Classical swine fever (CSF) marker vaccine. Trial I. Challenge studies in weaner pigs

Intranasal Inoculation with Classical Swine Fever Virus Provided a More Consistent Experimental Disease Model Compared to Oral Inoculation

The severity of disease resulting from classical swine fever virus (CSFV) infection is determined by several factors, including virus strain and host factors. The different outcomes of experimental studies in pigs with the same strain of CSFV emphasize the need to elucidate the influence of individual factors within experimental protocols. In this study, we investigated the outcome of disease after oral and intranasal inoculation with a moderately virulent CSFV strain in young pigs. To compare the two routes of inoculation, various infection parameters were examined during a period of two weeks. While all intranasally inoculated pigs (n = 5) were directly infected, this was only the case for two out of five pigs after oral inoculation. In addition, the intranasally inoculated pigs developed a more pronounced clinical disease and pathological lesions, as well as markedly more change in hematological and immunological parameters than the orally inoculated pigs. The wide variation among the orally inoculated pigs implied that statistical evaluation was markedly impaired, leaving this route of application less suitable for comparative studies on classical swine fever. Furthermore, our study provides additional details about the immunomodulatory effects of CSFV on the kinetics of CRP, TNF-α, and leukocyte sub-populations in pigs after infection with the CSFV strain Paderborn.

Bridging the Gap: Can COVID-19 Research Help Combat African Swine Fever?

African swine fever (ASF) is a highly contagious and economically devastating disease affecting domestic pigs and wild boar, caused by African swine fever virus (ASFV). Despite being harmless to humans, ASF poses significant challenges to the swine industry, due to sudden losses and trade restrictions. The ongoing COVID-19 pandemic has spurred an unparalleled global research effort, yielding remarkable advancements across scientific disciplines. In this review, we explore the potential technological spillover from COVID-19 research into ASF. Specifically, we assess the applicability of the diagnostic tools, vaccine development strategies, and biosecurity measures developed for COVID-19 for combating ASF. Additionally, we discuss the lessons learned from the pandemic in terms of surveillance systems and their implications for managing ASF. By bridging the gap between COVID-19 and ASF research, we highlight the potential for interdisciplinary collaboration and technological spillovers in the battle against ASF.

Application of Baculovirus Expression Vector System (BEVS) in Vaccine Development

Vaccination is one of the most effective strategies to control epidemics. With the deepening of people's awareness of vaccination, there is a high demand for vaccination. Hence, a flexible, rapid, and cost-effective vaccine platform is urgently needed. The baculovirus expression vector system (BEVS) has emerged as a promising technology for vaccine production due to its high safety, rapid production, flexible product design, and scalability. In this review, we introduced the development history of BEVS and the procedures for preparing recombinant protein vaccines using the BEVS platform and summarized the features and limitations of this platform. Furthermore, we highlighted the progress of the BEVS platform-related research, especially in the field of vaccine. Finally, we provided a new prospect for BEVS in future vaccine manufacturing, which may pave the way for future BEVS-derived vaccine development.

Neutralizing antibodies as a correlate of protection against classical swine fever in Porvac® vaccinated pigs

Porvac is a classical swine fever (CSF) subunit vaccine. It is safe and induces a robust neutralizing antibody response, sterilizing immunity, and early protection, and it prevents vertical transmission in pregnant sows. The methodology to approve Porvac batches is a challenging experiment in pigs with a virulent CSF virus strain. However, there is an ethical reason to reduce, at minimum, the use of animals in these lethal experiments. The knowledge indicates that neutralizing antibody titers in the blood could be a good correlate of protection. The results of 22 challenge experiments involving 116 Porvac vaccinated and 38 unvaccinated animals were analyzed. All vaccinated animals remained free from CSF clinical signs and pathological lesions and were negative for viral isolation after the challenge. In contrast, all unvaccinated pigs developed clinical and pathological signs of the disease and had to be euthanized eight days post-challenge. All vaccinated pigs exhibited high neutralizing antibody titers, with a geometric mean value of 1: 5153. The lower titer registered was 1: 800. A complete correspondence between neutralizing antibody titers and protection was demonstrated. These results support substituting the viral challenge test for the neutralizing peroxidase-linked assay in the release of Porvac® batches. Keywords. Classical swine fever; virus; subunit vaccine; viral challenge; neutralizing antibodies

Cross-reactivities and cross-neutralization of different envelope glycoproteins E2 antibodies against different genotypes of classical swine fever virus

Classical swine fever (CSF) is a highly contagious swine disease caused by the classical swine fever virus (CSFV), wreaking havoc on global swine production. The virus is divided into three genotypes, each comprising 4-7 sub-genotypes. The major envelope glycoprotein E2 of CSFV plays an essential role in cell attachment, eliciting immune responses, and vaccine development. In this study, to study the cross-reaction and cross-neutralizing activities of antibodies against different genotypes (G) of E2 glycoproteins, ectodomains of G1.1, G2.1, G2.1d, and G3.4 CSFV E2 glycoproteins from a mammalian cell expression system were generated. The cross-reactivities of a panel of immunofluorescence assay-characterized serum derived from pigs with/without a commercial live attenuated G1.1 vaccination against different genotypes of E2 glycoproteins were detected by ELISA. Our result showed that serum against the LPCV cross-reacted with all genotypes of E2 glycoproteins. To evaluate cross-neutralizing activities, hyperimmune serum from different CSFV E2 glycoprotein-immunized mice was also generated. The result showed that mice anti-E2 hyperimmune serum exhibited better neutralizing abilities against homologous CSFV than heterogeneous viruses. In conclusion, the results provide information on the cross-reactivity of antibodies against different genogroups of CSFV E2 glycoproteins and suggest the importance of developing multi-covalent subunit vaccines for the complete protection of CSF.

Complete genome sequences of classical swine fever virus: Phylogenetic and evolutionary analyses

The classical swine fever virus (CSFV) outbreaks cause colossal losses of pigs and drastic economic impacts. The current phylogenetic CSFV groups were determined mainly based on the partial genome. Herein, 203 complete genomic sequences of CSFVs collected worldwide between 1998 and 2018 available on the GenBank database were retrieved for re-genotyping and recombination analysis. The maximum likelihood phylogenetic tree determined two main groups, GI and GII, with multiple sub-genotypes. The “strain 39” (GenBank ID: AF407339), previously identified as belonging to sub-genotypes 1.1 or 2.2 based on the partial sequences, is found to be genetically distinct and independent, forming a new lineage depicted as GI-2.2b. Ten potential natural recombination events were identified, seven of which were collected in China and found involved in the genetic diversity of CSFVs. Importantly, the vaccine strains and highly virulent strains were all involved in the recombination events, which would induce extra challenges to vaccine development. These findings alarm that attenuated vaccines should be applied with discretion and recommend using subunit vaccines in parallel with other preventive strategies for better management of CSFVs.

Safety and immunogenicity in piglets of two immunization schedules initiated at two or three weeks of age with PorvacÒ, a classical swine fever subunit marker vaccine

Classical swine fever is a highly contagious viral disease with a significant impact on food production worldwide. It currently represents one of the main limitations for the development of the pig industry in Cuba. PorvacÒ is a subunit marker vaccine that confers a very rapid onset of protection. Since there are different production systems in pig breeding, readjustments in the vaccination program are often required. This study compares the safety and efficacy in piglets of two vaccination schedules with PorvacÒ (0-2 weeks and 0-3 weeks), initiated at two or three weeks of age. Clinical monitoring was conducted, and a neutralization peroxidase-linked assay was used to measure the neutralization titers. All immunization regimens were safe and well-tolerated, without local or systemic adverse reactions in the vaccinated animals. Geometric mean neutralizing antibody titers higher than 1/1500 were detected in all groups during the six months of the trial. One month after the second immunization, piglets primed at two weeks of age, and boostered three weeks later, developed significantly higher neutralization titers (1/15644) compared to those vaccinated at a similar age but with a two-week interval between doses (1/5760). However, no significant differences in the titers were found three and six months after vaccination among the four regimens. In summary, all the variants studied are effective, but it is recommended to start vaccination at two weeks old, with the second dose at either two or three weeks later, depending on the production system and the purpose of the farm.

Assessment of the control measures of the category A diseases of Animal Health Law: Classical Swine Fever

EFSA received a mandate from the European Commission to assess the effectiveness of some of the control measures against diseases included in the Category A list according to Regulation (EU) 2016/429 on transmissible animal diseases ('Animal Health Law'). This opinion belongs to a series of opinions where these control measures will be assessed, with this opinion covering the assessment of control measures for Classical swine fever (CSF). In this opinion, EFSA and the AHAW Panel of experts review the effectiveness of: (i) clinical and laboratory sampling procedures, (ii) monitoring period and (iii) the minimum radii of the protection and surveillance zones, and the minimum length of time the measures should be applied in these zones. The general methodology used for this series of opinions has been published elsewhere; nonetheless, details of the model used for answering these questions are presented in this opinion as well as the transmission kernels used for the assessment of the minimum radius of the protection and surveillance zones. Several scenarios for which these control measures had to be assessed were designed and agreed prior to the start of the assessment. Here, several recommendations are given on how to increase the effectiveness of some of the sampling procedures. Based on the average length of the period between virus introduction and the reporting of a CSF suspicion, the monitoring period was assessed as non-effective. In a similar way, it was recommended that the length of the measures in the protection and surveillance zones were increased from 15 to 25 days in the protection zone and from 30 to 40 days in the surveillance zone. Finally, the analysis of existing Kernels for CSF suggested that the radius of the protection and the surveillance zones comprise 99% of the infections from an affected establishment if transmission occurred. Recommendations provided for each of the scenarios assessed aim to support the European Commission in the drafting of further pieces of legislation, as well as for plausible ad hoc requests in relation to CSF.

A Critical Review about Different Vaccines against Classical Swine Fever Virus and Their Repercussions in Endemic Regions

Classical swine fever (CSF) is, without any doubt, one of the most devasting viral infectious diseases affecting the members of Suidae family, which causes a severe impact on the global economy. The reemergence of CSF virus (CSFV) in several countries in America, Asia, and sporadic outbreaks in Europe, sheds light about the serious concern that a potential global reemergence of this disease represents. The negative aspects related with the application of mass stamping out policies, including elevated costs and ethical issues, point out vaccination as the main control measure against future outbreaks. Hence, it is imperative for the scientific community to continue with the active investigations for more effective vaccines against CSFV. The current review pursues to gather all the available information about the vaccines in use or under developing stages against CSFV. From the perspective concerning the evolutionary viral process, this review also discusses the current problematic in CSF-endemic countries.

Plasticity of the HEK-293 cells, related to the culture media, as platform to produce a subunit vaccine against classical swine fever virus

Classical swine fever (CSF) is a contagious disease that causes a high mortality to domestic and wild pigs. Its causative agent is an enveloped Pestivirus named Classical Swine Fever Virus (CSFV). Due to the huge economic affectations produced by this disease to porcine industry, several vaccines have been developed using principally the CSFV E2 glycoprotein. Recently, a subunit vaccine based on this structural protein of the CSFV fused to the porcine CD154 molecule as immunomodulator named E2-CD154 was assayed by us. This chimeric protein was produced in the Human Embryonic Kidney (HEK-293) cell line. In this work, the growth and the expression profiles of HEK-293 E2-CD154 cells in four commercially available culture media were studied. The oligosaccharide structures in the N-glycosylation patterns of the E2-CD154 protein produced by this cell line in 10 L fermenters with two different culture media were also analyzed. In addition, the neutralizing antibody response generated in mice vaccinated with these antigens was assayed. Our results suggest that the culture media CDM4HEK293 and SFM4HEK293 which are recommended for HEK-293 growth are the best choice to growth the cell clone expressing the E2-CD154 protein. The glycosylation pattern and the neutralizing antibody response generated by the E2-CD154 protein were independent of the culture medium used which demonstrates the high reproducibility and consistency among protein batches produced by HEK-293 cells even in different culture conditions.

Plant-made E2 glycoprotein single-dose vaccine protects pigs against classical swine fever

Classical Swine Fever Virus (CSFV) causes classical swine fever, a highly contagious hemorrhagic fever affecting both feral and domesticated pigs. Outbreaks of CSF in Europe, Asia, Africa and South America had significant adverse impacts on animal health, food security and the pig industry. The disease is generally contained by prevention of exposure through import restrictions (e.g. banning import of live pigs and pork products), localized vaccination programmes and culling of infected or at-risk animals, often at very high cost. Current CSFV-modified live virus vaccines are protective, but do not allow differentiation of infected from vaccinated animals (DIVA), a critical aspect of disease surveillance programmes. Alternatively, first-generation subunit vaccines using the viral protein E2 allow for use of DIVA diagnostic tests, but are slow to induce a protective response, provide limited prevention of vertical transmission and may fail to block viral shedding. CSFV E2 subunit vaccines from a baculovirus/insect cell system have been developed for several vaccination campaigns in Europe and Asia. However, this expression system is considered expensive for a veterinary vaccine and is not ideal for wide-spread deployment. To address the issues of scalability, cost of production and immunogenicity, we have employed an Agrobacterium-mediated transient expression platform in Nicotiana benthamiana and formulated the purified antigen in novel oil-in-water emulsion adjuvants. We report the manufacturing of adjuvanted, plant-made CSFV E2 subunit vaccine. The vaccine provided complete protection in challenged pigs, even after single-dose vaccination, which was accompanied by strong virus neutralization antibody responses.

Development of Recombinant Protein-Based Vaccine Against Classical Swine Fever Virus in Pigs Using Transgenic Nicotiana benthamiana

Classical swine fever virus (CSFV) is highly contagious, and fatal to infected pigs. Vaccines against CSFV have been developed from attenuated or modified live viruses. These vaccines are effective for immunization of animals, but they are associated with problems such as the accidental spreading of viruses to animals in the field, and with barriers to trade following vaccination. Here, we report the generation of transgenic Nicotiana benthamiana plants for large-scale, cost-effective production of E2 fusion protein for use as a recombinant vaccine against CSFV in pigs. Transgenic N. benthamiana plants harboring an intergenic, single-copy insertion of a chimeric gene encoding E2 fusion protein had high levels of transgene expression. For large-scale production of E2 fusion protein from leaf tissues, we developed a protein-purification protocol consisting of cellulose-binding domain (CBD)-cellulose-based affinity purification and size-exclusion gel-filtration chromatography. E2 fusion proteins showed high immunogenicity in piglets and provided protection against CSFV challenge. The CBD in the E2 fusion protein was also highly immunogenic. These results suggest that plant-produced recombinant E2 fusion proteins can be developed into cost-effective vaccines against CSFV, with the CBD as a marker antigen to differentiate between vaccination and natural infection.

Recent Advances in Vaccine Technologies

This brief review discusses some recent advances in vaccine technologies with particular reference to their application within veterinary medicine. It highlights some of the key inactivated/killed approaches to vaccination, including natural split-product and subunit vaccines, recombinant subunit and protein vaccines, and peptide vaccines. It also covers live/attenuated vaccine strategies, including modified live marker/differentiating infected from vaccinated animals vaccines, live vector vaccines, and nucleic acid vaccines.

Epidemiology, diagnosis and control of classical swine fever: Recent developments and future challenges

Classical swine fever (CSF) represents a major health and trade problem for the pig industry. In endemic countries or those with a wild boar reservoir, CSF remains a priority for Veterinary Services. Surveillance as well as stamping out and/or vaccination are the principle tools of prevention and control, depending on the context. In the past decades, marker vaccines and accompanying diagnostic tests allowing the discrimination of infected from vaccinated animals have been developed. In the European Union, an E2 subunit and a chimeric live vaccine have been licensed and are available for the use in future disease outbreak scenarios. The implementation of commonly accepted and globally harmonized concepts could pave the way to replace the ethically questionable stamping out policy by a vaccination-to-live strategy and thereby avoid culling of a large number of healthy animals and save food resources. Although a number of vaccines and diagnostic tests are available worldwide, technological advancement in both domains is desirable. This work provides a summary of an analysis undertaken by the DISCONTOOLS group of experts on CSF. Details of the analysis can be downloaded from the web site at http://www.discontools.eu/.

Changing pattern of classical swine fever virus genogroup from classical 1.1 to emerging 2.2 in India

Classical swine fever (CSF) is one of the most important viral diseases of pigs with high economic impact. The causative agent, Classical swine fever virus (CSFV) is a member of genus Pestivirus in family Flaviviredae and is structurally and antigenically related to other members of the genus. The identification of virus strains and genotypes can conveniently be used to trace the origin and patterns of virus spread, which contribut substantially in control strategies. In the present study, we have partially sequenced and analysed the 5' untranslated region (UTR) and E2 regions of CSFV clinical samples (n = 24) from various parts of the country. Among the samples, the sequence alignment of 5'UTR and E2 regions revealed 96.7-100 and 94.7-100% identities at the nucleotide level, respectively. The samples under study showed the close resemblance to the other CSFV isolates reported in India. In phylogenetic analysis, all the field samples were clustered in subgroup 2.2. Thus the study presents a further phylogenetic evidence for the emergence of subgroup 2.2 CSFV replacing the predominant subgroup 1.1 viruses in India. As the information regarding the molecular epidemiology the CSFV in india is very little, generation of such epidemiological data is warranted to help in comprehensing the nationwide disease control program to sustain the growth of pig industry in India.

Controlling of CSFV in European wild boar using oral vaccination: a review

Classical swine fever (CSF) is among the most detrimental diseases for the swine industry worldwide. Infected wild boar populations can play a crucial role in CSF epidemiology and controlling wild reservoirs is of utmost importance for preventing domestic outbreaks. Oral mass vaccination (OMV) has been implemented to control CSF in wild boars and limit the spill over to domestic pigs. This retrospective overview of vaccination experiences illustrates the potential for that option. The C-strain live vaccine was confirmed to be highly efficacious and palatable baits were developed for oral delivery in free ranging wild boars. The first field trials were performed in Germany in the 1990’s and allowed deploying oral baits at a large scale. The delivery process was further improved during the 2000’s among different European countries. Optimal deployment has to be early regarding disease emergence and correctly designed regarding the landscape structure and the natural food sources that can compete with oral baits. OMV deployment is also highly dependent on a local veterinary support working closely with hunters, wildlife and forestry agencies. Vaccination has been the most efficient strategy for CSF control in free ranging wild boar when vaccination is wide spread and lasting for a sufficient period of time. Alternative disease control strategies such as intensified hunting or creating physical boundaries such as fences have been, in contrast, seldom satisfactory and reliable. However, monitoring outbreaks has been challenging during and after vaccination deployment since OMV results in a low probability to detect virus-positive animals and the live-vaccine currently available does not allow serological differentiation of infected from vaccinated animals. The development of a new marker vaccine and companion test is thus a promising option for better monitoring outbreaks during OMV deployment as well as help to better determine when to stop vaccination efforts. After rabies in red fox, the use of OMV against CSF in European wild boar can be considered as a second example of successful disease control in wildlife. The 30 years of disease control experience included in this review may provide options for improving future disease management within wild populations.

Structures and Functions of Pestivirus Glycoproteins: Not Simply Surface Matters

Pestiviruses, which include economically important animal pathogens such as bovine viral diarrhea virus and classical swine fever virus, possess three envelope glycoproteins, namely E^rns, E1, and E2. This article discusses the structures and functions of these glycoproteins and their effects on viral pathogenicity in cells in culture and in animal hosts. E2 is the most important structural protein as it interacts with cell surface receptors that determine cell tropism and induces neutralizing antibody and cytotoxic T-lymphocyte responses. All three glycoproteins are involved in virus attachment and entry into target cells. E1-E2 heterodimers are essential for viral entry and infectivity. E^rns is unique because it possesses intrinsic ribonuclease (RNase) activity that can inhibit the production of type I interferons and assist in the development of persistent infections. These glycoproteins are localized to the virion surface; however, variations in amino acids and antigenic structures, disulfide bond formation, glycosylation, and RNase activity can ultimately affect the virulence of pestiviruses in animals. Along with mutations that are driven by selection pressure, antigenic differences in glycoproteins influence the efficacy of vaccines and determine the appropriateness of the vaccines that are currently being used in the field.

The Molecular Biology of Pestiviruses

Pestiviruses are among the economically most important pathogens of livestock. The biology of these viruses is characterized by unique and interesting features that are both crucial for their success as pathogens and challenging from a scientific point of view. Elucidation of these features at the molecular level has made striking progress during recent years. The analyses revealed that major aspects of pestivirus biology show significant similarity to the biology of human hepatitis C virus (HCV). The detailed molecular analyses conducted for pestiviruses and HCV supported and complemented each other during the last three decades resulting in elucidation of the functions of viral proteins and RNA elements in replication and virus-host interaction. For pestiviruses, the analyses also helped to shed light on the molecular basis of persistent infection, a special strategy these viruses have evolved to be maintained within their host population. The results of these investigations are summarized in this chapter.

The challenges of classical swine fever control: modified live and E2 subunit vaccines

Classical swine fever (CSF) is an economically important, highly contagious disease of swine worldwide. CSF is caused by classical swine fever virus (CSFV), and domestic pigs and wild boars are its only natural hosts. The two main strategies used to control CSF epidemic are systematic prophylactic vaccination and a non-vaccination stamping-out policy. This review compares the protective efficacy of the routinely used modified live vaccine (MLV) and E2 subunit vaccines and summarizes the factors that influence the efficacy of the vaccines and the challenges that both vaccines face to CSF control. Although MLV provide earlier and more complete protection than E2 subunit vaccines, it has the drawback of not allowing differentiation between infected and vaccinated animals (DIVA). The marker vaccine of E2 protein with companion discriminatory test to detect antibodies against E(rns) allows DIVA and is a promising strategy for future control and eradication of CSF. Maternal derived antibody (MDA) is the critical factor in impairing the efficacy of both MLV and E2 subunit vaccines, so the well-designed vaccination programs of sows and piglets should be considered together. Because of the antigen variation among various genotypes of CSFV, antibodies raised by either MLV or subunit vaccine neutralize genotypically homologous strains better than heterologous ones. However, although this is not a major concern for MLV as the induced immune responses can protect pigs against the challenge of various genotypes of CSFVs, it is critical for E2 subunit vaccines. It is thus necessary to evaluate whether the E2 subunit vaccine can completely protect against the current prevalent strains in the field. An ideal new generation of vaccine should be able to maintain the high protective efficiency of MLV and overcome the problem of antigenic variations while allowing for DIVA.

Intra-host variation structure of classical swine fever virus NS5B in relation to antiviral therapy

Classical swine fever (CSF) is one of most important diseases of the Suidea with severe social economic consequences in case of outbreaks. Antivirals have been demonstrated, in recent publications, to be an interesting alternative method of fighting the disease. However, classical swine fever virus is an RNA virus which presents a challenge as intra-host variation and the error prone RNA dependent RNA polymerase (RdRp) could lead to the emergence/selection of resistant variants hampering further treatment. Therefore, it was the purpose of this study to investigate the intra-host variation of the RdRp gene, targeted by antivirals, in respect to antiviral treatment. Using the non-unique nucleotide changes, a limited intra-host variation was found in the wild type virus with 2 silent and 2 non-synonymous sites. This number shifted significantly when an antiviral resistant variant was analyzed. In total 22nt changes were found resulting in 14 amino acid changes whereby each genome copy contained at least 2 amino-acid changes in the RdRp. Interestingly, the frequency of the mutations situated in close proximity to a region involved in antiviral resistance in CSFV and bovine viral diarrhea virus (BVDV) was elevated compared to the other mutations. None of the identified mutations in the resistant variant and which could potentially result in antiviral resistance was present in the wild type virus as a non-unique mutation. In view of the spectrum of mutations identified in the resistance associated region and that none of the resistance associated mutations reported for another strain of classical swine fever for the same antiviral were observed in the study, it can be suggested that multiple mutations confer resistance to some degree. Although the followed classical approach allowed the analysis the RdRp as a whole, the contribution of unique mutations to the intra-host variation could not be completely resolved. There was a significant difference in de number of unique mutations found between: 1/wild type virus and the antiviral resistant variant and 2/between both and the number to be expected from the error rate of the RT-PCR process. This indicates that the some of the unique mutations contributed to the intra-host variation and that the antiviral pressure also shifted this pattern. This is important as one of the non-synonymous mutations found in the resistant variant and which was located in the antiviral resistance associated region, was present in the wild type virus as a unique mutation. The findings presented in this study not only show the importance of intra-host variation analysis but also warrants further research certainly in view of the potential inclusion of antivirals in a control/eradication strategy.

Challenge of pigs with classical swine fever viruses after C-strain vaccination reveals remarkably rapid protection and insights into early immunity

Pre-emptive culling is becoming increasingly questioned as a means of controlling animal diseases, including classical swine fever (CSF). This has prompted discussions on the use of emergency vaccination to control future CSF outbreaks in domestic pigs. Despite a long history of safe use in endemic areas, there is a paucity of data on aspects important to emergency strategies, such as how rapidly CSFV vaccines would protect against transmission, and if this protection is equivalent for all viral genotypes, including highly divergent genotype 3 strains. To evaluate these questions, pigs were vaccinated with the Riemser® C-strain vaccine at 1, 3 and 5 days prior to challenge with genotype 2.1 and 3.3 challenge strains. The vaccine provided equivalent protection against clinical disease caused by for the two challenge strains and, as expected, protection was complete at 5 days post-vaccination. Substantial protection was achieved after 3 days, which was sufficient to prevent transmission of the 3.3 strain to animals in direct contact. Even by one day post-vaccination approximately half the animals were partially protected, and were able to control the infection, indicating that a reduction of the infectious potential is achieved very rapidly after vaccination. There was a close temporal correlation between T cell IFN-γ responses and protection. Interestingly, compared to responses of animals challenged 5 days after vaccination, challenge of animals 3 or 1 days post-vaccination resulted in impaired vaccine-induced T cell responses. This, together with the failure to detect a T cell IFN-γ response in unprotected and unvaccinated animals, indicates that virulent CSFV can inhibit the potent antiviral host defences primed by C-strain in the early period post vaccination.

A study on the applicability of implantable microchip transponders for body temperature measurements in pigs

Background

The applicability of an electronic monitoring system using microchip transponders for measurement of body temperatures was tested in 6-week-old conventional Danish weaners infected with classical swine fever virus (CSFV). Subcutaneous tissue temperatures obtained by the implantable transponders were compared with rectal temperatures, recorded by a conventional digital thermometer.

Methods

In a preliminary study, transponders were inserted subcutaneously at 6 different positions of the body of 5 pigs. The transponders positioned by the ear base provided the best correlation to rectal temperature. To test the stability of the monitoring system in a larger group of pigs, transponders were therefore inserted by the left ear base in a subsequent infection experiment with 30 pigs.

Results

Generally, the microchip transponders measured a subcutaneous tissue temperature, which was about 1°C lower than the rectal temperature. However, a simple linear relationship between the measures of the two methods was found.

Conclusions

Our study showed that the tested body monitoring system may represent a promising tool to obtain an approximate correlate of body temperatures in groups of pigs. In contrast, however, the tested system did not constitute a suitable tool to measure body temperatures of individual animals in the present pig infection experiment.

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.

Rational design of a classical swine fever C-strain vaccine virus that enables the differentiation between infected and vaccinated animals

The C-strain of the classical swine fever virus (CSFV) is considered the gold standard vaccine for the control of CSF. This vaccine, however, does not enable the serological differentiation between infected and vaccinated animals (DIVA). Consequently, its use can impose severe trade restrictions. The immunodominant and evolutionarily conserved A-domain of the E2 structural glycoprotein is an important target in CSFV-specific ELISAs. With the ultimate aim to render the C-strain suitable as a DIVA vaccine, mutations were introduced that were expected to dampen the immunogenicity of the A-domain. In the first of two approaches, the feasibility of shielding the A-domain by N-linked glycans was evaluated, whereas in the second approach C-strain mutants were created with targeted deletions in the A-domain. Analysis of the antibody responses elicited in rabbits suggested that shielding of the A-domain by an N-linked glycan had a minor effect on the immune response against the A-domain, whereas a targeted deletion of only a single amino acid severely dampened this response. C-strain mutants with larger deletions were highly debilitated and incapable of sustained growth in vitro. By providing the viruses with the opportunity to increase their fitness by mutation, a mutant was rescued that found a way to compensate for the imposed fitness cost. Most of the identified mutations occurred in several independently evolved viruses, demonstrating parallel evolution. By virtue of this compensatory evolution, a well replicating and genetically stable C-strain mutant was produced that can be serologically differentiated from wildtype CSFV. The findings provide the molecular basis for the development of a novel, genetically stable, live attenuated CSF DIVA vaccine.

Effect of strain and inoculation dose of classical swine fever virus on within-pen transmission

To improve the understanding of the dynamics and options for control of classical swine fever (CSF), more quantitative knowledge is needed on virus transmission. In this study, virus excretion and within-pen transmission of a strain of low, moderate and high virulence were quantified. Furthermore, the effect of inoculation dose on excretion and transmission were studied. The transmission was quantified using a stochastic susceptible-exposed-infectious-recovered (SEIR) model. Five transmission trials were conducted with ten pigs each. In each trial, three pigs were inoculated with the low virulent strain Zoelen, a low (10(2) TCID(50)), middle (10(3.5) TCID(50)), or high dose (10(5) TCID(50)) of the moderately virulent strain Paderborn, or the highly virulent strain Brescia. The other seven pigs in each trial served as contact pigs. None of the pigs inoculated with the low dose of the Paderborn strain were infected. When it was assumed that the infectiousness of the pigs coincided with virus isolation positive oropharyngeal fluid and/or faeces, no significant differences in transmission rate beta and basic reproduction ratio R(0) between the high inoculation dose of the Paderborn strain (beta= 1.62/day, R(0) = 35.9) and the Brescia strain (beta= 2.07/day, R(0)= 17.5) were observed. When the middle dose of the Paderborn strain was used for inoculation, the beta (5.38/day) was not significantly higher than the Brescia strain or the high inoculation dose of the Paderborn strain, but the R(0) (148) was significantly higher. Infection with the Zoelen strain resulted in a significantly lower beta and R(0) (beta= 0/day, R(0) = 0) than the other strains.

Early onset and long lasting protection in pigs provided by a classical swine fever E2-vaccine candidate produced in the milk of goats

For vaccination against classical swine fever virus (CSFV), it is strongly desirable to induce a rapid and long lasting protection. At present, only live attenuated CSFV vaccines have shown early onset of protection, differing with the recombinant subunit-based vaccines reported so far. Recently, a new vaccine formulation based on E2 envelope viral glycoprotein produced in the milk of goats (E2his) has been shown to induce a highly protective response in pigs against CSFV infection. Pigs immunized with a single dose of this vaccine candidate, formulated as a water-in oil emulsion, elicited an effective response against CSF as early as 7 days post-vaccination. No severe CSF clinical signs were observed and no animals died although the challenge dose was 10(5)PDL(50) of a highly pathogenic CSFV strain. Noticeably, this response completely prevented CSFV infection in pigs when they were challenged under the same conditions 2 weeks after a single dose of the recombinant E2his vaccine formulation. A schedule consisting of a primary immunization with the same vaccine candidate, followed by a booster dose 2 weeks later induced a highly protective response against CSFV infection for as long as 9 months post-vaccination. These promising results demonstrate by far the feasibility of using the E2his-based vaccine in regional programs for preventing and controlling CSF.

Yeast-expressed classical swine fever virus glycoprotein E2 induces a protective immune response

Classical swine fever (CSF) is an economically important swine disease worldwide. The glycoprotein E2 of classical swine fever virus (CSFV) is a viral antigen that can induce a protective immune response against CSF. A recombinant E2 protein was constructed using the yeast Pichia pastoris expression system and evaluated for its vaccine efficacy. The yeast-expressed E2 (yE2) was shown to have N-linked glycosylation and to form homodimer molecules. Four 6-week-old specified-pathogen-free (SPF) piglets were intramuscularly immunized with yE2 twice at 3-week intervals. All yE2-vaccinated pigs could mount an anamnestic response after booster vaccination with neutralizing antibody titers ranging from 1:96 to 1:768. Neutralizing antibody titers at 10 weeks post booster vaccination ranged from 1:16 to 1:64. At this time, the pigs were subjected to challenge infection with a dose of 1x10(5)TCID(50) (50% tissue culture infective dose) virulent CSFV strain. At 1 week post challenge infection, all of the yE2-immunized pigs were alive and without symptoms or signs of CSF. Neutralizing antibody titers at this time ranged from 1:4,800 to 1:12,800 and even to 1:51,200 one week later. In contrast, the control pigs continuously exhibited signs of CSF and had to be euthanized because of severe clinical symptoms at 6 days post challenge infection. All of the yE2-vaccinated pigs were E(rns) antibody negative and had seroconverted against E(rns) by post challenge day 11, suggesting that yE2 is a potential DIVA (differentiating infected from vaccinated animals) vaccine. The yeast-expressed E2 protein retains correct immunogenicity and is able to induce a protective immune response against CSFV infection.

Virulence of classical swine fever virus isolates from Europe and other areas during 1996 until 2007

Classical Swine Fever (CSF) has caused several outbreaks in EU Member States with grave economic consequences. Several times the diagnosis of CSF was made too late partially due to non-specific clinical signs which did not raise suspicion for CSF. Virulence of CSF virus isolates (CSFV) still remains a subject of discussion and speculation as sufficient knowledge is still not available. Six uncharacterised CSFV isolates from 1996 to 2007 were assessed in animal experiments for their clinical virulence in order to broaden the knowledge about circulating CSFV and thereby assist disease eradication. A clinical (CS) and pathological score was applied and further extended by additional parameters to a modified CS (mCS) including case fatality, antibody production and leukocyte count. The unknown CSFV isolates could be classified as moderately or highly virulent. The inclusion of additional parameters, especially case fatality, into the mCS gave a more reliable classification of virulence, proving that there are clinical signs and laboratory parameters of blood which can be recognised. Therefore a subclinical course of infection is unlikely, especially in weaner pigs.

Proof of concept for the reduction of classical swine fever infection in pigs by a novel viral polymerase inhibitor

5-[(4-Bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP) is a representative of a class of imidazopyridines with potentin vitroantiviral activity against pestiviruses including classical swine fever virus (CSFV). This study analysed whether the lead compound, BPIP, was able to reduce virus replication in infected piglets. The compound, administered in feed, was readily bioavailable and was well tolerated. Eight specific-pathogen-free pigs received a daily dose of 75 mg kg−1(mixed in feed) for a period of 15 consecutive days, starting 1 day before infection with the CSFV field isolate Wingene. BPIP-treated pigs developed a short, transient viraemia (one animal remained negative) and leukopenia (three animals did not develop leukopenia). Virus titres at peak viraemia (7 days post-infection) were markedly lower (∼1000-fold) than in untreated animals (P=0.00005) and the viral genome load in blood was also significantly lower (P≤0.001) in drug-treated animals than in untreated animals over the entire experiment. At the end of the experiment (day 33), no infectious virus was detectable in the tonsils of BPIP-treated animals, although low levels of viral RNA were detected. The inability to isolate infectious virus from the tonsils indicates that the risk of a persistent CSFV infection is negligible. Further optimization of the antiviral potency and bioavailability of this lead compound may result in molecules completely suppressing virus replication. A potent antiviral could potentially be used as a primary control measure against virus spread in case of an outbreak, in addition to present countermeasures. This study provides the first proof of concept for the prophylaxis/treatment of CSFV infection in pigs.

Development of a reverse transcription multiplex real-time PCR for the detection and genotyping of classical swine fever virus

A reverse transcription multiplex real-time PCR (RT-MRT-PCR) was developed for rapid detection and genotyping of classical swine fever virus (CSFV). The universal primers and specific TaqMan probes for each of the three genotypes, genotypes 1, 2, and 3, were designed within the 3′-UTR of the CSFV. Non-CSFV swine virus and clinical samples from specific pathogen-free (SPF) pigs were both demonstrated to be CSFV-negative by RT-MRT-PCR. The diagnostic sensitivity of RT-MRT-PCR was determined to be 1 viral copy/μl for each genotype of standard plasmid. For the analytical sensitivity experiment, 100 samples of 14 CSFV genotype 1 strains and 86 samples from CSFV outbreak farms were all detected as CSFV-positive by RT-MRT-PCR, and the genotype results were consistent with the results of sequencing from a previous study. The intra-assay and inter-assay variations of RT-MRT-PCR were below 3% in all experiments. The sensitivity of RT-MRT-PCR was the same as the reverse transcription nested PCR (RT-nPCR) and higher than reverse transcription PCR (RT-PCR) and viral isolation from clinical samples. This assay was used further to evaluate the duration of viremia of wild-type CSFV in vaccinated exposed pigs. The results indicated that pigs vaccinated with the E2 subunit vaccine had longer viremia than pigs given the C-strain vaccine, which is compatible with the findings of previous studies. Thus, the new RT-MRT-PCR is a rapid, reproducible, sensitive, and specific genotyping tool for CSFV detection.

Mucosal or systemic administration of rE2 glycoprotein antigen loaded PLGA microspheres

We have evaluated the ability of recombinant E2 antigen, as a surfactant free formulation of poly (D,L-lactide-co-glycolide) (PLGA) microspheres, to elicit a systemic immune response after administration by mucosal routes (oral and nasal) in comparison to intramuscular route. The sequence encoding a truncated E2 glycoprotein of the classical swine fever virus (CSFV) was expressed in insect cells following infection with recombinant baculovirus, as a His-tagged recombinant antigen. The recombinant E2 glycoprotein (rE2) antigen was co-encapsulated with rabbit serum albumin (RSA) as a protein stabilizer. rE2/RSA loaded PLGA microspheres, with a mean diameter of 4 microm were obtained by a water in oil in water solvent extraction method (w/o/w). Rabbits were immunized with 10 microg of rE2 formulated in PLGA microspheres administrated by three different routes (oral, nasal and intramuscular). After 60 days, each rabbit in all three groups was challenge with 5 microg of rE2 glycoprotein solution by intradermal administration. Blood samples were collected weekly for 90 days and specific rE2 antigen antibodies measured. This work showed that rE2 antigen loaded microspheres was able to initiate an immune response. The intradermal challenge after nasal and oral administration had a clear boost effect on the systemic immune response. Moreover, the response after nasal administration was more intense and less variable than oral route. In conclusion, these data demonstrate a high potential of rE2 loaded PLGA microspheres for their use as a mucosal subunit vaccine.

Modelling the effectiveness and risks of vaccination strategies to control classical swine fever epidemics

In a recent update of the Dutch contingency plan for controlling outbreaks of classical swine fever (CSF), emergency vaccination is preferred to large-scale pre-emptive culling. This policy change raised two questions: can emergency vaccination be as effective as pre-emptive culling, and what are the implications for showing freedom of infection? Here, we integrate quantitative information available on CSF virus transmission and vaccination effects into a stochastic mathematical model that describes the transmission dynamics at the level of animals, farms and livestock areas. This multilevel approach connects individual-level interventions to large-scale effects. Using this model, we compare the performance of five different control strategies applied to hypothetical CSF epidemics in The Netherlands and, for each of these strategies, we study the properties of three different screening scenarios to show freedom of infection. We find that vaccination in a ring of 2 km radius around a detected infection source is as effective as ring culling in a 1 km radius. Feasible screening scenarios, adapted to the use of emergency vaccination, can reduce the enhanced risks of (initially) undetected farm outbreaks by targeting vaccinated farms. Altogether, our results suggest that emergency vaccination against CSF can be equally effective and safe as pre-emptive culling.