Molecular epidemiology of a large classical swine fever epidemic in the European Union in 1997-1998

Identification of neutralizing epitopes on the D/A domain of the E2 glycoprotein of classical swine fever virus

Classical swine fever virus (CSFV) shares high antigenic homology with other members of the genus Pestivirus. Because several pestivirus species can also infect swine, eliciting cross-reactive antibodies, it is important to define CSFV-specific epitopes for the differential diagnosis of classical swine fever (CSF) by serology. For this purpose, epitope mapping of seven monoclonal antibodies (mAbs), recognizing sites on the D/A domain of glycoprotein E2, was performed using recombinant expressed antigenic domains and mutants of E2, as well as an overlapping peptide library. Three CSFV-specific epitopes, i.e., 780-IEEMGDDFGFGLCPF-794, 810-NGSAFYLVCPIGWTG-824, and 846-REKPF-850, were identified within the D/A domain of E2. Site-directed mutagenesis further confirmed that residues 783-MGD-785, 789-FGLCPF-794, 813-AFYLVCPIGWTG-824, and 846-REK-848 were critical residues in these regions. In addition, a F789S difference within the epitope 780-IEEMGDDFGFGLCPF-794 was responsible for the absence of binding of two mAbs to the E2 protein of the live attenuated CSFV vaccine strain Riems. Structural modeling revealed that, the three epitopes are located near each other, suggesting that they may form a more complex conformational epitope on the D/A domain in vivo. Six of the mAbs neutralized viruses of diverse genotypes, indicating that the target epitopes are involved in virus interaction with cells. The binding of CSFV to cells was significantly reduced after pre-incubation with either truncated E2 proteins comprising the D/A domain or with the CSFV-specific mAbs targeting the domain D/A. These epitopes identified on the D/A domain are important targets for virus neutralization that might be involved in the early steps of CSFV infection. These findings reveal potential candidates for improving the differential diagnosis of pestiviruses by serology.

In vivo characterization of the superior fitness of classical swine fever virus genotype 2.1 to genotype 3.4

Classical swine fever (CSF), caused by classical swine fever virus (CSFV), is a highly contagious disease in pigs. In Taiwan, the emerging genotype 2.1 (G2.1) CSFV caused sporadic outbreaks in 1994 and replaced the previous G3.4 CSFV in the field. The shift of CSFV genotypes to G2 CSFV was also observed in several CSFV-affected countries. The present study aimed to explore the mechanism of the genotype shift of CSFV. Two groups of specific pathogen-free (SPF) pigs were first inoculated with either G2.1 or G3.4 CSFV (single-inoculated group) and housed together with naïve SPF pigs (cohabitating group). The results showed that peak viremia, viral loads in blood and tissues, and viral shedding of G2.1 were consistently higher than those of G3.4 CSFV in single-inoculated and cohabitating pigs. The phenomenon of superinfection exclusion (SIE), characterized by the prevention of secondary infection by a primary infection, was readily observed in CSFV single-inoculated pigs. Interestingly, coinfection of both genotypes of CSFV was observed in 3 out of 4 cohabitating pigs, while only one pig was infected with G2.1 CSFV alone. These findings suggest that the genetic shift in CSFV in the field may be in part the consequence of SIE.

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.

Production of Bivalent Subunit Vaccine for Porcine via 2A-Like Sequence in Baculovirus Expression Vector System

Classical swine fever virus (CSFV) and porcine circovirus type 2 (PCV2) have caused severe diseases in swine populations worldwide. Here, a polycistronic baculovirus vector was developed to express a bivalent vaccine, consisting of the CSFV-E2 and PCV2-Cap protein, and an immunomodulator protein derived from the Flammulina velutipes, FVE-FIP, as well as the selection marker, green fluorescent protein. The simultaneous expression of the CSFV-E2 and PCV2-Cap protein was mediated by the 2A-like sequence derived from the Perina nuda virus (PnV), while the expression of the FVE-FIP was driven by the internal ribosome entry site (IRES) element derived from the Rhophalosipum padi virus (RhPV). The Western blot analysis result suggested that the CSFV-E2, PCV2-Cap, and FVE-FIP protein were successfully co-expressed by the infected Spodoptera frugiperda IPBL-Sf21 (Sf21) cell line. The extracted cell lysate containing all three recombinant proteins was administered to Balb/C mice with or without the supplementation of Freund’s adjuvant. The ELISA analysis of the serum collected from all the immunized groups showed detectable antibodies against CSFV-E2 and PCV2-Cap. Furthermore, the immunized group without the adjuvant supplementation demonstrated a similar level of antibodies to the group with adjuvant supplementation, suggesting the efficiency of the FVE-FIP in enhancing the immune response. These results demonstrated the polycistronic baculovirus vector could be employed to develop bivalent vaccines for pigs.

Eradication of Bovine Viral Diarrhoea (BVD) in Cattle in Switzerland: Lessons Taught by the Complex Biology of the Virus

Bovine viral diarrhoea virus (BVDV) and related ruminant pestiviruses occur worldwide and cause considerable economic losses in livestock and severely impair animal welfare. Switzerland started a national mandatory control programme in 2008 aiming to eradicate BVD from the Swiss cattle population. The peculiar biology of pestiviruses with the birth of persistently infected (PI) animals upon in utero infection in addition to transient infection of naïve animals requires vertical and horizontal transmission to be taken into account. Initially, every animal was tested for PI within the first year, followed by testing for the presence of virus in all newborn calves for the next four years. Prevalence of calves being born PI thus diminished substantially from around 1.4% to <0.02%, which enabled broad testing for the virus to be abandoned and switching to economically more favourable serological surveillance with vaccination being prohibited. By the end of 2020, more than 99.5% of all cattle farms in Switzerland were free of BVDV but eliminating the last remaining PI animals turned out to be a tougher nut to crack. In this review, we describe the Swiss BVD eradication scheme and the hurdles that were encountered and still remain during the implementation of the programme. The main challenge is to rapidly identify the source of infection in case of a positive result during antibody surveillance, and to efficiently protect the cattle population from re-infection, particularly in light of the endemic presence of the related pestivirus border disease virus (BDV) in sheep. As a consequence of these measures, complete eradication will (hopefully) soon be achieved, and the final step will then be the continuous documentation of freedom of disease.

Quantitative risk assessment of the African swine fever introduction into the Republic of Korea via legal import of live pigs and pig products

There are several routes of African swine fever (ASF) introduction into a country. Among the possible routes of entry, quarantine policies determine the possibility of introduction by legal import of live pigs and pig products. This study aimed at assessing the probability of ASF introduction through legal import of live pigs and pig products during the high-risk period (HRP) using a quantitative stochastic approach during 2009-2018. The result indicates that the mean annual probability of ASF introduction by legal import of live pig was 1.58 × 10^-7 (1.52~1.67 × 10^-7 95% CI). The mean annual probability by legal import of pig products was 1.59 × 10^-10 (1.55~1.64 × 10^-10 95% CI), of which Poland assumed 87.9% of the mean annual risk. The current import quarantine policy of Korean government may be enough to block the release of the virus via legal import of live pigs and pig products, and it should be continually enforced. This result can help to elucidate source of infection and to minimize the catastrophic consequences of the potential ASF reintroduction into South Korea by designing risk mitigation strategies such as risk-based selection of routes to be assessed and prevented and decreased exposure possibility by increased control of food waste and swill feeding practices.

Transmission of African swine fever in China Through Legal Trade of Live Pigs

The African swine fever virus (ASFV) was first reported in China on 3 August 2018, which subsequently triggered a severe epidemic that spreads across the country. While the ASFV has numerous underlying transmission paths in China, this study primarily assessed the possibility of ASFV transmission through the legal animal husbandry trade. The reason for this is that, historically, this transmission path is one of the critical contacts for exotic diseases to access disease-free areas. This study employed a stochastic model to assess the monthly possibility for ASFV entering respective Chinese provinces. The results of this model suggest that the risk of ASFV transmission though the legal live-pig trade is highest in the southeastern regions of China. Vulnerable regions centred around Zhejiang, Jiangsu and Anhui provinces, especially throughout the months of January and December. Liaoning province contributes most to transmission risk with 46.7% of the overall annual risk. This study quantified the risk of ASFV spread in China related to the legal trade of pigs and provides detailed and new information for the development of ASFV monitoring and control plans in China and other countries who also face the challenge of ASFV.

A classical swine fever virus E2 fusion protein produced in plants elicits a neutralizing humoral immune response in mice and pigs

Classical swine fever (CSF) is one of the most important viral diseases of swine worldwide. Although live or attenuated virus vaccines have been used to control CSFV, it is difficult to distinguish vaccinated pigs from infected pigs; this leads to restrictions on import and export. Subunit vaccines based on the CSFV E2 glycoprotein have been developed using baculovirus or insect cell systems, but some weaknesses remain. Here, we describe production of an E2 recombinant protein using a Nicotiana benthamiana plant expression system. To do this, we took advantage of the ability of the swine Fc domain to increase solubility and stability of the fusion protein and to strengthen immune responses in target animals. N. benthamiana expressed high amounts of pFc2-fused E2 proteins, which were isolated and purified by affinity chromatography to yield a high pure recombinant protein in a cost-effective manner. Native-polyacrylamide gel electrophoresis and size exclusion chromatography confirmed that the pmE2:pFc2 fusion exists as a multimer rather than as a dimer. Injection of recombinant pmE2 protein into mice or piglets generated anti-pmE2 antibodies with efficient neutralizing activity against CSFV. These results suggest that a purified recombinant E2 protein produced in N. benthamiana generates high titers of neutralizing antibodies in vivo; as such, the protein could be developed as a subunit vaccine against CSFV.

In Vivo Demonstration of the Superior Replication and Infectivity of Genotype 2.1 with Respect to Genotype 3.4 of Classical Swine Fever Virus by Dual Infections

In Taiwan, the prevalent CSFV population has shifted from the historical genotype 3.4 (94.4 strain) to the newly invading genotype 2.1 (TD/96 strain) since 1996. This study analyzed the competition between these two virus genotypes in dual infection pigs with equal and different virus populations and with maternally derived neutralizing antibodies induced by a third genotype of modified live vaccine (MLV), to simulate that occurring in natural situations in the field. Experimentally, under various dual infection conditions, with or without the presence of maternal antibodies, with various specimens from blood, oral and fecal swabs, and internal organs at various time points, the TD/96 had consistently 1.51-3.08 log higher loads than those of 94.4. A second passage of competition in the same animals further widened the lead of TD/96 as indicated by viral loads. The maternally derived antibodies provided partial protection to both wild type CSFVs and was correlated with lower clinical scores, febrile reaction, and animal mortality. In the presence of maternal antibodies, pigs could be infected by both wild type CSFVs, with TD/96 dominating. These findings partially explain the CSFV shift observed, furthering our understanding of CSFV pathogenesis in the field, and are helpful for the control of CSF.

Transboundary spread of pig diseases: the role of international trade and travel

As globalization increases the interconnectedness between nations, economies, and industries, the introduction of diseases will continue to remain a prominent threat to the livestock sector and the trade of animals and animal products, as well as the livelihoods of farmers, food security and public health. The global pig sector, with its size and dichotomy between production type and biosecurity level, is particularly vulnerable to the transmission of transboundary animal diseases such as African and classical swine fever, foot and mouth disease, or porcine reproductive and respiratory syndrome. All of the above pose a constant threat to swine health, mainly as a result of both formal and informal international trade.Inspired in the risk assessment methodology, this paper classifies and provides an overview of the different pig disease introduction and exposure pathways, illustrated with abundant examples. Introduction pathways are classified as formal international trade (by product), informal international trade (by product), and spread through fomites. Formal trade of pigs and pork products is regulated by legislation and measures protecting animal populations from exotic diseases. Much more difficult to control is the transboundary swine disease transmission originating through informal trade, which entails illegal smuggling, but also the informal cross-border transfer of animals and products for personal use or within informal market chains. Meat products are most commonly mentioned, although fomites have also played a role in some cases, with live pigs, being more difficult to smuggle playing a role less frequently. The main exposure pathways are also described with the oral route playing a prominent role.Risk assessments can aid in the identification of pathways of pathogen introduction and exposure. However, quantitative information on informal disease introduction pathways remains very scarce and often incomplete, making it difficult to estimate the actual magnitudes of risks. Nevertheless, this knowledge is deemed essential to set up risk based awareness, prevention and surveillance programs that correspond to reality.

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.

A Review of Classical Swine Fever Virus and Routes of Introduction into the United States and the Potential for Virus Establishment

Classical swine fever (CSF) is caused by CSF virus (CSFV) which can be the source of substantial morbidity and mortality events in affected swine. The disease can take one of several forms (acute, chronic, or prenatal) and depending on the virulence of the inoculating strain may result in a lethal infection irrespective of the form acquired. Because of the disease-free status of the United States and the high cost of a viral incursion, a summary of US vulnerabilities for viral introduction and persistence is provided. The legal importation of live animals as well as animal products, byproducts, and animal feed serve as a potential route of viral introduction. Current import regulations are described as are mitigation strategies that are commonly utilized to prevent pathogens, including CSFV, from entering the US. The illegal movement of suids and their products as well as an event of bioterrorism are both feasible routes of viral introduction but are difficult to restrict or regulate. Ultimately, recommendations are made for data that would be useful in the event of a viral incursion. Population and density mapping for feral swine across the United States would be valuable in the event of a viral introduction or spillover; density data could further contribute to understanding the risk of infection in domestic swine. Additionally, ecological and behavioral studies, including those that evaluate the effects of anthropogenic food sources that support feral swine densities far above the carrying capacity would provide invaluable insight to our understanding of how human interventions affect feral swine populations. Further analyses to determine the sampling strategies necessary to detect low levels of antibody prevalence in feral swine would also be valuable.

Deciphering the emergence, genetic diversity and evolution of classical swine fever virus

Classical swine fever (CSF) is one of the most important infectious diseases causing significant economic losses. Its causal agent, CSF virus (CSFV), is a member of the Pestivirus genus included into the Flaviviridae family. Previous molecular epidemiology studies have revealed the CSFV diversity is divided into three main genotypes and different subgenotypes. However, the classification system for CSFV has not yet been harmonized internationally. Similarly, the phylogeny and evolutionary dynamics of CSFV remain unclear. The current study provides novel and significant insights into the origin, diversification and evolutionary process of CSFV. In addition, the best phylogenetic marker for CSFV capable of reproducing the same phylogenetic and evolutionary information as the complete viral genome is characterized. Also, a reliable cut-off to accurately classify CSFV at genotype and subgenotype levels is established. Based on the time for the most recent common ancestor (tMRCA) reconstruction and cophylogenetic analysis, it was determined that CSFV emerged around 225 years ago when the Tunisian Sheep Virus jumped from its natural host to swine. CSFV emergence was followed by a genetic expansion in three main lineages, driven by the action of positive selection pressure and functional divergence, as main natural forces.

Phylogenetic analysis of Classical swine fever virus from archival formalin fixed clinical tissues reveals vietnamese origin of the isolates

Detection of Classical swine fever virus (CSFV) nucleic acid in archival formalin fixed tissue samples and their use for phylogenetic analysis was investigated. Ten samples were examined for the presence of CSFV nucleic acid by reverse transcriptase polymerase chain reaction (RT-PCR) amplification of 5'UTR and E2 gene. RT-PCR was found positive for 5'UTR fragment in eight samples while only one tissue samples showed amplification for E2 gene target fragment. For molecular epidemiology of the disease, 5'UTR PCR product of sample from Darbhanga (Bihar), was cloned and sequenced. The sequence was compared with the sequences available in database. The phylogenetic analysis reveals that the isolate belongs to subgroup 2.2 sharing 98.7% nucleotide identities with Vietnamese isolate (CaTh05-1, AB252170), indicating towards the possible origin of genogroup 2.2 CSFV isolates involved in the outbreak from Vietnam. From the study, it can be concluded that the tissue samples collected and stored in buffer formalin for years can be used to detect CSFV nucleic acid. Results are also suggestive of that the 5'UTR region of genome is more suitable target for RT-PCR based detection of CSFV in archival formalin fixed specimens. The study also indicates the potential of archival formalin fixed tissues for molecular epidemiology and genotyping of the CSF virus.

Classical Swine Fever-An Updated Review

Classical swine fever (CSF) remains one of the most important transboundary viral diseases of swine worldwide. The causative agent is CSF virus, a small, enveloped RNA virus of the genus Pestivirus. Based on partial sequences, three genotypes can be distinguished that do not, however, directly correlate with virulence. Depending on both virus and host factors, a wide range of clinical syndromes can be observed and thus, laboratory confirmation is mandatory. To this means, both direct and indirect methods are utilized with an increasing degree of commercialization. Both infections in domestic pigs and wild boar are of great relevance; and wild boars are a reservoir host transmitting the virus sporadically also to pig farms. Control strategies for epidemic outbreaks in free countries are mainly based on classical intervention measures; i.e., quarantine and strict culling of affected herds. In these countries, vaccination is only an emergency option. However, live vaccines are used for controlling the disease in endemically infected regions in Asia, Eastern Europe, the Americas, and some African countries. Here, we will provide a concise, updated review on virus properties, clinical signs and pathology, epidemiology, pathogenesis and immune responses, diagnosis and vaccination possibilities.

Competitive replication kinetics and pathogenicity in pigs co-infected with historical and newly invading classical swine fever viruses

Classical swine fever (CSF), an economically important and highly contagious disease of pigs, is caused by classical swine fever virus (CSFV). In Taiwan, CSFVs from field outbreaks belong to two distinct genotypes. The historical genotype 3.4 dominated from the 1920s to 1996, and since 1996, the newly invading genotype 2.1 has dominated. To explain the phenomenon of this virus shift in the field, representative viruses belonging to genotypes 2.1 and 3.4 were either inoculated alone (single infection) or co-inoculated (co-infection), both in vivo and in vitro, to compare the virus replication and pathogenesis. In pigs co-infected with the genotype 2.1 TD/96/TWN strain and the genotype 3.4 94.4/IL/94/TWN strain, the newly invading genotype 2.1 was detected earlier in the blood, oral fluid, and feces, and the viral loads were consistently and significantly higher than that of the historical genotype 3.4. In cell cultures, the ratio of secreted virus to cell-associated virus of the genotype 2.1 strain was higher than that of the genotype 3.4 strain. This study is the first to demonstrate a possible explanation of virus shift in the field, wherein the newly invading genotype 2.1 replicates more efficiently than did genotype 3.4 and outcompetes the replication and pathogenicity of genotype 3.4 in pigs in the field.

Genetic diversity of subgenotype 2.1 isolates of classical swine fever virus

As the causative agent of classical swine fever, the economically devastating swine disease worldwide, classical swine fever virus (CSFV) is currently classified into the 11 subgenotypes, of which subgenotype 2.1 is distributed worldwide and showing more genetic diversity than other subgenotypes. Prior to this report, subgenotype 2.1 was divided into three sub-subgenotypes (2.1a-2.1c). To further analyze the genetic diversity of CSFV isolates in China, 39 CSFV isolates collected between 2004 and 2012 in two Chinese provinces Guangxi and Guangdong were sequenced and subjected to phylogenetic analysis together with reference sequences retrieved from GenBank. Phylogenetic analyses based on the 190-nt and/or 1119-nt full length E2 gene fragments showed that current CSFV subgenotype 2.1 virus isolates in the world could be divided into 10 sub-subgenotypes (2.1a-2.1j) and the 39 isolates collected in this study were grouped into 7 of them (2.1a-2.1c and 2.1g-2.1j). Among the 10 sub-subgenotypes, 2.1d-2.1j were newly identified. Sub-subgenotype 2.1d isolates were circulated only in India, however the rest 9 sub-subgenotypes were from China with some of them closely related to isolates from European and neighboring Asian countries. According to the temporal and spatial distribution of CSFV subgenotype 2.1 isolates, the newly classified 10 sub-subgenotypes were further categorized into three groups: dominant sub-subgenotype, minor sub-subgenotype and silent sub-subgenotype, and each sub-subgenotype can be found only in certain geographical areas. Taken together, this study reveals the complex genetic diversity of CSFV subgenotype 2.1 and improves our understanding about the epidemiological trends of CSFV subgenotype 2.1 in the world, particularly in China.

Genetic variability and distribution of Classical swine fever virus

Classical swine fever is a highly contagious disease that affects domestic and wild pigs worldwide. The causative agent of the disease is Classical swine fever virus (CSFV), which belongs to the genus Pestivirus within the family Flaviviridae. On the genome level, CSFV can be divided into three genotypes with three to four sub-genotypes. Those genotypes can be assigned to distinct geographical regions. Knowledge about CSFV diversity and distribution is important for the understanding of disease dynamics and evolution, and can thus help to design optimized control strategies. For this reason, the geographical pattern of CSFV diversity and distribution are outlined in the presented review. Moreover, current knowledge with regard to genetic virulence markers or determinants and the role of the quasispecies composition is discussed.

Molecular typing and phylogenetic analysis of classical swine fever virus isolates from Kerala, India

Classical swine fever (CSF) is an economically important disease of pigs caused by CSF virus (CSFV) belonging to the genus Pestivirus within the family Flaviviridae. The disease is endemic in many countries including India. A comprehensive study was carried out to assess the type of CSFV circulating in the South Indian state of Kerala. During the period 2013-2014, clinical samples were collected from 19 suspected CSF outbreaks of domestic pigs in different districts of Kerala. The samples were tested using nested reverse transcription PCR (RT-PCR) targeting the E2 gene and RT-PCR for 5'UTR of the virus. Partial 5' UTR and E2 gene regions of six CSFV isolates were sequenced. Phylogenetic analysis revealed that all the CSFV isolates belonged to subgroup 2.2. The isolates showed close resemblance to the other CSFV isolates circulating in India. It was also observed that the CSFV viruses from Kannur district were distinct from those circulating in the other districts as evidenced by their divergence from other Kerala isolates in the phylogenetic tree. Close relationship was seen to the CSFV isolates from South East Asian countries.

Genetic clustering of recent classical swine fever virus isolates from Karnataka, India revealed the emergence of subtype 2.2 replacing subtype 1.1

The phylogenetic analysis of 11 CSFV isolates from Karnataka, India obtained during the year 2012-13 was undertaken to obtain the most reliable genetic typing of the CSFV isolates based on E2, NS5B and 5'UTR genomic regions. The study indicated that all the 11 CSFV isolates belonged to subgroup 2.2. The most reliable classification was obtained with sequence data from the NS5B region which separated all the isolates based on the history of outbreak and geographic origin. Analysis of full length E2 amino acid sequences revealed different genetic makeup of Indian 2.2 isolates compared to 2.2 isolates from different countries. The group 2.2 viruses are gradually spreading as confirmed by frequent detection/ isolation of group 2.2 viruses in the recent years and replacing the subgroup 1.1 viruses, which were hitherto predominantly involved in CSF outbreaks in India.

Integrin β3 is required in infection and proliferation of classical swine fever virus

Classical Swine Fever (CSF) is a highly infectious fatal pig disease, resulting in huge economic loss to the swine industry. Integrins are membrane-bound signal mediators, expressed on a variety of cell surfaces and are known as receptors or co-receptors for many viruses. However, the role of integrin β3 in CSFV infection is unknown. Here, through quantitive PCR, immunofluorescence (IFC) and immunocytohistochemistry (ICC), we revealed that ST (swine testicles epithelial) cells have a prominent advantage in CSFV proliferation as compared to EC (swine umbilical vein endothelial cell), IEC (swine intestinal epithelial cell) and PK (porcine kidney epithelial) cells. Meanwhile, ST cells had remarkably more integrin β3 expression as compared to EC, IEC and PK cells, which was positively correlated with CSFV infection and proliferation. Integrin β3 was up-regulated post CSFV infection in all the four cell lines, while the CSFV proliferation rate was decreased in integrin β3 function-blocked cells. ShRNA1755 dramatically decreased integrin β3, with a deficiency of 96% at the mRNA level and 80% at the protein level. CSFV proliferation was dramatically reduced in integrin β3 constantly-defected cells (ICDC), with the deficiencies of 92.6%, 99% and 81.7% at 24 h, 48 h and 72 h post CSFV infection, respectively. These results demonstrate that integrin β3 is required in CSFV infection and proliferation, which provide a new insight into the mechanism of CSFV infection.

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.

Improved strategy for phylogenetic analysis of classical swine fever virus based on full-length E2 encoding sequences

Molecular epidemiology has proven to be an essential tool in the control of classical swine fever (CSF) and its use has significantly increased during the past two decades. Phylogenetic analysis is a prerequisite for virus tracing and thus allows implementing more effective control measures. So far, fragments of the 5´NTR (150 nucleotides, nt) and the E2 gene (190 nt) have frequently been used for phylogenetic analyses. The short sequence lengths represent a limiting factor for differentiation of closely related isolates and also for confidence levels of proposed CSFV groups and subgroups. In this study, we used a set of 33 CSFV isolates in order to determine the nucleotide sequences of a 3508-3510 nt region within the 5´ terminal third of the viral genome. Including 22 additional sequences from GenBank database different regions of the genome, comprising the formerly used short 5´NTR and E2 fragments as well as the genomic regions encoding the individual viral proteins Npro, C, Erns, E1, and E2, were compared with respect to variability and suitability for phylogenetic analysis. Full-length E2 encoding sequences (1119 nt) proved to be most suitable for reliable and statistically significant phylogeny and analyses revealed results as good as obtained with the much longer entire 5´NTR-E2 sequences. This strategy is therefore recommended by the EU and OIE Reference Laboratory for CSF as it provides a solid and improved basis for CSFV molecular epidemiology. Finally, the power of this method is illustrated by the phylogenetic analysis of closely related CSFV isolates from a recent outbreak in Lithuania.

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.

Virus inactivation by salt (NaCl) and phosphate supplemented salt in a 3D collagen matrix model for natural sausage casings

Due to possible presence and spread of contagious animal viruses via natural sausage casings the international trade in these food products is subject to veterinary and public health requirements. In order to manage these restrictions we determined the effect of casing preservation on four highly contagious viruses for livestock: foot-and-mouth-disease virus (FMDV), classical swine fever virus (CSFV), swine vesicular disease virus (SVDV) and African swine fever virus (ASFV). We used an in vitro 3D collagen matrix model in which cells, infected with the four different viruses were embedded in a bovine collagen type I gel matrix and treated with either saturated salt (NaCl) or phosphate supplemented saturated salt at four different temperatures (4, 12, 20 and 25 °C) during a period of 30 days. The results showed that all viruses were faster inactivated at higher temperatures, but that stability of the various viruses at 4 °C differed. Inactivation of FMDV in the 3D collagen matrix model showed a clear temperature and treatment effect on the reduction of FMDV titres. At 4 and 12 °C phosphate supplemented salt showed a very strong FMDV inactivation during the first hour of incubation. Salt (NaCl) only had a minor effect on FMDV inactivation. Phosphate supplemented salt treatment increased the effect temperature had on inactivation of CSFV. In contrast, the salt (NaCl) treatment only increased CSFV inactivation at the higher temperatures (20 °C and 25 °C). Also SVDV inactivation was increased by phosphate supplemented salt, but salt (NaCl) treatment only resulted in a significant decrease of SVDV titre at a few time points. The ASFV results showed that both salt (NaCl) and phosphate supplemented salt were capable to inactivate ASFV within 48 h. In contrast to the other viruses (FMDV, CSFV and SVDV), ASFV was the most stable virus even at higher temperatures. The results obtained in this in vitro model underline the efficacy of a combined treatment using phosphate supplemented salt and storage at 20 °C or higher for a period of 30 days. This treatment may therefore be useful in reducing the animal health risks posed by spread of contagious animal viruses by international trade of natural sausage casings.

Phylogenetic analysis of NS5B gene of classical swine fever virus isolates indicates plausible Chinese origin of Indian subgroup 2.2 viruses

Twenty-three CSFV isolates recovered from field outbreaks in various parts of India during 2006-2009 were used for genetic analysis in the NS5B region (409 nts). Seventeen of these were studied earlier [16] in the 5'UTR region. Phylogenetic analysis indicated the continued dominance of subgroup 1.1 strains in the country. Detailed analysis of a subgroup 2.2 virus indicated the plausible Chinese origin of this subgroup in India and provided indirect evidence of routes of CSFV movement within South East Asia region.

Antigenic analysis of classical swine fever virus E2 glycoprotein using pig antibodies identifies residues contributing to antigenic variation of the vaccine C-strain and group 2 strains circulating in China

Background

Glycoprotein E2, the immunodominant protein of classical swine fever virus (CSFV), can induce neutralizing antibodies and confer protective immunity in pigs. Our previous phylogenetic analysis showed that subgroup 2.1 viruses branched away from subgroup 1.1, the vaccine C-strain lineage, and became dominant in China. The E2 glycoproteins of CSFV C-strain and recent subgroup 2.1 field isolates are genetically different. However, it has not been clearly demonstrated how this diversity affects antigenicity of the protein.

Results

Antigenic variation of glycoprotein E2 was observed not only between CSFV vaccine C-strain and subgroup 2.1 strains, but also among strains of the same subgroup 2.1 as determined by ELISA-based binding assay using pig antisera to the C-strain and a representative subgroup 2.1 strain QZ-07 currently circulating in China. Antigenic incompatibility of E2 proteins markedly reduced neutralization efficiency against heterologous strains. Single amino acid substitutions of D705N, L709P, G713E, N723S, and S779A on C-strain recombinant E2 (rE2) proteins significantly increased heterologous binding to anti-QZ-07 serum, suggesting that these residues may be responsible for the antigenic variation between the C-strain and subgroup 2.1 strains. Notably, a G713E substitution caused the most dramatic enhancement of binding of the variant C-strain rE2 protein to anti-QZ-07 serum. Multiple sequence alignment revealed that the glutamic acid residue at this position is conserved within group 2 strains, while the glycine residue is invariant among the vaccine strains, highlighting the role of the residue at this position as a major determinant of antigenic variation of E2. A variant Simpson's index analysis showed that both codons and amino acids of the residues contributing to antigenic variation have undergone similar diversification.

Conclusions

These results demonstrate that CSFV vaccine C-strain and group 2 strains circulating in China differ in the antigenicity of their E2 glycoproteins. Systematic site-directed mutagenesis of the antigenic units has revealed residues that limit cross-reactivity. Our findings may be useful for the development of serological differential assays and improvement of immunogenicity of novel classical swine fever vaccines.

Identification of antigen-specific residues on E2 glycoprotein of classical swine fever virus

Envelope glycoprotein E2 of classical swine fever virus (CSFV) is the major antigen that induces neutralizing antibodies in infected pigs. Our previous study revealed that N-terminal 90 residues (domains B/C) of E2 play key roles in differentiating vaccine strain LPC/AHRI (subgroup 1.1) from the two field strains TD/96/TWN (subgroup 2.1) and 94.4/IL/94/TWN (subgroup 3.4) (Chang et al., 2010). This study further analyzed the reaction patterns between monoclonal antibodies (mAbs) and expressed hybrid N-terminal of E2 of the above-mentioned viruses, revealing that mAbs T33 and C2, mAbs V8 and T23, and mAbs L7 and L150 required binding sites specifically at residues 690-714 in domain B, residues 715-740 in domain C, and residues 741-765 in domain C, respectively. Site-directed mutagenesis further demonstrated that residues (713)E and (729)D were critical for antigenic specificity of field strain (94.4/IL/94/TWN), while residues (705)D and (761)K were specific for vaccine strain (LPC/AHRI). These specific residues likely mediated in determining the topography of mAb binding sites of E2 to allow for differentiation between strains based on the premise that the structural integrity of the conformational epitope is maintained.

An RNA-hydrolyzing recombinant antibody exhibits an antiviral activity against classical swine fever virus

Some proteins with ribonuclease (RNase) activity have been shown to suppress viral replication. A well-characterized recombinant antibody, 3D8 single-chain variable fragment (3D8 scFv), has RNA-hydrolyzing and cell-penetrating activities. Here, we investigated antiviral activity of 3D8 scFv against classical swine fever virus (CSFV). In a cell line expressing 3D8 scFv (C26), intracellular RNA-hydrolysis activity was higher compared to control PK-15 cells and viral replication was strongly suppressed at the viral RNA level, with the evidence of independency of IFN-alpha/beta induction. Exogenous treatment of 3D8 scFv, prior to or post-CSFV infection, was also shown to suppress CSFV replication at the viral RNA level. These observations suggest that antiviral activity of 3D8 scFv may be due to the intrinsic RNase activity of 3D8 scFv, which is capable of targeting viral RNA genomes or transcripts.

Genetic characterization of E2 gene of classical swine fever virus by restriction fragment length polymorphism and phylogenetic analysis

An RT-nested PCR (RT-nPCR)-based restriction fragment length polymorphism (RFLP) analyses of the E2 gene were developed for genetic subtyping and differentiation of vaccinated and infected classical swine fever virus (CSFV) strains. RT-nPCR identified 96 CSFV-positive samples from 321 clinical specimens from southeastern China during 2003-2008. The PCR products of positive samples were further differentiated using MspI digestion, 23 were identified as the C-strain, 62 as field strains, and 11 as mixture of the vaccine strain and field ones. RFLP with BglI, DdeI, DraI, and PstI were then used for subtyping of the field CSFV isolates. Thirty-eight field isolates phylogenetically classified as subgroup 2.1 based on E2 were divided into 11 subtypes by this RFLP scheme. Both RFLP profiling and sequence-based phylogenetic analysis revealed genetic diversity of CSFV in the field. Three novel substitutions at amino acid positions 17, 93, and 286 were identified in the predominant subtype VI strains isolated in 2008 as compared to other strains including historical subtype VI strains. These results suggest that CSFV in China experienced gradual variations and evolutionary accumulation progress. Thus, the RFLP methods targeting on the CSFV E2 gene are suitable for epidemiological survey in endemic area where the C-strain is applied for vaccination. Combination of the RFLP schemes with sequence-based phylogenetic analysis could provide more detailed information on transmission of CSFV in the region or even its evolution.

Evaluation of white spot syndrome virus variable DNA loci as molecular markers of virus spread at intermediate spatiotemporal scales

Variable genomic loci have been employed in a number of molecular epidemiology studies of white spot syndrome virus (WSSV), but it is unknown which loci are suitable molecular markers for determining WSSV spread on different spatiotemporal scales. Although previous work suggests that multiple introductions of WSSV occurred in central Vietnam, it is largely uncertain how WSSV was introduced and subsequently spread. Here, we evaluate five variable WSSV DNA loci as markers of virus spread on an intermediate (i.e. regional) scale, and develop a detailed and statistically supported model for the spread of WSSV. The genotypes of 17 WSSV isolates from along the coast of Vietnam--nine of which were newly characterized in this study--were analysed to obtain sufficient samples on an intermediate scale and to allow statistical analysis. Only the ORF23/24 variable region is an appropriate marker on this scale, as geographically proximate isolates show similar deletion sizes. The ORF14/15 variable region and variable-number tandem repeat (VNTR) loci are not useful as markers on this scale. ORF14/15 may be suitable for studying larger spatiotemporal scales, whereas VNTR loci are probably suitable for smaller scales. For ORF23/24, there is a clear pattern in the spatial distribution of WSSV: the smallest genomic deletions are found in central Vietnam, and larger deletions are found in the south and the north. WSSV genomic deletions tend to increase over time with virus spread in cultured shrimp, and our data are therefore congruent with the hypothesis that WSSV was introduced in central Vietnam and then radiated out.

Characterisation of experimental infections of domestic pigs with genotype 2.1 and 3.3 isolates of classical swine fever virus

The early identification of classical swine fever epizootics is hampered by difficulties in recognising early signs of infection, due to a lack of specific clinical signs. In addition many textbook descriptions of CSF are based on observations of disease caused by historic, mainly genotype 1, strains. Our objective was to improve our knowledge of the diverse range of signs that different CSFV strains can cause by characterising the experimental infection of domestic pigs with both a recent strain of CSFV and a divergent strain. Conventional pigs were inoculated with a genotype 2.1 isolate, that caused an outbreak in the UK in 2000, and a genotype 3.3 strain that is genetically divergent from European strains. This latter strain is also antigenically distinct as it is only poorly recognised by the CSFV-specific monoclonal antibody, WH303. Transmission was monitored by use of in-contact animals. Clinical, virological and haematological parameters were observed and an extended macro- and histopathological scoring system allowed detailed characterisation of pathological lesions. Infection with the genotype 2.1 isolate resulted in a similar outcome to other recent genotype 2 European strains, whereas the genotype 3.3 strain produced fewer and delayed clinical signs, notably with little fever. This strain would therefore be particularly difficult to detect in the early stages of infection and highlights the importance of encouraging early submission of samples for laboratory diagnosis. As representatives of recent and divergent CSFV isolates, these strains are good candidates to study the pathogenesis of current CSFV isolates and as challenge models for vaccine development.

Genetic typing of recent classical swine fever isolates from India

Seventeen classical swine fever virus (CSFV) isolates recovered during the period of 3 years (2006-2008) from India were subjected to nucleotide sequencing in the 5' untranslated region (UTR). For genetic typing, 150 nucleotides within this region were used. For better epizootiological understanding, 39 nucleotide sequences of the above region, including 13 Indian CSFV sequences, available either in the Genbank or published literature were also included in the study. Based on the phylogenetic analysis, the Indian isolates could be grouped in to two subgroups, viz., 1.1 and 2.2. The study also revealed predominance of subgroup 1.1 and involvement of viruses of more than one subgroup in an outbreak.

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.

A stochastic model to quantify the risk of introduction of classical swine fever virus through import of domestic and wild boars

Classical swine fever (CSF) is a disease of pigs that imposes major hardship on the industry of infected regions. The recent history of CSF epidemics suggests that animal movements remain the main source of CSF virus (CSFV) infection for susceptible populations in Europe. This study presents an assessment of the risk of introducing CSFV into Spain through the importation of live susceptible animals. Results suggest that, if prevailing conditions persist, introduction of CSFV into Spain is likely to occur on average every 9 years and that introduction is almost three times more likely to occur via domestic pigs than through wild boars. The highest risk was concentrated in March and in the Northeastern provinces of Spain. Results were consistent with the time and location of previous CSFV introductions into the country. The methodology and the results presented here will contribute to improve the CSF prevention programme in Spain.

Complete sequence of a subgroup 3.4 strain of classical swine fever virus from Taiwan

Classical swine fever viruses from Taiwan have been classified into two subgroups (3.4 and 2.1). Outbreaks caused by 3.4 viruses were reported in Taiwan prior to 1996 and which mainly distributed in the geographic range from southern Japan to Taiwan. We have determined the complete sequence of a reference strain, 94.4/IL/94/TWN. The genome contains 12,296 nucleotides, encoding 3,898 amino acids flanked by a 372-nt region at the 5' untranslated region (UTR) and a 227-nt region at the 3'-UTR. Similarities of nucleotides among 3.4 viruses isolated from Taiwan and Japan (Kanagawa/74; Okinawa/86) maintained in 94.2-97.5%; however, comparing to subgroup 1.1 (ALD/64/Jap) and 2.1 (TD/96/TWN) only showed about 72.5-80.8%, respectively. Phylogenetic analysis based on positioning from 11,157 to 11,565 nt (NS5B region) revealed that CSFVs were divided into three major lineages and their sublineages. Strain 94.4/IL/94/TWN is the first completely genomic sequence of subgroup 3.4 viruses.

Vaccination against classical swine fever virus: limitations and new strategies

The most widely used vaccines for the control of classical swine fever (CSF) in countries where it is endemic are live attenuated virus strains, which are highly efficacious, inducing virtually complete protection against challenge with pathogenic virus. In the European Union (EU), the combination of prophylactic mass vaccination and culling of infected pigs in endemic regions has made it possible to almost eradicate the disease. However, it is not possible to discriminate between infected and vaccinated animals, thus hampering disease control measures that rely on serology. Therefore, vaccination was banned at the end of 1990 before the internal common market was established in the EU. Vaccination is allowed only in severe emergencies. In addition, there are strict restrictions on the international trade in pig products from countries using vaccination. To circumvent these problems, marker vaccines which allow differentiation of infected from vaccinated animals (DIVA) have been developed. There are several approaches, ranging from protective peptides, single expressed proteins, naked DNA and chimeric viruses. To date, two subunit vaccines based on the E2 glycoprotein are commercially available and have been tested extensively for their efficacy. The accompanying discriminatory tests are based on an ELISA detecting another viral glycoprotein, the Erns. The subunit vaccines were found to be less efficacious than live attenuated vaccines. In addition, the currently available discriminatory tests do not provide high enough specificity and sensitivity. Although there is an urgent need for more advanced marker vaccines and better discriminatory tests, the development of new DIVA vaccines against CSF is hampered by the small market potential for these products.

A sequence database allowing automated genotyping of Classical swine fever virus isolates

Classical swine fever (CSF) is a highly contagious viral disease of pigs. According to the OIE classification of diseases it is classified as a notifiable (previously List A) disease, thus having the potential for causing severe socio-economic problems and affecting severely the international trade of pigs and pig products. Effective control measures are compulsory, and to expose weaknesses a reliable tracing of the spread of the virus is necessary. Genetic typing has proved to be the method of choice. However, genotyping involves the use of multiple software applications, which is laborious and complex. The implementation of a sequence database, which is accessible by the World Wide Web with the option to type automatically new CSF virus isolates once the sequence is available is described. The sequence to be typed is tested for correct orientation and, if necessary, adjusted to the right length. The alignment and the neighbor-joining phylogenetic analysis with a standard set of sequences can then be calculated. The results are displayed as a graph. As an example, the determination is shown of the genetic subgroup of the isolate obtained from the outbreaks registered in Russia, in 2005. After registration (Irene.greiser-wilke@tiho-hannover.de) the database including the module for genotyping are accessible under http://viro08.tiho-hannover.de/eg/eurl_virus_db.htm.