevalence and serum sample seroprevalence than larger herds. Both the highest herd seroprevalence and highest serum sample seroprevalence were observed in western Shandong, followed northern Shandong. Based on univariate analysis, the following risk factors were utilized in subsequent multivariable logistic regression analysis: region, herd size, weight of purchased gilts, and all-in/all-out practice. Upon multivariate analysis, region, herd size, weight of purchased gilts and all-in/all-out practice were significantly associated with PRV herd seropositivity. These findings indicate that we are facing a serious situation in the prevention and control of pseudorabies. The results could help predict the next outbreak and set out control measures.

Bartha-k61 vaccine protects growing pigs against challenge with an emerging variant pseudorabies virus

Since late 2011, pseudorabies (PR) has resurfaced in many large pig farms, causing great economic loss for the swine industry in China. The PRV variant strain with high virulence and antigenic variation has been considered to be the main cause, and much attention has been focused on how to prevent and control the reoccurrence of this disease in China. In this study, two kinds of vaccination strategy were employed to evaluate the protective effects of Bartha-k61vaccine against both variant PRV (XJ5) and classical PRV (Ra) strain challenge. Humoral immunity response, clinical signs, survival rate, body weight, virus shedding and pathology were assessed in commercial pigs. The results showed that Bartha-k61vaccine, administered either once or twice, was effective against the PRV variant (XJ5) challenge, while no significant differences were observed between single and prime-boost vaccinated pigs. However, pigs vaccinated twice had better body weight gains than those vaccinated once, following challenge with the classical PRV strain (Ra) (p<0.01). Therefore, the Bartha-k61 vaccine appears to be an effective vaccine to control the spread of PRV variants in China in the absence of new powerful candidate vaccines specific to these PRV strains.

Outbreak of severe pseudorabies virus infection in pig-offal-fed farmed mink in Liaoning Province, China

An outbreak of severe pseudorabies virus (PRV) infection in farmed mink occurred in northern China in late 2014, causing significant economic losses in the local fur industry. Here, we report the first case of a PRV outbreak in mink in northeastern China, caused by feeding farmed mink with raw pork or organs contaminated by PRV. Mink infected with virulent PRV exhibited diarrhea, neurologic signs, and higher mortality, which can be misdiagnosed as highly pathogenic mink enteritis virus (MEV), canine distemper virus (CDV), and food poisoning. However, these were excluded as causative agents by PCR or bacteria isolation. The duration of disease was 3-7 days, and the mortality rate was 80-90%. PRV was characterized using indirect immunofluorescence assays (IFA) and electron microscopy (EM). Phylogenetic analysis based on full-length genome sequences and those of individual genes of this novel virus strain showed that it clustered in an independent branch with several other PRV isolates from China.

Recombinant Pseudorabies Virus (PRV) Expressing Firefly Luciferase Effectively Screened for CRISPR/Cas9 Single Guide RNAs and Antiviral Compounds

A Pseudorabies virus (PRV) variant has emerged in China since 2011 that is not protected by commercial vaccines, and has not been well studied. The PRV genome is large and difficult to manipulate, but it is feasible to use clustered, regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology. However, identification of single guide RNA (sgRNA) through screening is critical to the CRISPR/Cas9 system, and is traditionally time and labor intensive, and not suitable for rapid and high throughput screening of effective PRV sgRNAs. In this study, we developed a recombinant PRV strain expressing firefly luciferase and enhanced green fluorescent protein (EGFP) as a reporter virus for PRV-specific sgRNA screens and rapid evaluation of antiviral compounds. Luciferase activity was apparent as soon as 4 h after infection and was stably expressed through 10 passages. In a proof of the principle screen, we were able to identify several PRV specific sgRNAs and confirmed that they inhibited PRV replication using traditional methods. Using the reporter virus, we also identified PRV variants lacking US3, US2, and US9 gene function, and showed anti-PRV activity for chloroquine. Our results suggest that the reporter PRV strain will be a useful tool for basic virology studies, and for developing PRV control and prevention measures.

Genetic Diversity and Positive Selection Analysis of Classical Swine Fever Virus Envelope Protein Gene E2 in East China under C-Strain Vaccination

Classical swine fever virus (CSFV) causes an economically important and highly contagious disease of pigs worldwide. C-strain vaccination is one of the most effective ways to contain this disease. Since 2014, sporadic CSF outbreaks have been occurring in some C-strain vaccinated provinces of China. To decipher the disease etiology, 25 CSFV E2 genes from 169 clinical samples were cloned and sequenced. Phylogenetic analyses revealed that all 25 isolates belonged to subgenotype 2.1. Twenty-three of the 25 isolates were clustered in a newly defined subgenotype, 2.1d, and shared some consistent molecular characteristics. To determine whether the complete E2 gene was under positive selection pressure, we used a site-by-site analysis to identify specific codons that underwent evolutionary selection, and seven positively selected codons were found. Three positively selected sites (amino acids 17, 34, and 72) were identified in antigenicity-relevant domains B/C of the amino-terminal half of the E2 protein. In addition, another positively selected site (amino acid 200) exhibited a polarity change from hydrophilic to hydrophobic, which may change the antigenicity and virulence of CSFV. The results indicate that the circulating CSFV strains in Shandong province were mostly clustered in subgenotype 2.1d. Moreover, the identification of these positively selected sites could help to reveal molecular determinants of virulence or pathogenesis, and to clarify the driving force of CSFV evolution in East China.