Genome Characteristics and Evolution of Pseudorabies Virus Strains in Eastern China from 2017 to 2019

Simultaneous Detection of Porcine Respiratory Coronavirus, Porcine Reproductive and Respiratory Syndrome Virus, Swine Influenza Virus, and Pseudorabies Virus via Quadruplex One-Step RT-qPCR

Porcine respiratory coronavirus (PRCoV), porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), and pseudorabies virus (PRV) are significant viruses causing respiratory diseases in pigs. Sick pigs exhibit similar clinical symptoms such as fever, cough, runny nose, and dyspnea, making it very difficult to accurately differentially diagnose these diseases on site. In this study, a quadruplex one-step reverse-transcription real-time quantitative PCR (RT-qPCR) for the detection of PRCoV, PRRSV, SIV, and PRV was established. The assay showed strong specificity, high sensitivity, and good repeatability. It could detect only PRCoV, PRRSV, SIV, and PRV, without cross-reactions with TGEV, PEDV, PRoV, ASFV, FMDV, PCV2, PDCoV, and CSFV. The limits of detection (LODs) for PRCoV, PRRSV, SIV, and PRV were 129.594, 133.205, 139.791, and 136.600 copies/reaction, respectively. The intra-assay and inter-assay coefficients of variation (CVs) ranged from 0.29% to 1.89%. The established quadruplex RT-qPCR was used to test 4909 clinical specimens, which were collected in Guangxi Province, China, from July 2022 to September 2023. PRCoV, PRRSV, SIV, and PRV showed positivity rates of 1.36%, 10.17%, 4.87%, and 0.84%, respectively. In addition, the previously reported RT-qPCR was also used to test these specimens, and the agreement between these methods was higher than 99.43%. The established quadruplex RT-qPCR can accurately detect these four porcine respiratory viruses simultaneously, providing an accurate and reliable detection technique for clinical diagnosis.

The immunity protection of intestine induced by pseudorabies virus del gI/gE/TK in piglets

Compared to the classical strain of Pseudorabies virus (PRV), the PRV variant exhibits stronger transmissibility and pathogenicity, causing immense disasters for the global pig industry. Based on this variant, our laboratory has preliminarily constructed a modified pseudorabies virus with deletions in the gE/gI/TK genes. In this study, the protective efficacy of PRV XJ del gI/gE/TK against piglet intestinal damage was evaluated. The results demonstrated that piglets immunized with PRV XJ del gI/gE/TK exhibited alleviated intestinal damage caused by the PRV XJ variant strain. This included reduced viral load, suppressed inflammation, and maintenance of intestinal structure and function. Additionally, PRV XJ del gI/gE/TK also strongly activated the innate immune response in the intestines, increasing the expression of antiviral factor mRNA and the secretion of SIgA to counteract the attack of the PRV XJ variant strain. Our study indicates that PRV XJ del gI/gE/TK can inhibit intestinal damage caused by PRV XJ variant strain and activate the innate immune response in the intestines.

Epidemiological investigation, determination of related factors, and spatial-temporal cluster analysis of wild type pseudorabies virus seroprevalence in China during 2022

Introduction

Pseudorabies virus (PRV) is a linear DNA virus with a double-stranded structure, capable of infecting a diverse array of animal species, including humans. This study sought to ascertain the seroprevalence of Pseudorabies Virus (PRV) in China by conducting a comprehensive collection of blood samples from 16 provinces over the course of 2022.

Methods

The presence of PRV gE antibodies was detected through the utilization of an enzyme-linked immunosorbent assay (ELISA) technique. Logistic regression analysis was conducted to identify potential related factors associated with the serologic status of PRV gE at the animal level. Additionally, the SaTScan 10.1 software was used to analyze the spatial and temporal clusters of PRV gE seroprevalence.

Results

A comprehensive collection of 161,880 samples was conducted, encompassing 556 swine farms throughout the country. The analysis revealed that the seroprevalence of PRV gE antibodies was 12.36% (95% confidence interval [CI], 12.20% to 12.52%) at the individual animal level. However, at the swine farm level, the seroprevalence was considerably higher, reaching 46.22% (95% CI, 42.08% to 50.37%). Related factors for PRV infection at the farm level included the geographic distribution of farms and seasonal variables. Moreover, five distinct high seroprevalence clusters of PRV gE were identified across China, with the peak prevalence observed during the months of April through June 2022.

Conclusion

Our findings serve as a valuable addition to existing research on the seroprevalence, related factors, and temporal clustering of PRV gE in China. Furthermore, our study provides a reference point for the development of effective strategies for the prevention and control of pseudorabies and wild virus outbreaks.

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.

Global asymptotic stability in a pseudorabies virus model with age structure

Pseudorabies is a highly contagious disease caused by pseudorabies virus (PRV) or suid herpesvirus 1 (SuHV1), causing significant economic losses to the swine industry in countries where the disease exists. In this paper, we formulate an age structure model of pseudorabies virus that takes into account disease-related mortality and vertical transmission. We find a threshold to determine the stability and existence of the disease. We show that there is always a globally asymptotically stable boundary equilibrium if and only if R 02 < 1 + θ , which means that the disease always exists in piglets and will die out in adult pigs. When R 02 > 1 + θ , the boundary equilibrium is unstable and there exists a unique disease-endemic equilibrium, which is globally asymptotically stable. We give detailed proofs of our theoretical results and numerical examples. Brief concluding remarks are also provided.

Genomic Characterization and gE/gI-Deleted Strain Construction of Novel PRV Variants Isolated in Central China

Pseudorabies virus (PRV) variants have caused substantial economic losses in the swine industry in China since 2011. To surveil the genetic variation in PRV field strains, here, two novel variant strains of PRV were isolated from Shanxi Province in central China and were designated SX1910 and SX1911. To identify the genetic characteristics of the two isolates, their complete genomes were sequenced, and phylogenetic analysis and sequence alignment revealed that field PRV variants have undergone genetic variations; notably, the protein-coding sequences UL5, UL36, US1 and IE180 exhibited extensive variation and contained one or more hypervariable regions. Furthermore, we also found that the glycoproteins gB and gD of the two isolates had some novel amino acid (aa) mutations. Importantly, most of these mutations were located on the surface of the protein molecule, according to protein structure model analysis. We constructed a mutant virus of SX1911 with deletion of the gE and gI genes via CRISPR/Cas9. When tested in mice, SX1911-ΔgE/gI-vaccinated mice were protected within a comparable range to Bartha-K61-vaccinated mice. Additionally, a higher dose of inactivated Bartha-K61 protected the mice from lethal SX1911 challenge, while a lower neutralization titer, higher viral load and more severe microscopic lesions were displayed in Bartha-K61-vaccinated mice. These findings highlight the need for continuous monitoring of PRV and novel vaccine development or vaccination program design for PRV control in China.

Isolation and identification of two novel pseudorabies viruses with natural recombination or TK gene deletion in China

Pseudorabies virus (PRV), the causative agent of Aujeszky's disease, has gained increased attention in China in recent years due to outbreaks of emergent pseudorabies. However, there is limited information about the evolution and pathogenicity of emergent PRV field strains in China. In this study, two PRV field strains were isolated from an intensive pig farm with suspected PRV infection. These were named the GXLB-2015 and GXGG-2016 strains and their growth characteristics together with their genome sequences and pathogenicity were determined. Nucleotide homology and phylogenetic analysis revealed the GXLB-2015 stain was relatively close to the foreign PRV isolated strains with respect to the whole genome sequence. However, it formed an independent branch between the foreign PRV isolates and the previous PRV variants isolated in China. Further recombination and genetic evolution analysis showed that the GXLB-2015 strain was a natural recombinant between the Bartha strain and PRV variants. The GXGG-2016 strain was highly homologous with the Chinese classical strains, but it has a natural deletion of 69 aa in the thymidine kinase (TK) gene. Pathogenicity analysis showed that, the GXLB-2015 strain had the strongest pathogenicity to mice with an LD50 of 103.5, while the GXGG-2016 strain with the TK gene deletion was not pathogenic to mice. Taken together, our data provide direct evidence for the genomic recombination and natural TK gene deletion of PRVs, which may provide a reference for a better understanding of PRV evolution in China and contribute to the clinical control of PRV infection in pig farms.

Gallocatechin Gallate Inhibits the Replication of Pseudorabies Virus via Suppressing the Entry and Release Stages in Its Replication Cycle

The pseudorabies virus is a widespread swine pathogen that has caused significant economic losses to the global pig industry. Due to the emergence of PRV variant strains in recent years, vaccines cannot provide complete protection against the infection of PRV. Therefore, the research on antiviral compounds is of great importance for PRV treatment. In this study, an EGFP-labeled PRV was used to screen anti-PRV compounds from 86 natural product extracts. Gallocatechin gallate was found to efficiently inhibit the replication of PRV with a half-maximal inhibitory concentration (IC50) of 0.41 μM. In addition, it was found that gallocatechin gallate was unable to directly inactivate PRV and had no effect on the attachment stage of PRV. However, it was found that gallocatechin gallate significantly suppressed the viral entry stage. Furthermore, it was found that the release stage of PRV was also significantly suppressed by gallocatechin gallate. Together, this study found that gallocatechin gallate could efficiently inhibit the replication of PRV by suppressing the entry and release stages of PRV, which will contribute to the development of a new therapeutic strategy against PRV infection.

Recombinant Pseudorabies Virus Usage in Vaccine Development against Swine Infectious Disease

Pseudorabies virus (PRV) is the pathogen of pseudorabies (PR), which belongs to the alpha herpesvirus subfamily with a double stranded DNA genome encoding approximately 70 proteins. PRV has many non-essential regions for replication, has a strong capacity to accommodate foreign genes, and more areas for genetic modification. PRV is an ideal vaccine vector, and multivalent live virus-vectored vaccines can be developed using the gene-deleted PRV. The immune system continues to be stimulated by the gene-deleted PRVs and maintain a long immunity lasting more than 4 months. Here, we provide a brief overview of the biology of PRV, recombinant PRV construction methodology, the technology platform for efficiently constructing recombinant PRV, and the applications of recombinant PRV in vaccine development. This review summarizes the latest information on PRV usage in vaccine development against swine infectious diseases, and it offers novel perspectives for advancing preventive medicine through vaccinology.

Cytopathic and Genomic Characteristics of a Human-Originated Pseudorabies Virus

Pseudorabies virus (PRV) generally infects pigs and threatens the pig industry. However, recently we have isolated a PRV strain designated hSD-1/2019 from infected humans. In this study, we compared the complete genome sequence of hSD-1/2019 with those of pig-originated PRV strains. Sequence alignments revealed that the genome sequence of hSD-1/2019 was highly homologous to those of the porcine PRV strains. Phylogenetic analyses found that hSD-1/2019 was the closest related to porcine PRV endemic strains in China, particularly the variant strains circulating recently. We also showed that the glycoproteins important for the multiplication and pathogenesis of hSD-1/2019 were highly similar to those of the pig endemic strains. Diversifying selection analyses revealed that hSD-1/2019 and pig variant strains are under diversifying selection. Recombination analysis indicated that hSD-1/2019 was a recombinant of several PRV variant strains and an earlier PRV classic strain. Finally, we found that both human and pig-originated PRV strains could induce cytopathic effects in cells from humans, pigs, and mice, but only the human PRV and pig-variant PRV formed large syncytia in human cell lines. The data presented in this study contribute to our understanding of the molecular basis for the pathogenesis of human PRV from a genomic aspect.

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.

Establishment of an indirect ELISA method for antibody detection of porcine pseudorabies by recombinant gB, gC, and gD proteins

Pseudorabies virus (PRV), as a neuroherpes virus, leads to heavy economic losses in the pig industry worldwide. This study was designed to establish recombinant PRV glycoprotein B (gB), C, and D proteins as PRV diagnostic antigens. The gB/C, gC/D, and gB/C/D fusion sequences were synthesized and inserted into pET-28a⁺ vector to generate the recombinant plasmids. The identified positive recombinant plasmids were transformed into BL21 Escherichia coli. The results of the polymerase chain reaction and enzyme digestion showed that the gB/C, gC/D, and gB/C/D fusion proteins were successfully expressed. An indirect sandwich ELISA was developed with the gB/C, gC/D, and gB/C/D as coating antigens. The results of indirect enzyme-linked immunosorbent assay (ELISA) analysis of 184 PRV-positive porcine sera showed that the positive coincidence rates of three recombinant proteins ELISAs relative to IDEXX kit were 98.25%, 95.32%, and 98.83%, and the negative coincidence rates were 85.71%, 75% and 100%, respectively. The inter and intra batch repeatability tests showed that the coefficient of variations of our kits were all less than 5%. Especially, the gB/C/D-ELISA has the highest specificity and sensitivity among the ELISA methods developed in this study. We established a series expression system of gB/C, gC/D, and gB/C/D antigen epitope genes and Recombinant protein-based indirect ELISA, providing new ideas for PV diagnosis and vaccine development.

Investigation and analysis of etiology associated with porcine respiratory disease complex in China from 2017 to 2021

Porcine respiratory diseases complex (PRDC) is a highly serious threat to the pig industry. In the present study, we investigated and analyzed the etiology associated with PRDC and explored the role of viruses in respiratory bacterial infections. From 2017 to 2021, clinical samples were collected from 1,307 pigs with typical respiratory symptoms in 269 farms in China and screened for pathogens related to PRDC by PCR and bacterial isolation. The results indicated that PRRSV (41.16%, 95%CI: 38.49~43.83%), PCV2 (21.58%,95%CI: 19.35~23.81%), S. suis (63.50%, 95%CI: 60.89~66.11%), and G. parasuis (28.54%, 95%CI: 26.09~30.99%) were the most commonly detected pathogens in pigs with PRDC in China. The dominant epidemic serotypes (serogroups) of S. suis, G. parasuis, and P. multocida were serotype 2, serotype 1, and capsular serogroups D, respectively. Pigs of different ages exhibited different susceptibilities to these pathogens, e.g., PRRSV, PCV2, and G. parasuis had the highest detection rates in nursery pigs, whereas fattening pigs had the highest detection rates of P. multocida and A. pleuropneumoniae. Among the 1,307 pigs, the detection rates of S. suis, G. parasuis, P. multocida, and B. bronchiseptica were higher in virus-positive pigs, especially G. parasuis and P. multocida were significantly (p < 0.01) higher than in virus-negative pigs. In addition, a strong positive correlation was found between coinfection by PRRSV and G. parasuis (OR = 2.33, 95%CI: 1.12~2.14), PRRSV and P. multocida (OR = 1.55, 95%CI: 1.12~2.14), PCV2 and P. multocida (OR = 2.27, 95%CI: 1.33~3.87), PRRSV-PCV2 and S. suis (OR = 1.83, 95%CI: 1.29~2.60), PRRSV-PCV2 and G. parasuis (OR = 3.39, 95%CI: 2.42~4.74), and PRRSV-PCV2 and P. multocida (OR = 2.09, 95%CI: 1.46~3.00). In summary, PRRSV, PCV2, S. suis, and G. parasuis were the major pathogens in pigs with PRDC, and coinfections of two or more PRDC-related pathogens with strong positive correlations were common in China, such as PRRSV and G. parasuis, PRRSV and P. multocida, PCV2 and P. multocida, and also PRRSV-PCV2 and G. parasuis and PRRSV-PCV2 and P. multocida.

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.

The Epidemiology and Variation in Pseudorabies Virus: A Continuing Challenge to Pigs and Humans

Pseudorabies virus (PRV) can infect most mammals and is well known for causing substantial economic losses in the pig industry. In addition to pigs, PRV infection usually leads to severe itching, central nervous system dysfunction, and 100% mortality in its non-natural hosts. It should be noted that increasing human cases of PRV infection have been reported in China since 2017, and these patients have generally suffered from nervous system damage and even death. Here, we reviewed the current prevalence and variation in PRV worldwide as well as the PRV-caused infections in animals and humans, and briefly summarized the vaccines and diagnostic methods used for pseudorabies control. Most countries, including China, have control programs in place for pseudorabies in domestic pigs, and thus, the disease is on the decline; however, PRV is still globally epizootic and an important pathogen for pigs. In countries where pseudorabies in domestic pigs have already been eliminated, the risk of PRV transmission by infected wild animals should be estimated and prevented. As a member of the alphaherpesviruses, PRV showed protein-coding variation that was relatively higher than that of herpes simplex virus-1 (HSV-1) and varicella-zoster virus (VZV), and its evolution was mainly contributed to by the frequent recombination observed between different genotypes or within the clade. Recombination events have promoted the generation of new variants, such as the variant strains resulting in the outbreak of pseudorabies in pigs in China, 2011. There have been 25 cases of PRV infections in humans reported in China since 2017, and they were considered to be infected by PRV variant strains. Although PRV infections have been sporadically reported in humans, their causal association remains to be determined. This review provided the latest epidemiological information on PRV for the better understanding, prevention, and treatment of pseudorabies.

A Review of Pseudorabies Virus Variants: Genomics, Vaccination, Transmission, and Zoonotic Potential

Pseudorabies virus (PRV), the causative agent of Aujeszky’s disease, has a broad host range including most mammals and avian species. In 2011, a PRV variant emerged in many Bartha K61-vaccinated pig herds in China and has attracted more and more attention due to its serious threat to domestic and wild animals, and even human beings. The PRV variant has been spreading in China for more than 10 years, and considerable research progresses about its molecular biology, pathogenesis, transmission, and host–virus interactions have been made. This review is mainly organized into four sections including outbreak and genomic evolution characteristics of PRV variants, progresses of PRV variant vaccine development, the pathogenicity and transmission of PRV variants among different species of animals, and the zoonotic potential of PRV variants. Considering PRV has caused a huge economic loss of animals and is a potential threat to public health, it is necessary to extensively explore the mechanisms involved in its replication, pathogenesis, and transmission in order to ultimately eradicate it in China.

Isolation and Phylogenetic Analysis of Reemerging Pseudorabies Virus Within Pig Populations in Central China During 2012 to 2019

To understand the biological characteristics of the reemerging pseudorabies virus (PRV) strains, a total of 392 tissue samples were collected from diseased pigs during reemerging PR outbreaks between 2012 and 2019 on farms in central China where swine had been immunized with Bartha-K61 and 51 (13. 01%) were positive for the gE gene by PCR. Sixteen PRV strains were isolated and caused clinical symptoms and death in mice. Subsequently, gE, gC, gB, and gD complete genes were amplified from the 16 PRV isolates and sequenced. Phylogenetic analysis based on these four gene sequences shows that the 16 PRV isolates were more closely related to the Chinese PRV variants (after 2012) but genetically differed from early Chinese PRV isolates (before 2012). Sequence analysis reveals that PRV isolates exhibited amino acid insertions, substitutions, or deletions compared with early Chinese PRV isolates and European–American PRV strains. In addition, this is the first report that eight isolates (8/16) in this study harbor a unique amino acid substitution at position 280 (F to L) of the gC protein, and six isolates have an amino acid substitution at position 338 (A to V) of the gD protein compared with the Chinese PRV variants. The emulsion containing inactivated PRV NY isolate could provide complete protection against the NY isolate. This study might enrich our understanding of the evolution of reemerging PRV strains as well as pave the way for finding a model virus to develop a novel vaccine based on reemerging PRV strains.

Recombinant pseudorabies virus with gI/gE deletion generated by overlapping polymerase chain reaction and homologous recombination technology induces protection against the PRV variant PRV-GD2013

BACKGROUND

Since 2011, numerous highly virulent and antigenic variant viral strains have been reported in pigs that were vaccinated against the swine pseudorabies virus. These infections have led to substantial economic losses in the Chinese swine industry.

RESULTS

This study, constructed a novel recombinant vaccine strain with gI/gE deletion (PRV-GD2013-ΔgI/gE) by overlapping PCR and homologous recombination technology. The growth curves and plaque morphology of the recombinant virus were similar to those of the parental strain. However, PRV-GD2013-ΔgI/gE infection was significantly attenuated in mice compared with that of PRV-GD2013. Two-week-old piglets had normal rectal temperatures and displayed no clinical symptoms after being inoculated with 105 TCID50 PRV-GD2013-ΔgI/gE, indicating that the recombinant virus was avirulent in piglets. Piglets were immunized with different doses of PRV-GD2013-ΔgI/gE, or a single dose of Bartha-K61 or DMEM, and infected with PRV-GD2013 at 14 days post-vaccination. Piglets given high doses of PRV-GD2013-ΔgI/gE showed no obvious clinical symptoms, and their antibody levels were higher than those of other groups, indicating that the piglets were completely protected from PRV-GD2013.

CONCLUSIONS

The PRV-GD2013-ΔgI/gE vaccine strain could be effective for immunizing Chinese swine herds against the pseudorabies virus (PRV) strain.

Seroprevalence investigation and genetic analysis of pseudorabies virus within pig populations in Henan province of China during 2018-2019

In late 2011, the outbreak of pseudorabies (PR) occurred in Bartha-K61-vaccinated pig farms and spread rapidly to many provinces of China, causing substantial economic losses to the swine industry. A total of 4708 pig serum samples from Henan province during 2018-2019 were collected to screen for the presence of pseudorabies virus (PRV) gE-specific antibodies, and phylogenetic analysis based on the gE gene of PRV was performed. Of the 4708 serum samples tested, 30.14% (1419/4708) were seropositive for PRV antibodies, based on PRV gE-coated enzyme-linked immunosorbent assay (ELISA), with slaughterhouses having the highest seroprevalence. The seropositive rates of PRV also varied with the region and the season. Phylogenetic analysis showed that three PRV isolates from this study were clustered in an independent branch together with the Chinese variant PRV strains (after 2012), and had a closer genetic relationship with the Chinese variant PRV strains, but differed genetically from the 4 early Chinese PRV strains and 4 European-American strains. This study suggests that three PRV isolates may belong to PRV variants, and the development of a novel vaccine against PRV variants is particularly urgent.

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.

A novel human acute encephalitis caused by pseudorabies virus variant strain

BACKGROUND

Pseudorabies virus (PRV) is a common pathogen in multiple animal species particularly in pigs. However, PRV infection in humans is rare and to the best of knowledge, PRV has never been isolated from human cases before.

METHODS

Four acute encephalitis cases in humans were confirmed as PRV infection based on clinical symptoms, laboratory diagnosis, and metagenomic next-generation sequencing (mNGS). Cerebrospinal fluid (CSF) samples were collected and applied for virus isolation. Etiological and genetic characteristics of this PRV human isolate were further determined.

RESULTS

The patients manifested respiratory dysfunction and acute neurological symptoms. The mNGS revealed PRV specific nucleotide sequences in patients' CSF samples (7-6198 reads and 0.2446%-80.58% coverage). The PRV envelope glycoprotein B antibody, glycoprotein E antibody, and neutralizing antibody were positively detected. For the first time, a PRV strain, designated hSD-1/2019, was isolated and identified from one CSF sample, and transmission electron microscopy revealed hSD-1/2019 had typical morphology similar to swine PRV. Phylogenetic analysis illustrated that hSD-1/2019 was genetically closest to those PRV variant strains currently circulating in pigs in China, and this strain showed similar etiological characteristics to Chinese PRV variant strains, while different from Chinese classical strain. Moreover, hSD-1/2019 showed high pathogenicity and induced acute neurological symptoms in pigs.

CONCLUSIONS

A PRV strain was isolated from an acute human encephalitis case. This isolate showed close phylogenetic relationships and similar etiological characteristics to Chinese PRV variant strains, implying the great risk of PRV transmission from pigs to humans.

Antiviral Activity of Germacrone against Pseudorabies Virus in Vitro

Pseudorabies virus (PRV), a member of the Herpesviridae, is the causative agent of an acute infectious disease in a variety of animals. The emergence of a novel variant strain brought huge economic losses to the pig industry since classical vaccine strains were not completely effective against variant strains. Therefore, the development of new anti-pseudorabies virus drugs and vaccines is of great significance for the treatment and prevention of pseudorabies. In this study, we found that germacrone, one of the major components of the essential oils extracted from Rhizoma Curcuma, was able to effectively inhibit PRV replication in a dose-dependent manner in vitro. Germacrone showed antiviral activity against PRV in the early phase of the viral replication cycle. Moreover, we found that germacrone does not directly kill the virus, nor does it affect the expression of the PRV receptor protein nectin-1, nectin-2, and CD155. Our results suggest germacrone could be used as an efficient microbicide or immunomodulatory agent in the control of the emerging variant PRV.