Eradication Of Pseudorabies Virus Research Articles

Establishment of pseudorabies virus latency and reactivation model in mice dorsal root ganglia culture.

Pseudorabies virus (PRV) belongs to the alpha herpesvirus family and is responsible for Aujeszky's disease in pigs. Similar to other alpha herpesviruses, PRV establishes a lifelong latent infection in trigeminal ganglion. These latently infected pigs serve as a reservoir for recurrent infections when reactivation is triggered, making the eradication of PRV a challenging task. However, the molecular mechanism underlying PRV latency and reactivation in neurons is still poorly understood due to limitations in the in vitro model. To establish a pseudorabies virus latency and reactivation model in primary neuron cultures, we isolated dorsal root ganglion (DRG) from newborn Kunming mice using a method named epineurium-pulling for DRG collection (EPDC) and cultured primary neurons in vitro. A dual-colour recombinant PRV BAC mRuby-VP16 was constructed and 0.5 multiplicity of infection (MOI) was found as an appropriate dose in the presence of aciclovir to establish latency. Reactivation was induced using UV-inactivated herpesviruses or a series of chemical inhibitors. Interestingly, we found that not only UV-PRV, but also UV-HSV-1 and UV-BHoV-5 were able to induce rapid PRV reactivation. The efficiency of reactivation for LY294002, forskolin, etoposide, dexamethasone, and acetylcholine was found to be dependent on their concentration. In conclusion, we developed a valuable model of PRV latency and reactivation, which provides a basis for future mechanism research.

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.

A Comparison of Pseudorabies Virus Latency to Other α-Herpesvirinae Subfamily Members.

Pseudorabies virus (PRV), the causative agent of Aujeszky’s disease, is one of the most important infectious pathogens threatening the global pig industry. Like other members of alphaherpesviruses, PRV establishes a lifelong latent infection and occasionally reactivates from latency after stress stimulus in infected pigs. Latent infected pigs can then serve as the source of recurrent infection, which is one of the difficulties for PRV eradication. Virus latency refers to the retention of viral complete genomes without production of infectious progeny virus; however, following stress stimulus, the virus can be reactivated into lytic infection, which is known as the latency-reactivation cycle. Recently, several research have indicated that alphaherpesvirus latency and reactivation is regulated by a complex interplay between virus, neurons, and the immune system. However, with those limited reports, the relevant advances in PRV latency are lagging behind. Therefore, in this review we focus on the regulatory mechanisms in PRV latency via summarizing the progress of PRV itself and that of other alphaherpesviruses, which will improve our understanding in the underlying mechanism of PRV latency and help design novel therapeutic strategies to control PRV latency.

The Attenuated Pseudorabies Virus Vaccine Strain Bartha Hyperactivates Plasmacytoid Dendritic Cells by Generating Large Amounts of Cell-Free Virus in Infected Epithelial Cells.

Pseudorabies virus (PRV) is a porcine alphaherpesvirus and the causative agent of Aujeszky's disease. Successful eradication campaigns against PRV have largely relied on the use of potent PRV vaccines. The live attenuated Bartha strain, which was produced by serial passaging in cell culture, represents one of the hallmark PRV vaccines. Despite the robust protection elicited by Bartha vaccination, very little is known about the immunogenicity of the Bartha strain. Previously, we showed that Bartha-infected epithelial cells trigger plasmacytoid dendritic cells (pDC) to produce much higher levels of type I interferons than cells infected with wild-type PRV. Here, we show that this Bartha-induced pDC hyperactivation extends to other important cytokines, including interleukin-12/23 (IL-12/23) and tumor necrosis factor alpha (TNF-α) but not IL-6. Moreover, Bartha-induced pDC hyperactivation was found to be due to the strongly increased production of extracellular infectious virus (heavy particles [H-particles]) early in infection of epithelial cells, which correlated with a reduced production of noninfectious light particles (L-particles). The Bartha genome is marked by a large deletion in the US region affecting the genes encoding US7 (gI), US8 (gE), US9, and US2. The deletion of the US2 and gE/gI genes was found to be responsible for the observed increase in extracellular virus production by infected epithelial cells and the resulting increased pDC activation. The deletion of gE/gI also suppressed L-particle production. In conclusion, the deletion of US2 and gE/gI in the genome of the PRV vaccine strain Bartha results in the enhanced production of extracellular infectious virus in infected epithelial cells and concomitantly leads to the hyperactivation of pDC. IMPORTANCE The pseudorabies virus (PRV) vaccine strain Bartha has been and still is critical in the eradication of PRV in numerous countries. However, little is known about how this vaccine strain interacts with host cells and the host immune system. Here, we report the surprising observation that Bartha-infected epithelial porcine cells rapidly produce increased amounts of extracellular infectious virus compared to wild-type PRV-infected cells, which in turn potently stimulate porcine plasmacytoid dendritic cells (pDC). We found that this phenotype depends on the deletion of the genes encoding US2 and gE/gI. We also found that Bartha-infected cells secrete fewer pDC-inhibiting light particles (L-particles), which appears to be caused mainly by the deletion of the genes encoding gE/gI. These data generate novel insights into the interaction of the successful Bartha vaccine with epithelial cells and pDC and may therefore contribute to the development of vaccines against other (alphaherpes)viruses.

The Attenuated Pseudorabies Virus Vaccine Strain Bartha K61: A Brief Review on the Knowledge Gathered During 60 Years of Research.

Pseudorabies virus (PRV) is a member of the alphaherpesvirus subfamily of the herpesviruses and is the causative agent of Aujeszky’s disease in pigs, causing respiratory, neurological, and reproductive symptoms. Given the heavy economic losses associated with Aujeszky’s disease epidemics, great efforts were made to develop efficacious vaccines. One of the best modified live vaccines to this day is the attenuated Bartha K61 strain. The use of this vaccine in extensive vaccination programs worldwide has assisted considerably in the eradication of PRV from the domesticated pig population in numerous countries. The Bartha K61 strain was described in 1961 by Adorján Bartha in Budapest and was obtained by serial passaging in different cell cultures. Ever since, it has been intensively studied by several research groups, for example, to explore its efficacy as a vaccine strain, to molecularly and mechanistically explain its attenuation, and to use it as a retrograde neuronal tracer and as a vector vaccine. Given that the Bartha K61 vaccine strain celebrates its 60th birthday in 2021 with no sign of retirement, this review provides a short summary of the knowledge on its origin, characteristics, and use as a molecular tool and as a vaccine.

Serosurvey for Pseudorabies (Aujeszky's Disease) in Free-Range Wild Boars (Sus scrofa) of Brazil.

Free-ranging wild boars (Sus scrofa) from two different Brazilian biomes were sampled. Only one of 36 (2.8%) animals tested from central-western Brazil were positive for antibodies against pseudorabies virus (PRV) by enzyme-linked immunosorbent assay. Peccaries and other wildlife species can be exposed to PRV in these areas. In addition, wild boars could have impact on livestock and PRV eradication.

Pseudorabies virus in North-West Italian wild boar (Sus scrofa) populations: prevalence and risk factors to support a territorial risk-based surveillance.

Although the eradication of Pseudorabies virus (PrV) in domestic pigs is ongoing, the circulation of this virus in wild boars remains a threat in the currently unprotected, 'low prevalence', pig population. In this study, we reported PrV prevalence data and the influence of possible risk factors in 2 North-West Italian wild boar populations (free and enclosed) with the goal of supporting the implementation of a risk-based AD surveillance system. Sera from 1,425 wild boars were collected between 2011 and 2015 and tested by ELISA for the presence of PrV antibodies; the overall raw seroprevalence was 30.39% (433/1,425; CI 95% 28.01-32.85%). A significant difference was however observed between the prevalence rates of the free range population (9.98%; 90/902; CI 95%; 8.10-12.12%) and the enclosed population of La Mandria park (Piedmont, Italy) (65.58%; 343/523; CI 95%; 61.51-69.65%). In both populations a significantly higher number of adults and females were found positive to PrV ELISA. Specific territorial data on PrV circulation in wild boars should be acquired from other regions for guiding risk-based measures in order to reduce the threat of AD re-infection in a more cost-effective manner.

Molecular epidemiology of pseudorabies virus in Yunnan and the sequence analysis of its gD gene.

Outbreaks of pseudorabies (PRs) have occurred in Yunnan, China, which caused significant economic loss. To determine the prevalence and origin of PR in Yunnan, especially among vaccinated pigs, overall 791 samples of blood, tissue, semen, and sera were analyzed by serological methods, PCR, and sequence analysis of gD gene. Detection with viral gI antibody or PCR showed that the yearly positive rates of PR virus (PRV) in Yunnan from 2010 to 2014 were 48.15, 21.26, 2.17, 5.22, and 0.35%, respectively, with an average of 15.43%. In general, the incidence declined through the period of 2010-2014 probably due to the application of PRV eradication strategies. A phylogenetic tree was constructed based on the complete sequence of gD gene, with all strains clustered into two independent clades, i.e., Asian and European-American clades. The virus isolates from Henan, Tianjin, Heilongjiang, Sichuan, Shandong, Fujian, Xinjiang, Hubei, Guangdong, and Yunnan fell into Asian group, which harbored South Korea isolate. Four Yunnan virus isolates together with South Korean Namyangju fell into in the European-American clade. It showed that PR was pandemic as there was not a clear clue about the geographical origin of the PRV isolates in China since 2010.

Aujeszky's disease and the effects of infection on Japanese swine herd productivity: a cross-sectional study.

Pseudorabies virus (PRV) is endemic in some regions of Japan. We investigated the effects of PRV infection status on herd productivity. Serum samples were obtained from 48 swine herds in Japan. Within each herd, three serum samples were obtained from growing pigs at four different ages, as well as from sows in low and high parity groups. Sera were tested for antibodies against wild-type PRV via competitive ELISA. Herds were classified into PRV positive and negative groups based on serological results. Herds infected with PRV exhibited postweaning mortalities (6.84%) that were significantly (P=0.0018) higher than those in unaffected herds (4.73%). Because of the reduced productivity in PRV positive herds, the current PRV eradication program must be strengthened.

Pseudorabies Virus Variant in Bartha-K61–Vaccinated Pigs, China, 2012

The widely used pseudorabies virus (PRV) Bartha-K61 vaccine has played a key role in the eradication of PRV. Since late 2011, however, a disease characterized by neurologic symptoms and a high number of deaths among newborn piglets has occurred among Bartha-K61–vaccinated pigs on many farms in China. Clinical samples from pigs on 15 farms in 6 provinces were examined. The PRV gE gene was detectable by PCR in all samples, and sequence analysis of the gE gene showed that all isolates belonged to a relatively independent cluster and contained 2 amino acid insertions. A PRV (named HeN1) was isolated and caused transitional fever in pigs. In protection assays, Bartha-K61 vaccine provided 100% protection against lethal challenge with SC (a classical PRV) but only 50% protection against 4 challenges with strain HeN1. The findings suggest that Bartha-K61 vaccine does not provide effective protection against PRV HeN1 infection.

An analysis of a presumed major outbreak of pseudorabies virus in a vaccinated sow herd

We describe a major outbreak of pseudorabies virus (PRV) in a sow herd in which the sows were vaccinated simultaneously three times a year with a vaccine containing Bartha strain. Also in the associated rearing herd in which the gilts were vaccinated twice an outbreak of PRV occurred. The outbreak was analysed with mathematical models, statistical methods and Monte-Carlo simulation. Under the assumption that the outbreak started with one introduction of virus the reproduction ratio R(ind)--as a measure of transmission of PRV between individuals--in the sow herd was estimated with a Generalized Linear Model to be 1.6. Also under the assumption of one introduction of virus R(ind) in the rearing herd was estimated with a martingale estimator to be 1.7. Both estimates were significantly larger than 1. Mathematical analysis showed that heterogeneity in the sow herd, because of the presence of not-optimally immunized replacement sows could not be the only cause of the observed outbreak in the sow herd. With Monte-Carlo simulations, the duration of an outbreak after a single introduction of virus and R(ind) = 1.6 did not mimic the data and thus the hypothesis of a single introduction with R(ind) = 1.6 could also be rejected and R(ind) is thus, not necessarily above 1. Moreover, with statistical analysis, endemicity in the combination of herds as a cause for the observed outbreak could be rejected. Endemicity in the rearing herd alone could not be excluded. Therefore, multiple introductions from outside and most probably from the rearing herd were possibly the cause of the observed outbreak(s). The implications for eradication of pseudorabies virus were discussed.

Comparison of two pseudorabies virus vaccines, that differ in capacity to reduce virus excretion after a challenge infection, in their capacity of reducing transmission of pseudorabies virus

Pseudorabies virus (PRV) vaccines are often compared for their capacity to reduce virus excretion after a challenge infection. Vaccines, used for the eradication of PRV, however, should reduce transmission of PRV among pigs. The purpose of this study was to investigate whether the amount of virus excreted after a challenge infection is an accurate measure of the capacity of a vaccine to reduce transmission of PRV among pigs. Two experiments were carried out, each using two groups of 10 pigs. The pigs in group one were intramuscularly vaccinated once with the glycoprotein E (gE)-negative vaccine X, the pigs in group two with the gE-negative strain 783. Eight weeks later, 5 pigs in each group were inoculated with wild-type PRV. A gE-ELISA was used to detect PRV infection. The transmission of PRV was estimated from the number of contact infections and expressed as the reproduction ratio R. The inoculated pigs vaccinated with vaccine X shed significantly more virus than the inoculated pigs vaccinated with strain 783. However, despite the difference in virus excretion, the transmission of PRV between the two groups did not differ. We conclude that virus excretion is not an accurate measure for determining vaccine effectiveness. However, R of vaccine X ( R = 0.98) was not significantly below one, whereas R of vaccine 783 ( R = 0) was significantly below one. Consequently, we cannot exclude the possibility that major outbreaks of PRV occur among pigs vaccinated with vaccine X.

Benefit-cost analysis of the national Pseudorabies virus eradication program

Summary An epidemiologic model of Pseudorabies virus (PRV) in swine was developed. This model was used to project future herd-to-herd disease transmission under alternative eradication or control programs over 20 years (1993 to 2012). With current PRV eradication program funding, it was projected that prevalence would be 23% in higher-risk states in the United States, 10% in moderate-risk states, and 1% in lower-risk states. Increased funding for the PRV eradication program was projected to reduce PRV prevalence substantially. Productivity and economic impacts of PRV also were estimated for the average size farrow-to-finish operation. These impacts included mortality for preweaning, nursery, growing/finishing, and breeding hogs; market weights and number of market hogs sold; farrowing rates, number of live pigs per litter, and number of litters per sow-year. Profitability was estimated to be $6/cwt less for PRV-in-fected herds than for uninfected herds. Aggregate effects of PRV eradication programs were estimated by use of economic welfare analysis. For all PRV eradication program alternatives analyzed, consumers were the major beneficiaries of the program because of reduced prices and increased consumption of pork. Estimates of the value of economic welfare impacts under the current program with an assumed parallel supply-curve shift were determined: consumers gained $336.5 million; producers gained $35.9 million; government expenditures were $197.1 million; and the benefit/cost ratio of the program was 1.89. Economic welfare measures were projected to increase substantially with increased PRV eradication program funding. Economic welfare measures also were estimated under other assumptions.

Pseudorabies virus eradication by area-wide vaccination is feasible.

This article reviews the rationale for using marker vaccines and companion diagnostic tests in the eradication of pseudorabies virus (PRV). Recent advances in vaccinology and epidemiology indicate that, despite the inability to induce complete immunity, vaccination is a useful tool in the battle against PRV. This review focuses on the effectiveness of vaccination under field conditions and on herd, management and regional factors that are associated with PRV introduction or transmission.

Eradication of pseudorabies virus from three large swine herds achieved by management intervention and use of a vaccine with a deletion for glycoprotein I

Summary Three large farrow-to-finish swine herds in Illinois, quarantined because of injection with pseudorabies virus (prv), were enrolled in an intensified prv eradication program, with the goal being release from quarantine within 3 years. The intervention plan primarily relied on vaccination, using a vaccine with a deletion of the genes coding for glycoprotein I, in breeding and growing/finishing pigs and decreases of movement and mixing of growing/finishing pigs. The initial goal was to decrease viral spread in the growing/finishing pigs, thereby enabling production of seronegative replacement gilts. Off-site rearing of replacement gilts was implemented in 1 recently infected herd in which the seroprevalence in the growing/finishing group was high. Results of bimonthly serologic monitoring indicated that there was minimal spread of prv in the growing/finishing pigs after 1 year. Increases in the number of sows culled combined with an increase in the number of seronegative replacement gilts entering the breeding group resulted in a reduction of sow seroprevalence, so that phased test and removal of seropositive breeding stock could commence in all 3 herds at about 18 months after initiation of the program. Persistent use of the test-and-removal procedure and repeated testing for release from quarantine were required for the most recently infected herd. All herds were released from quarantine within 3 years, indicating that a prv eradication program based on vaccination and management changes designed to minimize the spread of prv can be used in conjunction with test-and-removal procedures to effectively eliminate prv from large farrow-to-finish swine herds.

Glycoprotein E of pseudorabies virus and homologous proteins in other alphaherpesvirinae.

This paper reviews biological properties of glycoprotein E (gE) of pseudorabies virus (Aujeszky's disease virus) and homologous proteins in other alphaherpesvirinae. It focuses on the gene encoding gE, conserved regions in the gE protein and its homologs, the complex of gE and gI, biological functions of gE in vitro and in vivo, the role of gE in latency and the role of gE in the induction of humoral and cellular immune responses. Special emphasis is placed on the use of gE as a marker protein in the control and eradication of pseudorabies virus.

Evaluation of the sensitivity and specificity of two diagnostic tests for antibodies to pseudorabies virus glycoprotein X.

The diagnostic performance of 2 enzyme-linked immunosorbent assays (gX-T, gX-H) for antibodies to pseudorabies virus (PRV) glycoprotein X (gX) were evaluated using 311 serum samples from a nonvaccinated quarantined herd. When the standardized virus neutralization (VN) test, which uses the Shope strain (VN Shope), was used as the comparative diagnostic standard, the gX-T test had a 7% false-negative rate and a 52% false-positive rate, and the gX-H test had a 19% false-negative rate and a 19% false-positive rate. When the VN test with a Bartha recombinant strain (VN Bartha gIIIKa) was used as the diagnostic standard, the gX-T test had a 9% false-negative rate and a 26% false-positive rate, and the gX-H test had a 24% false-negative rate and a 11% false-positive rate. Thus, the gX-T test was more sensitive and the gX-H test was more specific. Additional diagnostic tests on 79 serum samples from a noninfected herd did not produce false positives for the gX-H test, but there was an 8% false-positive rate for the gX-T test. Previous studies from our laboratory have demonstrated that VN Bartha gIIIKa has higher sensitivity than VN Shope, without losing specificity, and thus is a better comparative diagnostic standard. When adding a suspect range to the gX-T test, using the same criteria as the suspect range for the gX-H test, the false-positive rate of the gX-T test was reduced to 5% when evaluated versus VN Bartha gIIIKa in the infected herd and to 1% for the PRV-negative herd.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk factors associated with the seroprevalence of pseudorabies virus in Illinois swine herds

Risk factors for the seroprevalence of pseudorabies virus (PRV) were evaluated for 499 swine herds in Illinois (USA) diagnosed as PRV-infected. The outcome analyzed was the PRV seroprevalence rate for a herd, as determined from serum-neutralization testing conducted during a 180-day period around the time that the herd PRV eradication plan was developed (120 days before to 60 days after). Primary risk factors tested by multiple linear regression analysis were herd size, farrow-to-finish operation, degree of confinement, age at weaning, all-in/all-out pig flow, and density of infected herds in the geographical region. Vaccination, calendar date when eradication plan was developed, and time from quarantine until development of herd plan were included as model covariates. PRV seroprevalence increased with increasing geographical density of infected herds, and was higher with total confinement. In addition, PRV seroprevalence was higher in vaccinated herds, increased over the course of the eradication program, and decreased with an increased time between quarantine and the development of a herd plan.