Protection of pigs against classical swine fever with DNA-delivered gp55

Classical swine fever vaccines-State-of-the-art

Due to its impact on animal health and pig industry, classical swine fever (CSF) is still one of the most important viral diseases of pigs. To control the disease, safe and highly efficacious live attenuated vaccines exist for decades. These vaccines have usually outstanding efficacy and safety but lack differentiability of infected from vaccinated animals (DIVA or marker strategy). In contrast, the first generation of E2 subunit marker vaccines shows constraints in efficacy, application, and production. To overcome these limitations, new generations of marker vaccines are developed. A wide range of approaches have been tried including recombinant vaccines, recombinant inactivated vaccines or subunit vaccines, vector vaccines, and DNA/RNA vaccines. During the last years, especially attenuated deletion vaccines or chimeric constructs have shown potential. At present, especially two new constructs have been intensively tested, the adenovirus-delivered, Semliki Forest virus replicon-vectored marker vaccine candidate "rAdV-SFV-E2" and the pestivirus chimera "CP7_E2alf". The later was recently licensed by the European Medicines Agency. Under field conditions, all marker vaccines have to be accompanied by a potent test system. Particularly this point shows still weaknesses and it is important to embed vaccination in a well-established vaccination strategy and a suitable diagnostic workflow. In summary, conventional vaccines are a standard in terms of efficacy. However, only vaccines with DIVA will allow improved eradication strategies e.g. also under emergency vaccination conditions in free regions. To answer this demand, new generations of marker vaccines have been developed and add now to the tool box of CSF control.

Co-expression of the C-terminal domain of Yersinia enterocolitica invasin enhances the efficacy of classical swine-fever-vectored vaccine based on human adenovirus

The use of adenovirus vector-based vaccines is a promising approach for generating antigen-specific immune responses. Improving vaccine potency is necessary in other approaches to address their inadequate protection for the majority of infectious diseases. This study is the first to reconstruct a recombinant replication-defective human adenovirus co-expressing E2 and invasin C-terminal (InvC) glycoproteins (rAd-E2-InvC). rAd-E2-InvC with 2 x 10(6) TCID50 was intramuscularly administered two times to CSFV-free pigs at 14 day intervals. No adverse clinical reactions were observed in any of the pigs after the vaccination. The CSFV E2-specific antibody titer was significantly higher in the rAd-E2-InvC group than that in the rAdV-E2 group as measured by NPLA and blocking ELISA. Pigs immunized with rAd-E2-InvC were completely protected against lethal challenge. Neither CSFV RNA nor pathological changes were detected in the tissues after CSFV challenge. These results demonstrate that rAd-E2-InvC could be an alternative to the existing CSF vaccine. Moreover, InvC that acts as an adjuvant could enhance the immunogenicity of rAdV-E2 and induce high CSFV E2-specific antibody titer and protection level.

Classical swine fever in pigs: recent developments and future perspectives

Classical swine fever (CSF) is one of the most devastating epizootic diseases of pigs, causing high morbidity and mortality worldwide. The diversity of clinical signs and similarity in disease manifestations to other diseases make CSF difficult to diagnose with certainty. The disease is further complicated by the presence of a number of different strains belonging to three phylogenetic groups. Advanced diagnostic techniques allow detection of antigens or antibodies in clinical samples, leading to implementation of proper and effective control programs. Polymerase chain reaction (PCR)-based methods, including portable real-time PCR, provide diagnosis in a few hours with precision and accuracy, even at the point of care. The disease is controlled by following a stamping out policy in countries where vaccination is not practiced, whereas immunization with live attenuated vaccines containing the 'C' strain is effectively used to control the disease in endemic countries. To overcome the problem of differentiation of infected from vaccinated animals, different types of marker vaccines, with variable degrees of efficacy, along with companion diagnostic assays have been developed and may be useful in controlling and even eradicating the disease in the foreseeable future. The present review aims to provide an overview and status of CSF as a whole with special reference to swine husbandry in India.

Co-expression of Erns and E2 genes of classical swine fever virus by replication-defective recombinant adenovirus completely protects pigs against virulent challenge with classical swine fever virus

The objective of this study was to construct a recombinant adenovirus for future CSFV vaccines used in the pig industry for the reduction of losses involved in CSF outbreaks. The Erns and E2 genes of classical swine fever virus (CSFV), which encode the two main protective glycoproteins from the "Shimen" strain of CSFV, were combined and inserted into the replication-defective human adenovirus type-5 and named the rAd-Erns-E2. Nine pigs were randomly assigned to three treatment groups (three pigs in each group) including the rAd-Erns-E2, hAd-CMV control and DMEM control. Intramuscular vaccination with 2×10(6) TCID(50) of the rAd-Erns-E2 was administered two times with an interval of 21 days. At 42 days post inoculation, pigs in all groups were challenged with a lethal dose of 1×10(3) TCID(50) CSFV "Shimen" strain. Observation of clinical signs was made and the existence of CSFV RNA was detected. Animals in the hAd-CMV and DMEM groups showed severe clinical CSF symptoms and were euthanized from 7 to 10 days after the challenge. However, no adverse clinical CSF signs were observed in vaccinated pigs after the administration of rAd-Erns-E2 and even after CSFV challenge. Neither CSFV RNA nor pathological changes were detected in the tissues of interest of the above vaccinated pigs. These results implied that the recombination adenovirus carrying the Erns-E2 genes could be used to prevent swine from classical swine fever.

Current strategies for subunit and genetic viral veterinary vaccine development

Developing vaccines for livestock provides researchers with the opportunity to perform efficacy testing in the natural hosts. This enables the evaluation of different strategies, including definition of effective antigens or antigen combinations, and improvement in delivery systems for target antigens so that protective immune responses can be modulated or potentiated. An impressive amount of knowledge has been generated in recent years on vaccine strategies and consequently a wide variety of antigen delivery systems is now available for vaccine research. This paper reviews several antigen production and delivery strategies other than those based on the use of live viral vectors. Genetic and protein subunit vaccines as well as alternative production systems are considered in this review.

The Toll-like receptor adaptor molecule TRIF enhances DNA vaccination against classical swine fever

To evaluate the effects of the Toll/interleukin-1 receptor domain-containing adaptor-inducing interferon-beta (TRIF) on immune responses induced by DNA vaccines, mice were immunized with the eukaryotic expression plasmid pcDNA/E2 encoding classical swine fever virus (CSFV) E2 alone or in combination with the TRIF genetic adjuvant. Immune responses were examined in immunized mice. Our data demonstrates that co-delivery of the DNA vaccine pcDNA/E2 with the TRIF adjuvant augmented specific humoral and cellular immune responses in a mouse model. Vaccination of pigs confirmed that the pcDNA/E2 in combination with TRIF conferred total protection against lethal challenge with highly virulent CSFV. We conclude that TRIF enhances the effects of the DNA vaccine against CSFV infection and could be used as a potential genetic adjuvant for DNA vaccines in large animal species.

Strategies for differentiating infection in vaccinated animals (DIVA) for foot-and-mouth disease, classical swine fever and avian influenza

The prophylactic use of vaccines against exotic viral infections in production animals is undertaken exclusively in regions where the disease concerned is endemic. In such areas, the infection pressure is very high and so, to assure optimal protection, the most efficient vaccines are used. However, in areas considered to be free from these diseases and in which there is the possibility of only limited outbreaks, the use of Differentiation of Infected from Vaccinated Animals (DIVA) or marker vaccines allows for vaccination while still retaining the possibility of serological surveillance for the presence of infection. This literature review describes the current knowledge on the use of DIVA diagnostic strategies for three important transboundary animal diseases: foot-and-mouth disease in cloven-hoofed animals, classical swine fever in pigs and avian influenza in poultry.

Interferon-gamma induction correlates with protection by DNA vaccine expressing E2 glycoprotein against classical swine fever virus infection in domestic pigs

Classical swine fever (CSF) is a highly contagious viral infection affecting domestic and wild pigs. For classical swine fever virus (CSFV), immunization with plasmids expressing different versions of glycoprotein E2 has proven an effective way to induce protection. Previously, we have also shown that immunization with DNA vaccine expressing glycoprotein E2 (DNA-E2) induced specific T helper cell responses in the absence of neutralizing antibodies. However, the role of T cell responses in protection against CSFV is largely unknown. Here we have extended these studies to deeply characterize the role of T cell responses by a DNA-E2 and their correlation with protection against CSFV infection. Thus, pigs vaccinated with the DNA vaccine induced a strong cellular immune response, characterized by the specific induction IFN-gamma expressing T cells after vaccination without any detectable levels of CSFV neutralizing antibodies. Constant levels of CSFV-specific IFN-gamma producing cells observed from the beginning of the infection until 7 days after challenge in vaccinated animals might contribute to early control of CSFV replication, at least until neutralizing antibodies are developed. Severe clinical signs of the disease, including high titers of viremia, pyrexia and virus spread to different organs, were recorded in the non-vaccinated challenged animals, in comparison to the vaccinated animals where only one animal showed mild clinical signs and a short peak of viremia. Lack of complete protection in this animal correlated with a delay on the induction of neutralizing antibodies, detectable only from day 11 post-CSFV challenge. Conversely, the rest of the pigs within the group developed neutralizing antibodies as early as at day two post-challenge, correlating with sterile protection. Finally, an inverse correlation seemed to exist between early induction of IFN-alpha and the protection observed, while IL-10 seemed to be differentially regulated in vaccinated and non-vaccinated animals. Our results support the relevance of the induction of a strong T cellular response to confer a solid protection upon DNA vaccination against CSFV. Further experiments are needed to be done in order to clarify the key cytokines playing a role in CSFV-protection and to obtain emergency vaccines capable to confer robust and fast protection.

Baculovirus surface display of E(rns) envelope glycoprotein of classical swine fever virus

Classical swine fever virus (CSFV) causes significant losses in the pig industry in many countries. E(rns) is an envelope glycoprotein of CSFV which is known to induce virus-neutralizing antibodies and protective immunity in the natural host. In this study, one recombinant baculoviruses BacSC-E(rns) expressing histidine-tagged E(rns) with the transmembrane domain (TM) and cytoplasmic domain (CTD) derived from baculovirus envelope protein gp64 was constructed and its immunizing efficacy was evaluated in a mouse model. After infection, E(rns) was expressed and anchored on the plasma membrane of Sf-9 cells, as demonstrated by Western-blot and confocal microscopy. Immunogold electron microscopy demonstrated that the E(rns) glycoprotein was successfully displayed on the baculoviral envelope. Vaccine tests in animals showed that BacSC-E(rns) elicited significantly higher E(rns) antibody titers in the immunized mouse models than the control group. This demonstrates that the BacSC-E(rns) vaccine can be used potentially against CSFV infections. This is the first report demonstrating the potential of E(rns)-pseudotyped baculovirus as a CSFV vaccine.

Sustained biological effects of porcine interleukin 5 delivered to pigs as recombinant protein or via a DNA vector

The ability of cytokines to act as natural immunotherapeutics to enhance the health and the disease resistance of animals is of particular interest to the intensive livestock industries. Antibiotics have been used for such purposes over a long period of time, however, there is growing concern that this practice will enhance the development of antibiotic resistance in a range of bacterial pathogens. In several species, interleukin 5 (IL-5) is known to enhance B cell activity and to increase the numbers of eosinophils in blood and tissues. In this report, IL-5 was delivered to pigs, either as a recombinant protein or via a DNA delivery vector and was shown to elevate eosinophils in blood over a sustained period. Interleukin 3, a potent haemopoietic factor, did not synergize with IL-5 when both cytokines were given together, but did prime the pigs for a stronger response to IL-5. These results demonstrate that IL-5 can readily be delivered to commercial pigs to elicit a significant biological effect.

Recent advances in the development of recombinant vaccines against classical swine fever virus: cellular responses also play a role in protection

Classical swine fever virus (CSFV) is the causative agent of one of the most devastating porcine haemorrhagic viral diseases, classical swine fever (CSF). CSFV mainly infects endothelial cells and macrophages and at the same time promotes bystander apoptosis of the surrounding T cells, causing strong immune suppression and high mortality rates. Most animals experience acute infection, during which they either die or survive by producing neutralising antibodies to the virus. However, in a few cases, the impaired immune system cannot control viral progression, leading to chronic infection. Efficient live attenuated vaccines against CSFV exist and are routinely used only in endemic countries. The ability of these vaccines to replicate in the host, even at very low rates, makes it extremely difficult to distinguish vaccinated from infected animals, favouring a restricted policy regarding vaccination against CSFV in non-endemic countries. There is a clear need for efficient and safer marker vaccines to assist in the control of future CSF outbreaks. In this review article, some of the most recent advances in the field of recombinant vaccines against CSFV are presented and the nature of the protective immune responses they induce is discussed.

Protection of pigs from lethal challenge by a DNA vaccine based on an alphavirus replicon expressing the E2 glycoprotein of classical swine fever virus

In a previous study, it has been shown that a Semliki Forest virus (SFV) replicon vectored DNA vaccine (pSFV1CS-E2) expressing the E2 glycoprotein of classical swine fever virus (CSFV) conferred full protection for pigs immunized three times with 600 microg of the vaccine. This study was designed to evaluate further the efficacy of the vaccine with lower dosage and fewer inoculations. Pigs were immunized twice with 100 microg of pSFV1CS-E2 (n=5) or control plasmid pSFV1CS (n=3), respectively, and challenged with virulent Shimen strain 6 weeks following the booster immunization. Pigs immunized with pSFV1CS-E2 developed high titers of specific neutralizing antibodies against CSFV after the booster, and the antibody titers increased rapidly upon challenge. The immunized animals showed no clinical symptoms except short-term fever and low-level viremia, whereas, the control pigs immunized with the control plasmid produced no detectable antibody prior to challenge, and showed obvious clinical signs following challenge, and two pigs died of illness. All control animals developed extended viremia as detected by nested RT-PCR and real-time RT-PCR. Severe pathologic lesions typical of CSFV infection were observed at necropsy. It is concluded that the alphavirus replicon-vectored DNA-based vaccine can be a potential marker vaccine against CSFV.

Efficient priming against classical swine fever with a safe glycoprotein E2 expressing Orf virus recombinant (ORFV VrV-E2)

An increasing demand in livestock animal husbandry for intervention or emergency vaccination strategies requires a rapid onset of protection linked to prevention of infectious agent spread. Using the new recombinant parapoxvirus (PPV) Orf virus (ORFV) as a vaccine expressing the CSFV E2 glycoprotein we demonstrate that a single intra-muscular application confers solid protection. In the prime only concept, multi-site application of the vector vaccine turned out to be superior to single-site application as no pyrexia occurred after virulent CSFV challenge and CSFV neutralizing serum antibodies regularly were detectable before challenge. Vector virus vaccinated swine were able to cope with the lymphocyte and in particular B-cell depression in peripheral blood after challenge showing no clinical signs and no viremia. Early after challenge CSFV-specific IFN gamma production (IFN-gamma) and high neutralizing serum antibody titers clearly differentiated naïve from vaccinated and protected animals. After CSFV challenge neutralizing serum antibodies titers in vector vaccinated swine were significantly higher than those in sera from live attenuated vaccine primed animals. Horizontal challenge virus transmission was prevented under strict sentinel isolation before mingling but not in next-door stables separated by a wooden barrier at the day of challenge. The presence of CSFV-specific pre-challenge serum antibodies although in low titers is a good prognostic parameter for solid protection after ORFV vector vaccination even when a significant CSFV-specific IFN-gamma production was not detectable before challenge. A heterologous prime-boost regimen as a combination of prime with baculovirus-expressed glycoprotein E2 followed by boost with the parapoxvirus vector turned out to be a better immune stimulant than a homologous prime/boost with the modified live CSFV vaccine. A similar beneficial effect became evident when the challenge infection mimicked the booster vaccination after a single PPV vector prime.

Novel marker vaccines against classical swine fever

Classical swine fever (CSF) is one of the most devastating epizootic diseases of pigs worldwide. For eradication and control purposes, CSF vaccination is an important tool, and efficacious and safe attenuated vaccines have been available for many decades (for example, the C-strain vaccines). In addition to administering them parenterally, live attenuated vaccines are also administered orally for the control and eradication of CSF in wild boar populations. However, antibodies against live attenuated vaccines do not allow to differentiate infected from vaccinated animals (DIVA principle) and the mechanism responsible for attenuation is not known. Only a few years ago the first DIVA vaccines based on baculovirus-expressed E2 glycoprotein have been put on the market [Hulst MM, Westra DF, Wensvoort G, Moormann RJ. Glycoprotein E1 of hog cholera virus expressed in insect cells protects swine from hog cholera. J Virol 1993;67(9):5435-42]. However, these subunit E2 marker vaccines are less efficient and more than one parenteral application is necessary. Furthermore, oral vaccination is not possible. Taking these disadvantages into account, the development of novel CSF vaccines has been focussed on five different strategies, mainly based on genetically engineered constructs: (1) immunogenic CSFV peptides, (2) DNA vaccines, (3) viral vectors expressing CSFV proteins, (4) chimeric pestiviruses, and (5) trans-complemented deleted CSFV genomes (replicons).

Marker vaccine strategies and candidate CSFV marker vaccines

Classical swine fever (CSF) is an economically important highly contagious disease of swine worldwide. Classical swine fever virus (CSFV) is its etiological agent, and the only natural hosts are domestic pigs and wild boars. Although field CSFV strains vary in the virulence, they all result in serious losses in pig industry. Highly virulent field strains generally cause acute disease and high mortality; moderately virulent field strains raise subacute or chronic infections; postnatal infection by low virulent field strains produces subclinical infection and mortality in the new-born piglets. CSFV can cross the placental barrier, and this transplacental transmission usually results in mortality of fetuses and birth of congenitally infected pigs with a late-onset disease and death. Two main strategies to control CSF epidemic are systematic prophylactic vaccination with live attenuated vaccines (such as C-strain) and non-vaccination stamping-out policy. But neither of them is satisfying enough. Marker vaccine and companion serological diagnostic test is thought to be a promising strategy for future control and eradication of CSF. During the past 15 years, various candidate marker vaccines were constructed and evaluated in the animal experiments, including recombinant chimeric vaccines, recombinant deletion vaccines, DNA vaccines, subunit vaccines and peptide vaccines. Among them, two subunit vaccines entered the large scale marker vaccine trial of EU in 1999. Although they failed to fulfil all the demands of the Scientific Veterinary Committee, they successfully induced solid immunity against CSFV in the vaccinated pigs. It can be expected that new potent marker vaccines might be commercially available and used in systematic prophylactic vaccination campaign or emergency vaccination in the next 15 years. Here, we summarized current strategies and candidate CSFV marker vaccines. These strategies and methods are also helpful for the development of new-generation vaccines against other diseases.

Recombination and expression of classical swine fever virus (CSFV) structural protein E2 gene in Chlamydomonas reinhardtii chroloplasts

The expression of classical swine fever virus (CSFV) structural protein E2 in different vectors, which has been shown to carry critical epitopes, has been established. Here, we reported a Chlamydomonas reinhardtii chloroplast expression vector, P64E2, containing classical swine fever virus structural protein E2 gene, which was constructed and transferred to C. reinhardtii by biolistic bombardment method. The transformants were identified by PCR, Southern blotting, Western blotting after selecting on resistant media. ELISA quantification assay showed that the expressed E2 protein accumulated up to 1.5-2% of the total soluble protein. The results of the study on the immunological activity indicated that the protein E2 expressed in C. reinhardtii chloroplasts could elicit animal bodies to produce antibodies against protein E2.

A Semliki Forest virus replicon vectored DNA vaccine expressing the E2 glycoprotein of classical swine fever virus protects pigs from lethal challenge

Classical swine fever virus (CSFV) causes significant losses in pig industry in many countries in Asia and Europe. The E2 glycoprotein of CSFV is the main target for neutralizing antibodies. Recently, the replicon of alphaviruses, such as Semliki Forest virus (SFV), has been developed as replicative expression vectors for gene delivery. In this study, we constructed a plasmid DNA based on SFV replicon encoding the E2 glycoprotein of CSFV and evaluated its efficacy in rabbits and pigs. The results showed that the animals immunized with the DNA vaccine developed CSFV-specific neutralizing antibodies and were protected from virulent or lethal challenge. This demonstrates that the SFV replicon-derived DNA vaccine can be a potential marker vaccine against CSFV infections.

Vaccinology of classical swine fever: from lab to field

There are two types of classical swine fever vaccines available: the classical live and the recently developed E2 subunit vaccines. The live Chinese strain vaccine is the most widely used. After a single vaccination, it confers solid immunity within a few days that appears to persist lifelong. The E2 subunit vaccine induces immunity from approximately 10-14 days after a single vaccination. The immunity may persist for more than a year, but is then not complete. The Chinese strain vaccine may establish a strong herd immunity 1-2 weeks earlier than the E2 vaccine. The ability of the Chinese vaccine strain to prevent congenital infection has not been reported, but the E2 subunit vaccine does not induce complete protection against congenital infection. Immunological mechanisms that underlie the protective immunity are still to be elucidated. Both types of vaccine are considered to be safe. A great advantage of the E2 subunit vaccine is that it allows differentiation of infected pigs from vaccinated pigs and is referred to as a DIVA vaccine. However, the companion diagnostic E(rns) ELISA to actually make that differentiation should be improved. Many approaches to develop novel vaccines have been described, but none of these is likely to result in a new DIVA vaccine reaching the market in the next 5-10 years. Countries where classical swine fever is endemic can best control the infection by systematic vaccination campaigns, accompanied by the normal diagnostic procedures and control measures. Oral vaccination of wild boar may contribute to lowering the incidence of classical swine fever, and consequently diminishing the threat of virus introduction into domestic pigs. Free countries should not vaccinate and should be highly alert to rapidly diagnose any new outbreak. Once a new introduction of classical swine fever virus in dense pig areas has been confirmed, an emergency vaccination programme should be immediately instituted, for maximum benefit. The question is whether the time is ripe to seriously consider global eradication of classical swine fever virus.

Candidate peptide vaccine induced protection against classical swine fever virus

Former investigations demonstrated that the envelope glycoprotein E2 could protect pigs from classical swine fever virus (CSFV). Based on these findings, we prepared synthetic peptide vaccine using E2 N-terminal antigenic units B/C and hoped to induce protective activity against lethal challenge of virulent CSFV strain Shimen. Five overlapped peptides sequence-covering amino acids 693-777 on E2 of Shimen were synthesized and then conjugated with bovine serum albumin (BSA), respectively. In the vaccination course, the candidate peptide vaccines in combination (multi-peptide vaccine (MPV)) were applied for immunization of pigs (n=10) and induced strong antibody response against CSFV. It is subsequently demonstrated that this peptide vaccine could provide immunized pigs complete protection against lethal CSFV challenge as C-strain does, while all non-immunized pigs in negative control group manifested obvious typical symptoms and died during the second and third weeks after viral challenge. In order to confirm the neutralizing activity of the polyclonal antibodies induced by MPV, neutralization assay were carried out on rabbits. The live C-strain alone could ordinarily induce typical fever on rabbits. The typical fever of rabbits induced by the live C-strain could be inhibited by pre-incubation with the anti-sera (dilution 1:4 and 1:16) induced by MPV, but not inhibited by pre-incubation with the same anti-sera from which the antibodies against five peptides were removed by peptide-specific affinity chromatography, which indicates that these peptide-specific antibodies in the anti-sera induced by MPV provided protective activity against CSFV. Our finding provides a new way to develop marker vaccine against CSFV.

Identification of T-cell epitopes in the structural and non-structural proteins of classical swine fever virus

To identify new T-cell epitopes of classical swine fever virus (CSFV), 573 overlapping, synthetic pentadecapeptides spanning 82% of the CSFV (strain Glentorf) genome sequence were synthesized and screened. In proliferation assays, 26 peptides distributed throughout the CSFV viral protein sequences were able to induce specific T-cell responses in PBMCs from a CSFV-Glentorf-infected d/d haplotype pig. Of these 26 peptides, 18 were also recognized by PBMCs from a CSFV-Alfort/187-infected d/d haplotype pig. In further experiments, it could be shown that peptide 290 (KHKVRNEVMVHWFDD), which corresponds to amino acid residues 1446-1460 of the CSFV non-structural protein NS2-3 could induce interferon-gamma secretion after secondary in vitro restimulation. The major histocompatibility complex (MHC) restriction for stimulation of T-cells by this pentadecapeptide was identified as being mainly MHC class II and partially MHC class I. In cytolytic assays, CSFV-specific cytotoxic T-lymphocytes (CTLs) were able to lyse peptide 290-loaded target cells. These findings indicate the existence of a CSFV-specific helper T-cell epitope and a CTL epitope in this peptide.

A prime-boost vaccination strategy using naked DNA followed by recombinant porcine adenovirus protects pigs from classical swine fever

Weaned pigs (6-week-old) and 7-day-old pre-weaned piglets were vaccinated with naked plasmid DNA expressing the gp55/E2 gene from classical swine fever virus (CSFV). Both groups of pigs were then given a booster dose of recombinant porcine adenovirus expressing the gp55 gene (rPAV-gp55). Following challenge with CSFV, 100% of weaned pigs and 75% pre-weaned piglets were protected from disease. Weaned pigs given a single dose of rPAV-gp55 were also protected, but showed a slight increase in temperature immediately post-challenge. However, weaned animals given a DNA prime before rPAV-gp55 showed no fluctuation in body temperature following challenge and no pathology in spleen or lymph nodes upon post-mortem. In addition, no CSFV could be re-isolated from the rPAV vaccinated group and from only one pig in the prime-boost group following challenge, suggesting that both vaccination regimes have the potential to reduce or prevent virus shedding following experimental challenge.

Laboratory diagnosis, epizootiology, and efficacy of marker vaccines in classical swine fever: a review

Detection of classical swine fever virus (CSFV) can be achieved by a range of assays of which the most commonly used are: immunohistochemical and virus culture techniques. New developments have enabled the detection of viral proteins by enzyme-linked immunosorbent assays (ELISAs) and the detection of the viral genome by RT- PCR. So far, laboratory findings show that the latter assays may supplement or replace the conventional techniques in the near future. The detection of serum antibody against structural and non-structural proteins of CSFV has been improved by developments in recombinant DNA techniques and has lead to a range of ELISAs. Although the characteristics of these ELISAs are excellent, positive results still need to be confirmed in the virus neutralization test. The available amount of sequence data enables diagnosticians to type strains of CSFV as different by comparing several parts of the genome. In some cases, this can provide conclusive evidence if a primary or secondary outbreak has been detected. Increased efforts focused on the retrieval of relevant data on the introduction of CSFV in a pig holding and the spread of CSFV in- and between pig holding(s) has generated more insight into the epizootiology of the disease. A successful control and eradication programme for classical swine fever (CSF) can consist of zoosanitary measures and/or vaccination. The latter can compromise the export of live pigs and pig products considerably unless marker vaccines have been used. Several studies were performed to determine the efficacy of an E2 subunit vaccine and live recombinant vaccine candidates. Firstly, we determined the 95% protective dose of an E2 subunit vaccine at 32 microg E2 per dosage after a single application. Further studies with a single administration of the subunit vaccine showed that: the vaccine was stable for a prolonged period after production, was able to reduce horizontal and vertical transmission of CSFV among vaccinated pigs, and provided protection for at least 6 months. An E(rns) antibody discriminatory assay was developed for use in combination with the subunit vaccine. Evaluation of the E(rns) ELISA showed that the sensitivity of the assay was lower than but that the specificity was equal to that of existing antibody assays. Two live recombinant marker vaccines were evaluated for the induction of clinical protection and reduction of transmission of CSFV shortly after vaccination. Results showed that these vaccines provided good clinical protection 1 week after a single vaccination. Research has shown that marker vaccines can be used in the future to support the control and eradication of CSFV.