Pseudorabies virus infection in mink: a host-specific pathogenesis

Additional Insertion of gC Gene Triggers Better Immune Efficacy of TK/gI/gE-Deleted Pseudorabies Virus in Mice

In recent years, pseudorabies virus (PRV) variants have resulted in an epidemic in swine herds and huge economic losses in China. Therefore, it is essential to develop an efficacious vaccine against the spread of PRV variants. Here, the triple-gene-deletion virus and the triple-gene-deletion plus gC virus were constructed by homologous recombination (HR). And then, their growth capacity, proliferation ability, and immune efficacy were evaluated. The results showed that the growth kinetics of the recombinant viruses were similar to those of the parental strain PRV-AH. Compared with the triple-gene-deletion virus group, the more dominant level of neutralizing antibody (NA) can be induced in the triple-gene-deletion plus gC virus group with the same 106.0 TCID50 dose after 4 and 6 weeks post-initial immunization (PII) (p < 0.0001). In addition, the antibody titers in mice immunized with the triple-gene-deletion plus gC virus were significantly higher than those immunized with triple-gene deletion virus with the same 105.0 TCID50 dose after 6 weeks PII (p < 0.001). More importantly, in the triple-gene-deletion plus gC virus group with 105.0 TCID50, the level of NA was close to that in the triple-gene deletion virus group with 106.0 TCID50 at 6 weeks PII. Meanwhile, the cytokines IL-4 and IFN-γ in sera were tested by enzyme-linked immunosorbent assay (ELISA) in each group. The highest level of IL-4 or IFN-γ was also elicited in the triple-gene deletion plus gC virus group at a dose of 106.0 TCID50. After challenge with PRV-AH, the survival rates of the triple-gene deletion plus gC virus immunized groups were higher than those of other groups. In immunized groups with 105.0 TCID50, the survival rate shows a significant difference between the triple-gene deletion plus gC virus group (75%, 6/8) and the triple-gene deletion virus group (12.5%, 1/8). In general, the immune efficacy of the PRV TK/gI/gE-deleted virus can be increased with additional gC insertion in mice, which has potential for developing an attenuated vaccine candidate for PRV control.

Isolation and Characterization of Yunnan Variants of the Pseudorabies Virus and Their Pathogenicity in Rats

Porcine pseudorabies has long existed in China and is a serious threat to the Chinese farming industry. To understand the prevalence and genetic variation of the porcine pseudorabies virus (PRV) and its pathogenicity in Yunnan Province, China, we collected 560 serum samples across seven Yunnan Province regions from 2020 to 2021 and detected anti-gE antibodies in these samples. Sixty-one clinical tissue samples were also collected from pigs with suspected PRV that were vaccinated with Bartha-K61. PRV-gE antibodies were found in 29.6% (166/560) of the serum samples. The PRV positivity rate in clinical tissue samples was 13.1% (8/61). Two isolates, PRV-KM and PRV-QJ, were obtained. The identity of the gB, gD, and gE genes between these isolates and the Chinese mutants exceeded 99.5%. These isolates and the classical Fa strain were used to infect 4-week-old rats intranasally to assess their pathogenicity. All infected rats showed the typical clinical and pathological features of PRV two days post-infection. The viral loads in the organs differed significantly among the infected groups. Viruses were detected in the saliva and feces at 12 h. Significant dynamic changes in total white blood cell counts (WBC), lymphocyte counts (Lym), and neutrophil counts (Gran) occurred in the blood of the infected groups at 24 and 48 h. These results show that mutant PRV strains are prevalent in Bartha-K61-vaccinated pigs in Yunnan Province, China. Moreover, rats shed PRV in their saliva and feces during early infection, indicating the need for rodent control in combatting PRV infections in Yunnan Province, China.

Pathogenicity and immunogenicity of a quadruple gene-deleted pseudorabies virus variant as a vaccine candidate

Since late 2011, the PRV variants have emerged in China, characterized by the increased virulence. The traditional attenuated vaccines have proven insufficient in providing complete protection, resulting in substantial economic losses to swine industry. In this study, a vaccine candidate strain, ZJ01-ΔgI/gE/TK/UL21, carrying the quadruple gene deletion was derived from the previously generated three gene-deleted virus ZJ01-ΔgI/gE/TK. As anticipated, piglets inoculated with ZJ01-ΔgI/gE/TK/UL21 exhibited normal body temperatures and showed no viral shedding, consistent with the observations from piglets treated with ZJ01-ΔgI/gE/TK. Importantly, a significant higher level of interferon induction was observed among piglets in the ZJ01-ΔgI/gE/TK/UL21 group compared to those in the ZJ01-ΔgI/gE/TK group. Upon challenge with the PRV variant ZJ01, piglets immunized with ZJ01-ΔgI/gE/TK/UL21 exhibited reduced viral shedding compared to the ZJ01-ΔgI/gE/TK group. Furthermore, piglets vaccinated with ZJ01-ΔgI/gE/TK/UL21 exhibited minimal pathological lesions in brain tissues, similar to those in the ZJ01-ΔgI/gE/TK group. These results underscore the potential of ZJ01-ΔgI/gE/TK/UL21 as a promising vaccine for controlling PRV infection.

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.

The prevention strategies of swine viruses related to xenotransplantation

Xenotransplantation is considered a solution for the shortage of organs, and pigs play an indispensable role as donors in xenotransplantation. The biosecurity of pigs, especially the zoonotic viruses carried by pigs, has attracted attention. This review introduces several viruses, including porcine endogenous retroviruses that are integrated into the pig genome in a DNA form, herpesviruses that have been proven to clearly affect recipient survival time in previous xenotransplant surgeries, the zoonotic hepatitis E virus, and the widely distributed porcine circoviruses. The detail virus information, such as structure, caused diseases, transmission pathways, and epidemiology was introduced in the current review. Diagnostic and control measures for these viruses, including detection sites and methods, vaccines, RNA interference, antiviral pigs, farm biosecurity, and drugs, are discussed. The challenges faced, including those posed by other viruses and newly emerged viruses, and the challenges brought by the modes of transmission of the viruses are also summarized.

HDAC6 Triggers the ATM-Dependent DNA Damage Response To Promote PRV Replication

Pseudorabies virus (PRV) infection is modulated by various cellular host factors. In this study, we investigated the role of histone deacetylase 6 (HDAC6) in this process. We determined HDAC6 expression in vitro and performed gene knockout, pharmacological inhibition analyses, immunofluorescence assays, and statistical analyses. We found that the pharmacological and genetic inhibition of HDAC6 significantly decreased PRV replication, whereas its overexpression promoted PRV replication. Additionally, we demonstrated that PRV infection can induce the phosphorylation of histone H2AX and lead to DNA damage response (DDR), and the ataxia telangiectasia mutated (ATM) inhibitor KU55933 inhibits DDR and PRV infection. Mechanistically, the HDAC6 inhibitor tubacin and HDAC6 knockout can decrease DDR. The results of this study suggested that HDAC6 may be a crucial factor in PRV-induced ATM-dependent DDR to promote PRV replication. IMPORTANCE Pseudorabies virus (PRV) is a member of the subfamily Alphaherpesvirinae of the family Herpesviridae. PRV infection in swine can lead to high morbidity and mortality of swine, causing huge economic losses. In particular, PRV variants can cause severe damage to the nervous and respiratory systems of humans, revealing that PRV may be a potential zoonotic pathogen. Vaccines for PRV have been developed that can delay or reduce the epidemic, but they currently cannot eliminate this disease completely. Therefore, studies should investigate new targets for the prevention and control of PRV infection. In this study, we demonstrated that HDAC6 can induce ataxia telangiectasia mutated-dependent DNA damage response to foster PRV replication, indicating that HDAC6 is a therapeutic target for PRV infection.

Archaic connectivity between the sulfated heparan sulfate and the herpesviruses - An evolutionary potential for cross-species interactions

The structural diversity of metazoic heparan sulfate (HS) composed of unique sulfated domains is remarkably preserved among various vertebrates and invertebrate species. Interestingly the sulfated moieties of HS have been known as the key determinants generating extraordinary ligand binding sites in the HS chain to regulate multiple biological functions and homeostasis. One such ligand for 3-O sulfation in the HS chain is a glycoprotein D (gD) from an ancient herpesvirus, herpes simplex virus (HSV). This interaction between gD and 3-O sulfated HS leads to virus-cell fusion to promote HSV entry. It is quite astonishing that HSV-1, which infects two-thirds of the world population, is also capable of causing severe diseases in primates and non-primates including primitive zebrafish. Supporting evidence that HSV may cross the species barrier comes from the fact that an enzymatic modification in HS encoded by 3-O sulfotransferase-3 (3-OST-3) from a vertebrate zoonotic species enhances HSV-1 infectivity. The latter phenomenon suggests the possible role of sulfated-HS as an entry receptor during reverse zoonosis, especially during an event when humans encounter domesticated animals in proximity. In this mini-review, we explore the possibility that structural diversity in HS may have played a substantial role in species-specific adaptability for herpesviruses in general including their potential role in promoting cross-species transmission.

Pseudorabies Virus Associations in Wild Animals: Review of Potential Reservoirs for Cross-Host Transmission

Pseudorabies virus (PRV) has received widespread attention for its potential health effects on humans, wildlife, domestic animals, and livestock. In this review, we focus on PRV dynamics in wildlife, given the importance of wild-origin PRV transmission to domestic and farm animals. Wild boars, pigs, and raccoons can serve as reservoirs of PRV, with viral transmission to domestic livestock occurring via several routes, such as wild herd exposure, contaminated meat consumption, and insect vector transmission. Many endangered feline and canine species can be infected with PRV, with acute disease and death within 48 h. The first confirmed human case of PRV infection in mainland China was reported in 2017. Thus, PRV exhibits potentially dangerous cross-host transmission, which is likely associated with inappropriate vaccination, poor awareness, and insufficient biosecurity. Currently, no vaccine provides full protection against PRV in all animals. Here, we summarize the epidemiology and pathogenesis of PRV infection in wild, domestic, and farmed animals, which may facilitate the design of novel therapeutics and strategies for controlling PRV infection and improving wildlife protection in China.

Serological Investigation and Genetic Characteristics of Pseudorabies Virus between 2019 and 2021 in Henan Province of China

In late 2011, severe pseudorabies (PR) outbreaks occurred among swine herds vaccinated with the Bartha-K61 vaccine in many provinces of China, causing enormous economic losses for the pork industry. To understand the epidemic profile and genetic characteristics of the pseudorabies virus (PRV), a total of 35,796 serum samples were collected from 1090 pig farms of different breeding scales between 2019 and 2021 in the Henan province where swine had been immunized with the Bartha-K61 vaccine, and PRV glycoprotein E (gE)-specific antibodies were detected using an enzyme-linked immunosorbent assay (ELISA). The results reveal that the overall positive rate for PRV gE antibodies was 20.33% (7276/35,796), which decreased from 25.00% (2596/10,385) in 2019 to 16.69% (2222/13,315) in 2021, demonstrating that PR still existed widely in pig herds in the Henan province but displayed a decreasing trend. Further analysis suggested that the PRV-seropositive rate may be associated with farm size, farm category, quarter, region and the cross-regional transportation of livestock. Moreover, the gE gene complete sequences of 18 PRV isolates were obtained, and they shared a high identity (97.1–100.0%) with reference strains at the nucleotide level. Interestingly, the phylogenetic analysis based on the gE complete sequences found that there were both classical strains and variant strains in pig herds. The deduced amino acid sequence analysis of the gE gene showed that there were unique amino acids in the classical strains, the variant strains and genotype Ⅱ strains. This study provides epidemiological data that could be useful in the prevention of pseudorabies in Henan, China, and this finding contributed to our understanding of the epidemiology and evolution of PRV.

The Role of Latency-Associated Transcripts in the Latent Infection of Pseudorabies Virus

Pseudorabies virus (PRV) can cause neurological, respiratory, and reproductive diseases in pigs and establish lifelong latent infection in the peripheral nervous system (PNS). Latent infection is a typical feature of PRV, which brings great difficulties to the prevention, control, and eradication of pseudorabies. The integral mechanism of latent infection is still unclear. Latency-associated transcripts (LAT) gene is the only transcriptional region during latent infection of PRV which plays the key role in regulating viral latent infection and inhibiting apoptosis. Here, we review the characteristics of PRV latent infection and the transcriptional characteristics of the LAT gene. We also analyzed the function of non-coding RNA (ncRNA) produced by the LAT gene and its importance in latent infection. Furthermore, we provided possible strategies to solve the problem of latent infection of virulent PRV strains in the host. In short, the detailed mechanism of PRV latent infection needs to be further studied and elucidated.

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.

Enhanced Immune Responses in Mice Induced by the c-di-GMP Adjuvanted Inactivated Vaccine for Pseudorabies Virus

Cyclic dimeric guanosine monophosphate (c-di-GMP) is a bacterial second messenger with immunomodulatory activities in mice, suggesting potential applications as a vaccine immunopotentiator or therapeutic agent. In this study, we evaluated the efficacy of c-di-GMP as an immunopotentiator for pseudorabies virus (PRV) inactivated vaccine in a murine model. We found that c-di-GMP improved the humoral and cellular immune responses induced by PRV inactivated vaccine and its effects on immunity reached the level comparable to that of a live attenuated vaccine. Furthermore, c-di-GMP enhanced the murine antibody response against the viral glycoprotein gB up to 120 days after immunization. The c-di-GMP–adjuvanted PRV inactivated vaccine induced long-term humoral immunity by promoting a potent T follicular helper cell response, which is known to directly control the magnitude of the germinal center B cell response. Furthermore, the c-di-GMP enhanced the response of bone marrow plasma cells and upregulated the expression of Bcl-2 and Mcl-1, which have been identified as anti-apoptotic regulatory genes of germinal center and memory B cells. Our findings open a new avenue for improving the immune efficacy of PRV inactivated vaccines.

Assessing the Risk of Commercial Vaccines Against Pseudorabies Virus in Cats

Pseudorabies virus (PRV) is a zoonotic agent that causes significant economic losses in animal husbandry worldwide, and gE-deleted vaccines play an important role in its treatment in the swine industry. However, the potential risk of attenuated PRV strains in commercial vaccines for other hosts remains unclear. Especially, cats are important companion animals for human beings. In this study, we investigated the prevalence and pathogenicity of the PRV wild strain in the cat population. We found that the occurrence of PR diseases in cats is sporadic, that the attenuated PRV strain causes slight clinical signs in cats, and that the virus is excreted 3 days post-infection. Our findings will be beneficial in furthering our understanding of the epidemiology and pathogenicity of PRV in cats and implying the great risk of RPV transmission from pigs to cats.

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.

Epidemiology of Porcine Pseudorabies from 2010 to 2018 in Tianjin, China

Pseudorabies (PR), the causative agent of Aujeszky's disease, has rapidly increased in recent years and has caused significant economic losses. To understand the seroprevalence and epidemiological characteristics of PR in Tianjin, China, a total of 23,627 blood and 1,093 tissue samples were collected from 228 pig farms during January 2010 to December 2018. The Pseudorabies virus (PRV) glycoprotein E (gE) antibody was tested by enzyme-linked immunosorbent assay (ELISA), and wild-type PRV (WT PRV) was detected by gE-polymerase chain reaction (PCR). Macroscopic and microscopic lesions were observed in tissue samples. The results showed that 46.70% of the serum samples and 49.76% of pig farms were seropositive for PRV gE antibody based on the ELISA results, and 13.54% of the tissue samples were positive for WT PRV detected by PCR. The positive rate of serum samples increased rapidly after 2011 and reached 62.40% in 2013. Although it gradually decreased from 2014 to 2018, the positive rate of serum samples remained at a high level. The positive rate of pig farms showed the same trend. Moreover, after 2011, the detection rate of WT PRV was increased rapidly and was significantly higher than in 2010 and 2011. Macroscopic and microscopic lesions were observed in various tissues during histopathological examination. Based on univariate analysis, the increased risk of seropositivity was associated with the immune status and infection in sows and fattening pigs. These findings demonstrate that PR was prevalent in the region of Tianjin, China. These epidemiological data can assist in the control of PR.

Tandem Mass Tag-Based Quantitative Proteomic Analysis of ISG15 Knockout PK15 Cells in Pseudorabies Virus Infection

Pseudorabies virus (PRV) is recognized as one of the most important pathogens of swine and poses a serious threat to the swine industry worldwide. Available commercial vaccines fail to protect against the emergence of new PRV strains. Therefore, the new protein targets against PRV highlight the urgent need for uncovering the molecular determinants of host cellular proteins following PRV infection. Interferon-stimulated gene 15 (ISG15) demonstrates an outstanding antiviral response. However, the molecular mechanism of ISG15 that affects PRV replication is incompletely known. Here, we performed a tandem mass tag (TMT)-based approach to quantitatively identify protein expression changes in PRV-infected ISG15 knockout PK15 (ISG15^−/−-PK15) cells. In total, 4958 proteins were identified by using TMT coupled with LC-MS/MS in this study. In the PRV- and mock-infected groups, 241 differentially expressed proteins (DEPs) were identified, 162 upregulated and 79 downregulated proteins at 24 h post-infection (hpi), among which AFP, Vtn, Hsp40, Herc5, and Mccc1 may play important roles in PRV propagation. To ensure the validity and reliability of the proteomics data, the randomly selected DEPs were verified by RT-qPCR and Western blot analysis, and the results were consistent with the TMT results. Bioinformatics analyses further demonstrated that the DEPs are mainly involved in various biological processes and signaling pathways, such as signal transduction, the digestive system, and the PI3K-AKT pathway. These findings may provide new insight into molecular mechanisms for PRV infection, which is helpful for identifying potential protein targets for antiviral agents.

Porcine Lymphotropic Herpesviruses (PLHVs) and Xenotranplantation

Porcine lymphotropic herpesviruses -1, -2 and -3 (PLHV-1, PLHV-2 and PLHV-3) are gammaherpesviruses which are widespread in pigs. They are closely related to the Epstein-Barr virus (EBV) and Kaposi sarcoma herpesvirus, both of which cause severe diseases in humans. PLHVs are also related to bovine and ovine gammaherpesviruses, which are apathogenic in the natural host, but cause severe diseases after transmission into other species. Until now, no association between PLHVs and any pig diseases had been described. However, PLHV-1 causes a post-transplantation lymphoproliferative disorder (PTLD) after experimental transplantations in minipigs. This disorder is similar to human PTLD, a serious complication of solid human organ transplantation linked to EBV. Xenotransplantation using pig cells, tissues and organs is under development in order to alleviate the shortage of human transplants. Meanwhile, remarkable survival times of pig xenotransplants in non-human primates have been achieved. In these preclinical trials, another pig herpesvirus, the porcine cytomegalovirus (PCMV), a roseolovirus, was shown to significantly reduce the survival time of pig xenotransplants in baboons and other non-human primates. Although PLHV-1 was found in genetically modified donor pigs used in preclinical xenotransplantation, it was, in contrast to PCMV, not transmitted to the recipient. Nevertheless, it seems important to use PLHV-free donor pigs in order to achieve safe xenotransplantation.

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.

Implication of the Identification of an Earlier Pseudorabies Virus (PRV) Strain HLJ-2013 to the Evolution of Chinese PRVs

Pseudorabies viruses (PRVs) pose a great threat to the pig industry of many countries around the world. Human infections with PRV have also been reported occasionally in China. Therefore, understanding the epidemiology and evolution of PRVs is of great importance for disease control in the pig populations and humans as well. In this study, we isolated a PRV designated HLJ-2013 from PRV-positive samples that had been collected in Heilongjiang, China, in 2013. The full genome sequence of the virus was determined to be ∼143 kbp in length using high-throughput sequencing. The genomic sequence identities between this isolate and 21 other previous PRV isolates ranged from 92.4% (with Bartha) to 97.3% (with SC). Phylogenetic analysis based on the full-length genome sequences revealed that PRV HLJ-2013 clustered together with all the Chinese strains in one group belonging to Genotype II, but this virus occurred phylogenetically earlier than all the other Chinese PRV strains. Phylogenetic trees based on both protein-coding genes and non-coding regions revealed that HLJ-2013 probably obtained its genome sequences from three origins: a yet unknown parent virus, the European viruses, and the same ancestor of all Chinese PRVs. Recombination analysis showed that HLJ-2013-like virus possibly donated the main framework of the genome of the Chinese PRVs. HLJ-2013 exhibited cytopathic and growth characteristics similar to that of the Chinese PRV strains SC and HeN1, but its pathogenicity in mice was higher than that of SC and lower than that of HeN1. The identification of HLJ-2013 takes us one step closer to understanding the origin of PRVs in China and provides new knowledge about the evolution of PRVs worldwide.

Retrospective detection and phylogenetic analysis of pseudorabies virus in dogs in China

Pseudorabies virus (PRV), the causative agent of Aujeszky's disease, has gained increased attention in China in recent years as a result of a recent outbreak of pseudorabies. The causative agent has a wide spectrum of hosts, including pigs, cattle, sheep, dogs, cats, bats, bears, and even some avian species. Although dog-related cases of pseudorabies have been reported regularly, many cases are overlooked, and few PRV strains are isolated because death occurs rapidly after PRV infection and veterinarians often do not test for PRV in dogs. Here, we performed a retrospective detection of PRV in dogs from July 2017 to December 2018. We found that PRV (including gE-deleted strains, classical strains, and variant strains) is prevalent in dogs regardless of season and region and that the epidemic PRV strains in dogs share high sequence similarity with gC and gE genes of swine epidemic strains and commercial vaccine strains. Collectively, our findings underscore the importance of PRV surveillance in dogs, which is beneficial for understanding the epidemiology of PRV in dogs and assists in efforts aimed at effectively controlling this disease.

Isolation and Characterization of a Variant Psedorabies Virus HNXY and Construction of rHNXY-∆TK/∆gE

The outbreak of pseudorabies in China, caused by more virulent pseudorabies virus (PRV) than the classical strains, has led to considerable economic losses. In this study, PRV strain HNXY was isolated from the Henan province of China in 2015 from the pig farm with severe reproductive failure in sows and a high mortality in piglets. The 50% tissue culture infectious doses (TCID50) of HNXY in Vero cells were examined to be 106.5/mL, and the neutralisation titer against Bartha-K61 was significantly higher than against HNXY when tested with the serum from Bartha-K61 vaccinated pigs. The 50% lethal doses (LD50) of HNXY to six-week-old BALB/c mice and two-month-old PRV-free pigs were both 102.3 TCID50. HNXY was classified as genotype II, and numerous amino acid variations were found in gB, gE, gC, gD, TK, and RR1 proteins, compared with PRV from other countries or those prevalent in China before 2012. The attenuated rHNXY-∆TK/∆gE was further constructed, which presented significantly smaller plaques than HNXY, as well as the similar growth kinetics. rHNXY-∆TK/∆gE was confirmed to be non-pathogenic to six-week-old BALB/c mice and zero-day-old piglets. This study isolated updated PRV promising to develop into a new vaccine candidate.

Host antiviral protein IFITM2 restricts pseudorabies virus replication

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Type I IFN and IFITMs showed marked upregulation following PRV infection in PK15 cells.

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IFITM proteins restricted PRV infection by interfering virus binding and entry.

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IFITM2-mediated inhibition of PRV entry requires the cholesterol pathway.

Pseudorabies virus (PRV) is one of the most destructive swine pathogens and leads to huge economic losses to the global pig industry. Type I interferons (IFNs) plays a pivotal role in the innate immune response to virus infection via induction of a series of interferon-stimulated genes (ISGs) expression. IFN-induced transmembrane (IFITM) proteins, a group of ISGs, are important host self-restriction factors, possessing a broad spectrum of antiviral effects. They are known confer resistance to a variety of RNA and DNA viruses. However, little is known about the role of IFITMs in PRV infection. In this study, we show that IFITM is crucial for controlling PRV infection and that IFITM proteins can interfere with PRV cell binding and entry. Furthermore, we showed that IFITM2-mediated inhibition of PRV entry requires the cholesterol pathway. Collectively, these results provide insight into the anti-PRV role of IFITM proteins and this inhibition possible associated with the change of cholesterol in the endosome, further underlying the importance of cholesterol in virus infection.

The Neuropathic Itch Caused by Pseudorabies Virus

Pseudorabies virus (PRV) is an alphaherpesvirus related to varicella-zoster virus (VZV) and herpes simplex virus type 1 (HSV1). PRV is the causative agent of Aujeskzy’s disease in swine. PRV infects mucosal epithelium and the peripheral nervous system (PNS) of its host where it can establish a quiescent, latent infection. While the natural host of PRV is the swine, a broad spectrum of mammals, including rodents, cats, dogs, and cattle can be infected. Since the nineteenth century, PRV infection is known to cause a severe acute neuropathy, the so called “mad itch” in non-natural hosts, but surprisingly not in swine. In the past, most scientific efforts have been directed to eradicating PRV from pig farms by the use of effective marker vaccines, but little attention has been given to the processes leading to the mad itch. The main objective of this review is to provide state-of-the-art information on the mechanisms governing PRV-induced neuropathic itch in non-natural hosts. We highlight similarities and key differences in the pathogenesis of PRV infections between non-natural hosts and pigs that might explain their distinctive clinical outcomes. Current knowledge on the neurobiology and possible explanations for the unstoppable itch experienced by PRV-infected animals is also reviewed. We summarize recent findings concerning PRV-induced neuroinflammatory responses in mice and address the relevance of this animal model to study other alphaherpesvirus-induced neuropathies, such as those observed for VZV infection.

Interspecies Transmission, Genetic Diversity, and Evolutionary Dynamics of Pseudorabies Virus

BACKGROUND

Pseudorabies virus (PRV) causes Aujeszky's disease in pigs and can be transmitted to other mammals, including humans. In the current study, we systematically studied the interspecies transmission and evolutionary history of PRV.

METHODS

We performed comprehensive analysis on the phylodynamics, selection, and structural biology to summarize the phylogenetic and adaptive evolution of PRV based on all available full-length and major glycoprotein sequences.

RESULTS

PRV can be divided into 2 main clades with frequent interclade and intraclade recombination. Clade 2.2 (variant PRV) is currently the most prevalent genotype worldwide, and most commonly involved in cross-species transmission events (including humans). We also found that the population size of clade 2.2 has increased since 2011, and the effective reproduction number was >1 from 2011 to 2016, indicating that PRV may be still circulating in swine herds and is still a risk in relation with cross-species transmission in China. Of note, we identified amino acid sites in some important glycoproteins gB, gC, gD, and gE that may be associated with PRV adaptation to new hosts and immune escape to vaccines.

CONCLUSIONS

Our study provides important genetic insight into the interspecies transmission and evolution of PRV within and between different hosts that warrant additional surveillance.

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.

Commercial vaccine against pseudorabies virus: A hidden health risk for dogs

Pseudorabies virus (PRV) is considered as an infectious agent with a wide of host range, causing considerable economic losses in animal husbandry. Although the commercial vaccine against PRV plays an critical role in control of this disease in swine industry, the potential risk of commercial vaccines against PRV for other host is unclear. Here, we report that the commercial vaccine against PRV is a hidden health risk for dogs. We found that different attenuated PRV strains in commercial vaccines possess different tissue tropism, and that the attenuated PRV strains are lethal to dogs, and that the attenuated PRV strain possesses the ability to spread horizontally among the dogs. Collectively, our findings provide clues that the commercial vaccine against PRV is a hidden risk for dogs, even for the owner of pet dogs to take seriously.

First detection and phylogenetic analysis of porcine circovirus type 2 in raccoon dogs

Background

Porcine circovirus type 2 (PCV2) is a major emerging virus of porcine circovirus-associated disease (PCVAD), which has brought huge economic losses to the global pig industry. Pigs are well known as the natural reservoir of PCV2. Recently, many researchers have revealed PCV2 could infect many other mammals like mice, calves, minks, dogs and goats. In 2018, our laboratory has admitted six cases of raccoon dogs from Qinhuangdao city of China, which were characterized by inappetence, lethargy, depression, abortion, and sterility.

Results

At last, six raccoon dog-origin PCV2 strains were isolated in this study. Pairwise-sequence comparisons demonstrated that the six raccoon dog-origin PCV2 strains shared a nucleotide similarity of 92.1–99.8% among 40 PCV2 representative strains. Phylogenetic analysis indicated these PCV2 isolates belonged to Chinese epidemic genotypes PCV2b and PCV2d. And aborted or sterile symptom was significantly associated with PCV2 infection in raccoon dogs by the chi-square test (χ² = 87.3, p < 0.001). The retrospective study revealed that raccoon dog-origin PCV2 strains shared 100% sequence similarity with the PCV2 stains isolated from pig farms around these raccoon dog farms, respectively.

Conclusion

In this study, the first supported evidence of PCV2 prevalence in raccoon dog farms of China was documented. PCV2 may be one of the most significant causative agents resulting in the reproductive failure of farmed raccoon dogs, implying that PCV2 could transmit from pigs to raccoon dogs. That indicated that PCV2 cross-species transmission will be a serious threat to China’s fur animal farming industry.

Low-pH Endocytic Entry of the Porcine Alphaherpesvirus Pseudorabies Virus

The alphaherpesvirus pseudorabies virus (PRV) is the causative agent of pseudorabies, a disease of great economic and welfare importance in swine. Other alphaherpesviruses, including herpes simplex virus (HSV), utilize low-pH-mediated endocytosis to enter a subset of cell types. We investigated whether PRV used this entry pathway in multiple laboratory model cell lines. Inhibition of receptor-mediated endocytosis by treatment with hypertonic medium prevented PRV entry. PRV entry into several cell lines, including porcine kidney (PK15) cells and African green monkey kidney (Vero) cells, was inhibited by noncytotoxic concentrations of the lysosomotropic agents ammonium chloride and monensin, which block the acidification of endosomes. Inactivation of virions by acid pretreatment is a hallmark of viruses that utilize a low-pH-mediated entry pathway. Exposure of PRV virions to pH 5.0 in the absence of host cell membranes reduced entry into PK15 and Vero cells by >80%. Together, these findings suggest that endocytosis followed by fusion with host membranes triggered by low endosomal pH is an important route of entry for PRV.IMPORTANCE PRV is a pathogen of great economic and animal welfare importance in many parts of the world. PRV causes neurological, respiratory, and reproductive disorders, often resulting in mortality of young and immunocompromised animals. Mortality, decreased production, and trade restrictions result in significant financial losses for the agricultural industry. Understanding the molecular mechanisms utilized by PRV to enter host cells is an important step in identifying novel strategies to prevent infection and spread. A thorough understanding of these mechanisms will contribute to a broader understanding of alphaherpesvirus entry. Here, we demonstrate PRV entry into multiple model cell lines via a low-pH endocytosis pathway. Together, these results provide a framework for elucidating the early events of the PRV replicative cycle.

A gD&gC-substituted pseudorabies virus vaccine strain provides complete clinical protection and is helpful to prevent virus shedding against challenge by a Chinese pseudorabies variant

Background

Since 2011, pseudorabies caused by a variant PRV has re-emerged in many Chinese Bartha-K61-vaccinated pig farms. An efficacious vaccine is necessary to control this disease. We described the construction of a gD&gC-substituted pseudorabies virus (PRV B-gD&gC^S) from the Bartha-K61 (as backbone) and AH02LA strain (as template for gD and gC genes) through bacterial artificial chromosome (BAC) technology using homologous recombination. The growth kinetics of PRV B-gD&gC^S was compared with Bartha-K61. Its safety was evaluated in 28-day-old piglets. Protection efficacy was tested in piglets by lethal challenge with AH02LA at 7 days post vaccination, including body temperature, clinical symptoms, virus shedding, mortality rate, and lung lesions.

Results

The results showed that a BAC clone of Bartha-K61 and a B-gD&gC^S clone were successfully generated. The growth kinetics of PRV B-gD&gC^S strain on ST (Swine testicular) cells was similar to that of the Bartha-K61 strain. No piglets inoculated intramuscularly with PRV B-gD&gC^S strain exhibited any clinical symptoms or virus shedding. After AH02LA challenge, all piglets in PRV B-gD&gC^S and Bartha-K61 groups (n = 5 each) survived without exhibiting any clinical symptoms and high body temperature. More importantly, PRV B-gD&gC^S strain completely prevented virus shedding in 2 piglets and reduced virus shedding post challenge in the other 3 piglets as compared with Bartha-K61 group.

Conclusions

Our results suggest that PRV B-gD&gC^S strain is a promising vaccine candidate for the effective control of current severe epidemic pseudorabies in China.

First detection and genetic analysis of fox-origin porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is a causative agent of porcine circovirus-associated disease (PCVAD), which is a serious problem in the swine industry worldwide. In recent years, nonporcine-origin PCV2 has attracted more and more attention of the researchers. This study reported on the first identification of PCV2 in farmed foxes with reproductive failure. Three fox-origin PCV2 strains were successfully isolated, sequenced, and designated as FoxHB1, FoxHB2, and FoxHB3 respectively. Pairwise-sequence comparisons of the complete genomes revealed that three fox-origin PCV2 strains had nucleotide identities varied from 91.9% to 99.7% with representative strains of PCV2 different genotypes. Meanwhile, phylogenetic analysis based on complete genomes of 44 PCV2 strains indicated that the fox-origin PCV2 strains belonged to Chinese epidemic genotypes PCV2b and PCV2d. These results provided the first supported evidence that PCV2 could infect foxes, implying that the cross-species transmission of PCV2 would be a big threat to Chinese fur animal-bearing industry.

Characterization of a moderately pathogenic pseudorabies virus variant isolated in China, 2014

In this study, we reported a moderately pathogenic pseudorabies virus (PRV) variant isolated from one Bartha-K61-vaccinated pig farm in Weifang, Shandong Province, China, 2014. The sick piglets in the farm were characterized by anorexia, weight loss and neurologic symptoms but did not die. Sequence alignment of the gE gene indicated that it belonged to a new mutated PRV strain and about 15% amino acid sites had mutations, deficiencies and insertions compared to the other PRV strains. The gD gene had two amino acid insertions and ten amino acid mutations in comparison with the Bartha-K61 vaccine strain. The TK and gM genes were the same as one highly pathogenic PRV TJ strain. Evidence from virus isolation, laboratory challenge, serological detection and histopathologic examination confirmed that the etiological agent of the disease is PRV SD1404, which is a moderately pathogenic strain and causes piglets to be sick but not to die. PRV SD1404 strain is different from other reports and should be paid more attention to avoid economic losses.

How Host Specific Are Herpesviruses? Lessons from Herpesviruses Infecting Wild and Endangered Mammals

Herpesviruses are ubiquitous and can cause disease in all classes of vertebrates but also in animals of lower taxa, including molluscs. It is generally accepted that herpesviruses are primarily species specific, although a species can be infected by different herpesviruses. Species specificity is thought to result from host-virus coevolutionary processes over the long term. Even with this general concept in mind, investigators have recognized interspecies transmission of several members of the Herpesviridae family, often with fatal outcomes in non-definitive hosts-that is, animals that have no or only a limited role in virus transmission. We here summarize herpesvirus infections in wild mammals that in many cases are endangered, in both natural and captive settings. Some infections result from herpesviruses that are endemic in the species that is primarily affected, and some result from herpesviruses that cause fatal disease after infection of non-definitive hosts. We discuss the challenges of such infections in several endangered species in the absence of efficient immunization or therapeutic options.

Genetic characterization and mutation analysis of Qihe547 Aujeszky's disease virus in China

BACKGROUND

Aujeszky's disease virus (ADV) can cause neurologic disease in young pigs, respiratory disease in older pigs and abortion or birth of mummified fetuses or stillborn neonates. The re-emergence of Aujeszky's disease (AD) in pig farms vaccinated with live vaccine (Bartha-K61) caused substantial economic losses to Chinese pig industry since late 2011. A field ADV, named Qihe547, was isolated from pigs that exhibited suspected AD clinical symptoms. To better understand the genetic characteristics and mutations of Qihe547 ADV, the whole genome was sequenced and analyzed.

RESULTS

The genomic length of Qihe547 ADV was 143,404 bp, with 73.59% G + C contents. Phylogenetic analysis based on the whole genome of ADV strains revealed that Chinese ADV strains were located to one group with three subgroups. Qihe547 ADV was closely related to these novel ADV strains isolated in China since 2012. Qihe547 presented numerous hypervariable regions compared with oversea ADV strains. In 34 genes of Qihe547 ADV, amino acid (AA) insertion or deletion were observed. In addition, numerous AA mutations were found in the main protective antigen genes (gB, gC and gD genes). The differences of potential antigenic peptides in the main protective antigens between Qihe547 ADV and ADV Bartha were discovered in the dominant antigenic regions of gB (AA59-AA126, AA507-AA734),the extracellular region of gC and gD.

CONCLUSION

High diversity was observed between Qihe547 and foreign ADV isolates. The AA variations and the differences of potential antigenic peptides in the important functional regions of the main protective antigen (gB, gC and gD) of ADV Qihe547 may contribute to immune evasion of the virus and may be partial reason that the virus escapes from the vaccination of Bartha-K61 vaccine. In a word, the effect of the variations obviously requires further research.

Epidemiological investigation of pseudorabies in Shandong Province from 2013 to 2016

In late 2011, a variant pseudorabies virus (vPRV) emerged in Bartha-K61-vaccinated pig herds, resulting in high morbidity and mortality of piglets in China. Since 2013, the autopsy lesions, histological examinations, virus isolation, phylogenetic analysis and selection pressure analysis of the gE gene of vPRV were recorded for 395 clinical cases, and 5,033 pig serum samples were detected by PRV gE-coated enzyme-linked immunosorbent assay. The major clinical symptoms were abortion in pregnant sows, fatal neurological signs in piglets and respiratory disease in growing pigs. Necrotic splenitis, hepatitis and lymphadenitis, haemorrhagic nephritis and non-suppurative encephalitis were observed by histopathological examination. Typical eosinophilic inclusion bodies were found in the nuclei of liver cells. Using PCR, 110 samples among 395 clinical cases tested positive for the gE gene. Fifteen vPRV strains were isolated and confirmed by sequencing and phylogenetic analysis of the gE gene. The strains shared 97.1%-99.9% nucleotide (nt) and 96.6%-99.5% amino acid (aa) homology with PRV reference strains. Selection pressure analysis showed that one site in the codons of glycoprotein E was under positive selection. Of the 5,033 serum samples, 2,909 were positive by ELISA for a positive rate of 57.8%. These results showed that vPRV was still prevalent in Shandong Province, indicating severe PRV infectious pressure. The preparation of new vaccines against PRV is extremely urgent.

Vaccine resistant pseudorabies virus causes mink infection in China

Background

Pseudorabies, a highly contagious infectious disease of swine is caused by pseudorabies virus (PRV). PRV can cause fatal infection in other animal species.

Results

We report a deadly outbreak of pseudorabies that killed 87.2% (3522/4028) minks in a farm in 2014 in Shandong Province, China. PRV was isolated by using Vero cell culture and detected in mink samples by PCR from minks died during the outbreak. Epidemiological analysis indicated that 5.8% of minks (33/566) were PCR positive to PRV in Shandong Province. Phylogenetic analysis indicated that the PRV strains isolated from minks in this study were in the same clade with the Chinese porcine PRV isolates, which are resistant to the PRV vaccine.

Conclusions

We demonstrated that pseudorabies virus caused an outbreak of minks in a farm in Shandong Province of China and the virus has a very high infection rate in minks in Shandong Province, which is a challenge for the fur industry in China.

Pathogenicity and Whole Genome Sequence Analysis of a Pseudorabies Virus Strain FJ-2012 Isolated from Fujian, Southern China

The outbreaks of pseudorabies have been frequently reported in Bartha-K61-vaccinated farms in China since 2011. To study the pathogenicity and evolution of the circulating pseudorabies viruses in Fujian Province, mainland China, we isolated and sequenced the whole genome of a wild-type pseudorabies virus strain named "FJ-2012." We then conducted a few downstream bioinformatics analyses including phylogenetic analysis and pathogenic analysis and used the virus to infect 6 pseudorabies virus-free piglets. FJ-2012-infected piglets developed symptoms like high body temperature and central nervous system disorders and had high mortality rate. In addition, we identified typical micropathological changes such as multiple gross lesions in infected piglets through pathological analysis and conclude that the FJ-2012 genome is significantly different from known pseudorabies viruses, in which insertions, deletions, and substitutions are observed in multiple immune and virulence genes. In summary, this study shed lights on the molecular basis of the prevalence and pathology of the pseudorabies virus strain FJ-2012. The genome of FJ-2012 could be used as a reference to study the evolution of pseudorabies viruses, which is critical to the vaccine development of new emerging pseudorabies viruses.

iTRAQ-based Proteomic Analysis of Porcine Kidney Epithelial PK15 cells Infected with Pseudorabies virus

Pseudorabies virus (PRV) is one of the most important pathogens of swine, resulting in severe economic losses to the pig industry. To improve our understanding of the host responses to PRV infection, we applied isobaric tags for relative and absolute quantification (iTRAQ) labeling coupled with liquid chromatography-tandem mass spectrometry to quantitatively identify the differentially expressed cellular proteins in PRV-infected PK15 cells. In total, relative quantitative data were identified for 4333 proteins in PRV and mock- infected PK15 cells, among which 466 cellular proteins were differentially expressed, including 234 upregulated proteins and 232 downregulated proteins. Bioinformatics analysis disclosed that most of these differentially expressed proteins were involved in metabolic processes, cellular growth and proliferation, endoplasmic reticulum (ER) stress response, cell adhesion and cytoskeleton. Moreover, expression levels of four representative proteins, beta-catenin, STAT1, GRB2 and PCNA, were further confirmed by western blot analysis. This is the first attempt to analyze the protein profile of PRV-infected PK15 cells using iTRAQ technology, and our findings may provide valuable information to help understand the host response to PRV infection.

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.

Pseudorabies virus infection (Aujeszky's disease) in an Iberian lynx (Lynx pardinus) in Spain: a case report

Background

The only natural hosts of Pseudorabies virus (PRV) are members of the family Suidae (Sus scrofa scrofa). In species other than suids infection is normally fatal. In these mammals, including carnivores, PRV typically causes serious neurologic disease. The endangered Iberian lynx (Lynx pardinus) is a wild feline endemic to south-western Europe (Iberian Peninsula). The Iberian lynx was found to be the world’s most endangered felid species in 2002. In wild felines, PRV infection has only been previously reported once in a Florida panther in 1994. No seropositive lynxes have ever been found, nor has PRV been detected in dead Iberian lynxes to date.

Case presentation

We describe the first reported case of pseudorabies in an Iberian lynx (Lynx pardinus). Pseudorabies was diagnosed in a young wild Iberian lynx from Extremadura (SW Spain) by histopathological examination, immunohistochemistry, polymerase chain reaction (PCR) and sequence analysis. Gross lesions included alopecia of the ventral neck, bloody gastro-intestinal contents and congestion of the brain. Histopathological analysis showed a moderate nonsuppurative meningoencephalitis with diffuse areas of demyelination, necrotizing gastritis and enteritis of the small intestine. Pseudorabies virus (PRV) antigen was found in neuronal and non-neuronal cells of the brain, tonsils, and gastric glandular epithelial cells by immunohistochemical analysis. The presence of the virus in the brain was confirmed by nested PCR. The sequence analysis of the 146 bp fragment (from the viral glycoprotein B gene) showed that the amplified sequence matched (with 100% identity) the PRV genome. Furthermore, specific DNA from glycoprotein D and E encoding-genes was detected by conventional and real-time PCR, respectively, confirming the latter that this infection was produced by a wild-type PRV strain.

Conclusions

This study supports the suspicion that PRV could infect the Iberian lynx. The detection of PRV in a dead Iberian lynx suggests that the virus may have a negative impact on the survival of endangered lynxes in the wild. However, because this is the first verified instance of lynx mortality resulting from pseudorabies, its true impact on the population is unknown.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0938-7) contains supplementary material, which is available to authorized users.

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.

Development of an immunochromatographic strip for antibody detection of pseudorabies virus in swine

An immunochromatographic strip was developed for the serological detection of pseudorabies virus (PRV) in swine. In the strip, the expressed protein of gB, one of the glycoproteins of PRV, labeled with colloidal gold, was used as the detector; staphylococcal protein A and swine anti-pseudorabies virus antibody were blotted on nitrocellulose membrane for the test and control lines, respectively. The specificity of the strip was 98.1%, and the sensitivity of the strip with reference anti-PRV serum was 96.0%. Swine serum samples (296) were collected to evaluate the characteristics of the strip in comparison with an existing commercial kit. The agreement was 93.6%. Furthermore, the dipstick assay based on the strip is rapid (5 min) and easy to perform with no requirement of professional skills, reagents, or equipment. This suggests that the immunochromatographic strip is an acceptable alternative for use in clinical laboratories lacking specialized equipment and for field diagnosis.

Emergence of a Pseudorabies virus variant with increased virulence to piglets

Pseudorabies virus (PRV) causes Pseudorabies (PR), an economically important disease in domestic swine. PR outbreaks on pig farms caused by PRV variant strains in Bartha-K61-vaccinated pigs have resulted in considerable economic losses in China since 2011. In this study, the pathogenicity of the PRV variant JS-2012 strain to pigs was investigated by experimentally inoculating piglets of different ages in comparison with a classic virulent PRV SC strain. The JS-2012 strain caused an earlier onset of clinical signs and higher mortality in 15, 30, and 60-day-old pigs, as compared with a classic virulent PRV SC strain. The Bartha-K61 vaccination provided complete protection against challenge with classical virulent PRV, but only partial protection against challenge with the JS-2012 strain in piglets. In conclusion, the increased virulence of the PRV variant may have partly contributed to the PR outbreak in China.

Characterization of monoclonal antibodies that recognize the amino- and carboxy-terminal epitopes of the pseudorabies virus UL42 protein

The pseudorabies virus (PRV) UL42 protein, known as the DNA polymerase processivity factor, is an essential protein required for viral replication. The in vitro function of UL42 has been characterized; however, there is little information concerning the linear B cell epitopes of UL42 that are recognized during humoral immune responses. We generated and characterized six UL42-reactive monoclonal antibodies (mAbs) from mice that had been immunized with a recombinant form of UL42. Through western blotting analysis, we identified two regions of UL42 (amino acids 39-148 and 302-384) that reacted with these mAbs. We then synthesized a panel of UL42-derived peptides spanning the two regions and screened the six mAbs. We were able to identify three linear epitopes ((116)SGGVLDALK(124), (354)KRPAAPR(360), and (360)RMYTPIAK(367)) by enzyme-linked immunosorbent assays. The (116)SGGVLDALK(124) epitope was located at the amino-terminus, while the other two epitopes were at the carboxy-terminus. Using these mAbs, we found that UL42 localized to the nucleus during viral replication and could be immunoprecipitated from PRV-infected PK-15 cells. We also established a UL42 mAb-based immunoperoxidase monolayer assay for the determination of PRV titers. Sequence analysis showed that the linear epitopes of UL42 were highly conserved among PRV strains. Taken together, our results indicate that the six generated mAbs could be useful tools for investigating the structure and function of UL42 during viral replication. In addition, these mAbs could be applied to diagnostic and therapeutic approaches for the effective control of PRV infections.

Pathogenesis of natural and experimental Pseudorabies virus infections in dogs

BACKGROUND

Since late 2011, cases of suspected canine pseudorabies have increased in north China with the outbreak of swine pseudorabies in the same area, but the pathogenesis of canine Pseudorabies virus (PRV) infections in China is poorly understood. In this study, we investigated the pathogenesis of canine pseudorabies.

METHODS

The pathological changes in 13 dogs that died of natural PRV infections (confirmed by pathogen detection) during 2011-2013 in Beijing were evaluated. An experimental study was also conducted in which healthy adult beagle dogs were administered PRV isolate BJ-YT by subcutaneous injection. The dog tissues were subjected to gross and microscopic examinations and immunohistochemical analysis and the dogs' serum cardiac troponin-I (cTn-I) was measured.

RESULTS

Systemic hemorrhage and/or congestion were the most marked pathological changes in both the naturally and experimentally PRV-infected dogs. Macroscopically, the major lesions consisted of petechiae and ecchymoses in both the endocardium and epicardium, thrombi in the mitral valves, hemorrhage in the lungs and thymus, and incomplete contraction of the spleen. Microscopically, the major histopathological findings were systemic hemorrhage and congestion, nonsuppurative ganglioneuritis (in the experimentally infected dogs, unexamined in the naturally PRV-infected dogs), brainstem encephalitis (in the naturally infected dogs), necrosis or exudation in the myocardium, and lymphoid depletion in many lymphoid organs and tissues. Viral antigens were only detected in the brainstems and peripheral ganglia of the infected dogs. Serum cTn-I was significantly higher in the experimentally PRV-infected dogs with myocardial lesions than in the dogs without myocardial lesions.

CONCLUSIONS

Based on these results, we conclude that virally induced systemic hemorrhage, peripheral nervous system pathology, and/or cardiac injury can individually or collectively cause death in PRV-infected dogs. The respiratory signs of the disease are attributed to cardiogenic lesions.

Pathogenic pseudorabies virus, China, 2012

In 2012, an unprecedented large-scale outbreak of disease in pigs in China caused great economic losses to the swine industry. Isolates from pseudorabies virus epidemics in swine herds were characterized. Evidence confirmed that the pathogenic pseudorabies virus was the etiologic agent of this epidemic.

A novel gE-deleted pseudorabies virus (PRV) provides rapid and complete protection from lethal challenge with the PRV variant emerging in Bartha-K61-vaccinated swine population in China

The currently used Bartha-K61 strain is a very safe and effective vaccine against pseudorabies (PR) and has played a critical role in the control and eradication of PR worldwide. Since late 2011, however, PR reemerged among Bartha-K61-vaccinated pig population in many regions in China. Our previous studies demonstrated that the Bartha-K61 vaccine was unable to provide complete protection from the challenge with the PRV TJ strain (PRVTJ), a representative emerging PRV variant that was isolated from a Bartha-K61-immunized pig farm in Tianjin, China. Here, we generated a gE-deleted PRV, named as rPRVTJ-delgE, based on PRVTJ and evaluated its safety and immunogenicity in pigs. Our results showed that groups of piglets (n=5) immunized with 10(3), 10(4) or 10(5)TCID50 rPRVTJ-delgE did not exhibit clinical signs following immunization and challenge and were protected clinically and virologically from the lethal challenge with PRVTJ as early as 1 week post-immunization, in contrast with the incomplete protection provided by the Bartha-K61 vaccine. These indicate that rPRVTJ-delgE is a promising candidate vaccine for updating Bartha-K61 for the control of the currently epidemic PR in China.

Emergence of virulent pseudorabies virus infection in northern China

Our investigation was conducted in order to verify a recent severe epidemic at several swine farms in northern China that indicated a newly emerging disease. Evidence confirmed that the epidemic was caused by a virulent Pseudorabies virus infection in swine herds.

Herpesviruses--a zoonotic threat?

Herpesviruses are highly host specific and share a long synchronous evolution with their hosts. Only in rare cases, species barriers fall and allow animal to human or human to animal transmission. Among the zoonotic herpesviruses, Cercopithecine herpesvirus 1 is the most significant and can be transmitted from macaques to human. Conversely, Human herpesvirus 1 is capable of causing severe disease in primates. Besides those two examples, there are several herpesviruses with a certainly limited or only suspected ability to cross species barriers. Those include Saimiriine herpesvirus 2, Phocid herpesvirus 2, Equid herpesvirus 1, Epstein-Barr Virus, Marek's disease virus, and Pseudorabies virus. Concerning xenotransplantations, porcine gammaherpesviruses must be considered as a zoonotic threat.

Validation of immuno-laser capture microdissection coupled with quantitative RT-PCR to probe blood-brain barrier gene expression in situ

Laser capture microdissection (LCM) holds great potential for analyzing gene expression profiles in situ. Most recently, this laboratory employed a novel immunostain-based LCM protocol (immuno-LCM) to selectively retrieve brain microvascular endothelial cells (BMEC) from intimately associated perivascular cells. However, before this protocol can be confidently coupled to downstream analytical platforms, it must be demonstrated that any variability associated with it is minimal, so as not to obscure data interpretation. As various factors could contribute to variability, this study focused on determining whether technical inconsistency and/or biological diversity of sample populations, played such a role. Specifically, two separate immuno-LCM-derived BMEC samples derived from adjacent tissue sections of a single mouse (to detect only technical variability), and from analogous tissue sections of three different mice (to detect technical and biological variability) were compared for their relative expression of 16 genes, using quantitative-RT-PCR (qRT-PCR). Both significant linear and rank-order correlations were observed between different sections from the same animal, underscoring lack of technical variability in this LCM application. Furthermore, a three-dimensional scatter plot of gene expression profiles from the three animals was linear, and ANOVA showed absence of statistically significant differences between any of the animals, confirming lack of biological variability. These findings argue that immuno-LCM coupled to qRT-PCR affords a reproducible means to assay gene expression in situ.