Construction and immune response characterization of a recombinant pseudorabies virus co-expressing capsid precursor protein (P1) and a multiepitope peptide of foot-and-mouth disease virus in swine

Advances in molecular epidemiology and detection methods of pseudorabies virus

Pseudorabies (PR), a highly contagious disease caused by the pseudorabies virus (PRV), represents a significant threat to the global swine industry. Despite the success of developed countries in controlling the PRV epidemic through swine pseudorabies eradication programs, wild boars, as a potential source of infection, still require sustained attention and effective control measures. Concurrently, there has been considerable global attention directed towards cases of PRV infection in humans. In consideration of the aforementioned factors, this paper presents a comprehensive review of recent developments in the PRV genome, epidemiology, vaccine research, and molecular detection methods. The epidemiology section presents an analysis of the transmission routes, susceptible animal groups, and geographic distribution of PRV, as well as an examination of the trend of the epidemic in recent years. In the field of vaccine research, the current development of genetically engineered vaccines is emphasized, and the immunogenicity and safety of vaccines are discussed. Moreover, the molecular detection techniques utilized to identify PRV, including immunological methods, nucleic acid detection methods, biosensors, and so forth, are presented in a systematic manner. Finally, this paper presents a comprehensive discussion of the current status of PRV-related research and offers insights into future directions, with the aim of providing a foundation for the scientific prevention and control of PRV.

The Development of Classical Swine Fever Marker Vaccines in Recent Years

Classical swine fever (CSF) is a severe disease that has caused serious economic losses for the global pig industry and is widely prevalent worldwide. In recent decades, CSF has been effectively controlled through compulsory vaccination with a live CSF vaccine (C strain). It has been successfully eradicated in some countries or regions. However, the re-emergence of CSF in Japan and Romania, where it had been eradicated, has brought increased attention to the disease. Because the traditional C-strain vaccine cannot distinguish between vaccinated and infected animals (DIVA), this makes it difficult to fight CSF. The emergence of marker vaccines is considered to be an effective strategy for the decontamination of CSF. This paper summarizes the progress of the new CSF marker vaccine and provides a detailed overview of the vaccine design ideas and immunization effects. It also provides a methodology for the development of a new generation of vaccines for CSF and vaccine development for other significant epidemics.

Generation and Immunogenicity of a Recombinant Pseudorabies Virus Co-Expressing Classical Swine Fever Virus E2 Protein and Porcine Circovirus Type 2 Capsid Protein Based on Fosmid Library Platform

Pseudorabies (PR), classical swine fever (CSF), and porcine circovirus type 2 (PCV2)-associated disease (PCVAD) are economically important infectious diseases of pigs. Co-infections of these diseases often occur in the field, posing significant threat to the swine industry worldwide. gE/gI/TK-gene-deleted vaccines are safe and capable of providing full protection against PR. Classical swine fever virus (CSFV) E2 glycoprotein is mainly used in the development of CSF vaccines. PCV2 capsid (Cap) protein is the major antigen targeted for developing PCV2 subunit vaccines. Multivalent vaccines, and especially virus-vectored vaccines expressing foreign proteins, are attractive strategies to fight co-infections for various swine diseases. The gene-deleted pseudorabies virus (PRV) can be used to develop promising and economical multivalent live virus-vectored vaccines. Herein, we constructed a gE/gI/TK-gene-deleted PRV co-expressing E2 of CSFV and Cap of PCV2 by fosmid library platform established for PRV, and the expression of E2 and Cap proteins was confirmed using immunofluorescence assay and western blotting. The recombinant virus propagated in porcine kidney 15 (PK-15) cells for 20 passages was genetically stable. The evaluation results in rabbits and pigs demonstrate that rPRVTJ-delgE/gI/TK-E2-Cap elicited detectable anti-PRV antibodies, but not anti-PCV2 or anti-CSFV antibodies. These findings provide insights that rPRVTJ-delgE/gI/TK-E2-Cap needs to be optimally engineered as a promising trivalent vaccine candidate against PRV, PCV2 and CSFV co-infections in future.

Utilization of herpesviridae as recombinant viral vectors in vaccine development against animal pathogens

Throughout the past few decades, numerous viral species have been generated as vaccine vectors. Every viral vector has its own distinct characteristics. For example, the family herpesviridae encompasses several viruses that have medical and veterinary importance. Attenuated herpesviruses are developed as vectors to convey heterologous immunogens targeting several serious and crucial pathogens. Some of these vectors have already been licensed for use in the veterinary field. One of their prominent features is their capability to accommodate large amount of foreign DNA, and to stimulate both cell-mediated and humoral immune responses. A better understanding of vector-host interaction builds up a robust foundation for the future development of herpesviruses-based vectors. At the time, many molecular tools are applied to enable the generation of herpesvirus-based recombinant vaccine vectors such as BAC technology, homologous and two-step en passant mutagenesis, codon optimization, and the CRISPR/Cas9 system. This review article highlights the most important techniques applied in constructing recombinant herpesviruses vectors, advantages and disadvantages of each recombinant herpesvirus vector, and the most recent research regarding their use to control major animal diseases.

Generation and Efficacy Evaluation of a Recombinant Pseudorabies Virus Variant Expressing the E2 Protein of Classical Swine Fever Virus in Pigs

Classical swine fever (CSF) is an economically important infectious disease of pigs caused by classical swine fever virus (CSFV). Pseudorabies (PR), which is caused by pseudorabies virus (PRV), is another important infectious disease of pigs and other animals. Coinfections of pigs with PRV and CSFV occur occasionally in the field. The modified live vaccine Bartha-K61 strain has played an important role in the control of PR in many countries, including China. Since late 2011, however, increasing PR outbreaks caused by an emerging PRV variant have been reported in Bartha-K61-vaccinated swine populations on many farms in China. Previously, we generated a gE/gI-deleted PRV (rPRVTJ-delgE) based on this PRV variant, which was shown to be safe and can provide rapid and complete protection against lethal challenge with the PRV variant in pigs. Here, we generated a new recombinant PRV variant expressing the E2 gene of CSFV (rPRVTJ-delgE/gI-E2) and evaluated its immunogenicity and efficacy in pigs. The results showed that rPRVTJ-delgE/gI-E2 was safe for pigs, induced detectable anti-PRV and anti-CSFV neutralizing antibodies, and provided complete protection against the lethal challenge with either the PRV TJ strain or the CSFV Shimen strain. The data indicate that rPRVTJ-delgE/gI-E2 is a promising candidate bivalent vaccine against PRV and CSFV coinfections.

Recombinant pseudorabies virus expressing P12A and 3C of FMDV can partially protect piglets against FMDV challenge

One of the crucial factors for evaluation of an effective genetically engineered vaccine is whether susceptible animals are protected from virus challenge after vaccination. In this study, a recombinant pseudorabies virus (PRV-P12A3C) that expressed capsid precursor polypeptide P12A and nonstructural protein 3C of foot-and-mouth disease virus (FMDV) was used as a vaccine. The expression of P12A3C and its immunogenicity and protective efficacy against FMDV challenge were measured. Humoral and cellular immune responses were evaluated after each immunization. Subsequently, each piglet was challenged with 1000 ID(50) (50% infection dose) FMDV serotype O, named OR/80, which is used to produce vaccine in China. PRV-P12A3C induced a high level of neutralizing antibody and FMDV-specific lymphocytes. Inactivated vaccine provided 100% protection, and the vector strain (TK(-)/gE(-)/gI(-)) showed no protection. PRV-P12A3C induced 60% protection, compared with piglets that were vaccinated with TK(-)/gE(-)/gI(-). The severity of clinical signs for the remaining two piglets was lighter and the appearance of vesicles was delayed.

Promising multiple-epitope recombinant vaccine against foot-and-mouth disease virus type O in swine

In order to develop a completely safe immunogen to replace the traditional inactivated vaccine, a tandem-repeat multiple-epitope recombinant vaccine against foot-and-mouth disease (FMD) virus (FMDV) type O was developed. It contained three copies each of residues 141 to 160 and 200 to 213 of VP1 of the O/China/99 strain of FMDV coupled with a swine immunoglobulin G heavy-chain constant region (scIgG). The data showed that the multiple-epitope recombinant vaccine elicited high titers of anti-FMDV specific antibodies in swine at 30 days postvaccination (dpv) and conferred complete protection against a challenge with 10³ 50% swine infective doses of the O/China/99 strain. The anti-FMDV specific antibody titers were not significantly different between the multiple-epitope recombinant vaccine and the traditional vaccine (t test, P > 0.05). The number of 50% pig protective doses was 6.47, which is higher than the number recommended by the World Organization for Animal Health. The multiple-epitope recombinant vaccine resulted in a duration of immunity of at least 6 months. We speculate that the multiple-epitope recombinant vaccine is a promising vaccine that may replace the traditional inactivated vaccine for the prevention and control of FMD in swine in the future.

Development and immunogenicity of a recombinant pseudorabies virus expressing Sj26GST and SjFABP from Schistosoma japonicum

Recombinant pseudorabies virus (PRV) Bartha-K61 vaccine strains expressing Schistosoma japonicum 26kDa glutathione S-transferase (Sj26GST) and fatty acid binding protein (SjFABP), designated as rPRV/Sj26GST, rPRV/SjFABP and rPRV/Sj26GST-SjFABP, were constructed and evaluated for their ability to protect mice and sheep against S. japonicum challenge. Animals were given 2 intramuscular immunizations 3 weeks apart, and challenged with S. japonicum cercariae 4 weeks later. All mice vaccinated with recombinant virus developed specific anti-SWAP (soluble worm antigen preparation) antibody, splenocyte proliferative response and production of IFN-gamma and IL-2. Injection of rPRV/Sj26GST-SjFABP significantly increased levels of antibody, splenocyte proliferative response and production of IFN-gamma, compared with rPRV/Sj26GST and rPRV/SjFABP. These recombinant viruses have been shown to be safe for sheep. Challenge experiments showed worms and egg burdens were significantly reduced in animals immunized with recombinant PRVs. Most importantly, rPRV/Sj26GST-SjFABP dramatically enhanced protection with worm reduction and hepatic reduction of 39.3% and 45.5% respectively in mice, and 48.5% and 51.2% in sheep, while rPRV/Sj26GST and rPRV/SjFABP provided corresponding protection of only up to 23.7% and 27.2% in mice, and 29.0% and 35.5% in sheep. These results indicate that the multivalent vaccine for S. japonicum can produce significant specific immunity and protection, and that PRV Bartha-K61 is an effective live vector for an animal schistosomiasis japonica vaccine.

Targeting the porcine immune system--particulate vaccines in the 21st century

During the last decade, the propagation of immunological knowledge describing the critical role of dendritic cells (DC) in the induction of efficacious immune responses has promoted research and development of vaccines systematically targeting DC. Based on the promise for the rational design of vaccine platforms, the current review will provide an update on particle-based vaccines of both viral and synthetic origin, giving examples of recombinant virus carriers such as adenoviruses and biodegradable particulate carriers. The viral carriers carry pathogen-associated molecular patterns (PAMP), used by the original virus for targeting DC, and are particularly efficient and versatile gene delivery vectors. Efforts in the field of synthetic vaccine carriers are focussing on decorating the particle surface with ligands for DC receptors such as heparan sulphate glycosaminoglycan structures, integrins, Siglecs, galectins, C-type lectins and toll-like receptors. The emphasis of this review will be placed on targeting the porcine immune system, but reference will be made to advances with murine and human vaccine delivery systems where information on DC targeting is available.

Vaccination against foot-and-mouth disease virus: strategies and effectiveness

Although present conventional foot-and-mouth disease (FMD) vaccines can prevent clinical disease, protection is short lived ( approximately 6 months), often requiring frequent revaccination for prophylactic control, and vaccination does not induce rapid protection against challenge or prevent the development of the carrier state. Furthermore, it is clear that the clinical protection depends upon the length of immunization and the duration of exposure/challenge methods. This review summarizes the present and future strategies for FMD control in endemic and FMD-free countries, the effectiveness of FMD vaccines in cattle, sheep and pigs, new methods for selecting vaccine strains, suggestions for alternative methods of vaccine testing, suggestions for the development of new-generation efficacious vaccines and their companion tests to differentiate infection in vaccinated animals.