Safety and Immunogenicity of Chimeric Pestivirus KD26_E2LOM in Piglets and Calves.

A chimeric pestivirus (KD26_E2LOM) was prepared by inserting the E2 gene of the classical swine fever virus (CSFV) LOM strain into the backbone of the bovine viral diarrhea virus (BVDV) KD26 strain. KD26_E2LOM was obtained by transfecting the cDNA pACKD26_E2LOM into PK-15 cells. KD26_E2LOM chimeric pestivirus proliferated to titers of 106.5 TCID50/mL and 108.0 TCID50/mL at 96 h post-inoculation into PK-15 cells or MDBK cells, respectively. It also reacted with antibodies specific for CSFV E2 and BVDV Erns, but not with an anti-BVDV E2 antibody. Piglets (55-60 days old) inoculated with a high dose (107.0 TCID50/mL) of KD26_E2LOM produced high levels of CSFV E2 antibodies. In addition, no co-habiting pigs were infected with KD26_E2LOM; however, some inoculated pigs excreted the virus, and the virus was detected in some organs. When pregnant sows were inoculated during the first trimester (55-60 days) with a high dose (107.0 TCID50/mL) of KD26_E2LOM, anti-CSFV E2 antibodies were produced at high levels; chimeric pestivirus was detected in one fetus and in the ileum of one sow. When 5-day-old calves that did not consume colostrum received a high dose (107.0 TCID50/mL) of KD26_E2LOM, one calf secreted the virus in both feces and nasal fluid on Day 2. A high dose of KD26_E2LOM does not induce specific clinical signs in most animals, does not spread from animal to animal, and generates CSFV E2 antibodies with DVIA functions. Therefore, chimeric pestivirus KD26_E2LOM is a potential CSFV live marker vaccine.

Antigenic characterization of classical swine fever virus YC11WB isolates from wild boar.

Classical swine fever (CSF), a highly contagious disease that affects domestic pigs and wild boar, has serious economic implications. The present study examined the virulence and transmission of CSF virus strain YC11WB (isolated from a wild boar in 2011) in breeding wild boar. Virulence of strain YC11WB in domestic pigs was also examined. Based on the severe clinical signs and high mortality observed among breeding wild boar, the pathogenicity of strain YC11WB resembled that of typical acute CSF. Surprisingly, in contrast to strain SW03 (isolated from breeding pigs in 2003), strain YC11WB showed both acute and strong virulence in breeding pigs. None of three specific monoclonal antibodies (7F2, 7F83, and 6F65) raised against the B/C domain of the SW03 E2 protein bound to the B/C domain of strain YC11WB due to amino acid mutations (720K→R and 723N→S) in the YC11WB E2 protein. Although strains YC11WB and SW03 belong to subgroup 2.1b, they had different mortality rates in breeding pigs. Thus, if breeding pigs have not developed protective immunity against CSF virus, they may be susceptible to strain YC11WB transmitted by wild boar, resulting in severe economic losses for the pig industry.

Surveillance of classical swine fever in wild boar in South Korea from 2010-2014.

Classical swine fever (CSF) is a highly contagious systemic hemorrhagic viral disease of pigs. Wild boar plays a crucial role in the epidemiology of CSF. Between 2010 and 2014, samples were collected nationwide from 6,654 wild boars hunted in South Korea. Anti-CSF antibodies were identified in 0.59% (39 of 6,654) of the wild boar samples using a virus neutralization test and were primarily detected in wild boars living close to the demilitarized zone and the area of the Taebaek Mountains surroundings. The CSF virus (subgroup 2.1b) was isolated from two wild boars captured in a nearby border area. The criteria used to define high-risk areas for targeted CSF surveillance in South Korea should be further expanded to include other regions nationwide.

Serological prevalence of viral agents that induce reproductive failure in South Korean wild boar.

BACKGROUND: Viral agents associated with reproductive failure such as Aujeszky's disease virus (ADV), encephalomyocarditis virus (EMCV), and porcine parvovirus (PPV) have also been identified in European wild boar. To screen for the presence of antibodies against ADV, EMCV, and PPV from wild boar (Sus scrofa) in South Korea, 481 serum samples were collected from wild boar hunted between December 2010 and May 2011. RESULTS: Of the 481 serum samples tested, 47 (9.8%) and 37 (7.7%) were seropositive for ADV and EMCV antibodies, respectively, based on a neutralization test (VNT), and 142 (29.5%) were seropositive for PPV antibodies based on a hemagglutination inhibition (HI) test. CONCLUSIONS: This was the first survey to identify the seroprevalence of the three major viruses associated with reproductive failure in the wild boar population of South Korea. Wild boar may act as a reservoir for many viruses that cause infectious diseases in domestic pigs. Thus, strict prevention and control measures, such as continuous wildlife disease surveillance and strategic methods of downsizing the population density, should be implemented to prevent disease transmission from wild boar to domestic pigs.

Complete genome sequences of classical Swine Fever virus strains isolated from wild boars in South Korea.

Classical swine fever is a disease that is devastating the pig industry worldwide. Here, we report the complete genome sequences of two classical swine virus strains (YC11WB and PC11WB), isolated from Korean wild boars in 2011. Both strains belong to subgenotype 2.1b. The complete genome sequences of PC11WB and YC11WB are more similar to that of strain ZJ0801 (isolated in China) than to that of the SW03 strain isolated from domestic pigs in South Korea.

Significance of genetic variation of PRRSV ORF5 in virus neutralization and molecular determinants corresponding to cross neutralization among PRRS viruses.

A high rate of genetic and antigenic variability among porcine reproductive and respiratory syndrome viruses (PRRSVs) hampers effective prevention and control of the disease caused by PRRSV. The major envelope protein (GP5) encoded by the ORF5 of PRRSV has a critical role in inducing virus neutralizing (VN) antibody and cross protection among different strains of PRRSV. This study was conducted to identify sequence elements related to cross neutralization by comparing the ORF5 sequences of 69 field isolates in conjunction with their susceptibility to VN antibody raised against the VR2332 strain in vitro and in vivo. Five common variable sites (amino acid position 32-34, 38-39, 57-59, 137 and 151) were identified between susceptible and resistant viral isolates. Mutants whose ORF5 amino acid sequences were substituted with the sequences corresponding to the 5 identified common variable sites individually or concurrently were generated from a VR2332-backboned infectious clone by site mutagenesis. The change in the susceptibility of the mutants to VN antibodies specific for VR2332 or a heterologous PRRSV was assessed to determine the association of those 5 identified sites with cross neutralization. Among the five sites, the changes of amino acid sequences at three sites (32-34, 38-39, and 57-59) located in the N-terminal ectodomain of ORF5 significantly influenced the susceptibility of the mutant viruses to VN antibody, suggesting that sequence homology at these sites can be utilized as genetic markers to predict the degree of cross neutralization among different PRRSVs.

A survey of porcine reproductive and respiratory syndrome among wild boar populations in Korea.

No information is currently available on porcine reproductive and respiratory syndrome virus (PRRSV) infection in wild boars (Sus scrofa) in Korea. In this study, the status of PRRS in wild boars was investigated. Blood samples were collected from 267 wild boars from eight provinces in Korea. Four of the samples tested (1.5%) were positive for PRRSV antibodies and eight (3.0%) were positive for antigens. Of the virus-positive samples, three and five samples were typed as containing European (EU, type 1) or North American (NA, type 2) viruses, respectively. Two amplicons (one from type 1 and one from type 2) were used to analyze the PRRSV open reading frame 7 (ORF7) sequence. The nucleotide sequences of type 1 PRRSV ORF7 had identities between 96.1% and 98.4% with PRRSVs from domestic pigs in Korea. The sequences of type 2 PRRSV ORF7 had identities of 100% with the PRRSV strain VR-2332, which was prototypic North American strain. These results show that PRRSVs are present in wild boars in Korea, and effective PRRSV surveillance of the wild boar population might therefore be useful for disease control.

Different biological characteristics of wild-type porcine reproductive and respiratory syndrome viruses and vaccine viruses and identification of the corresponding genetic determinants.

Two attenuated vaccines, Ingelvac PRRS MLV and Ingelvac PRRS ATP, derived from VR2332 and JA142, respectively, have been used to control porcine reproductive and respiratory syndrome (PRRS) virus. However, there have been several field reports concerning the reversion of the vaccine virus to virulence. Furthermore, viruses genetically indistinguishable from the vaccines and wild-type parental viruses have been detected in clinical PRRS cases, raising the need for a better differential tool. As the vaccine viruses replicated better and produced bigger plaques in MARC-145 cells than did the wild-type parental strains, the following study was conducted to determine if the growth difference in MARC-145 cells can be utilized to differentiate a vaccine-like virus (VLV) from a wild-type virus and to identify genetic markers corresponding to such phenotype of the vaccine viruses. The relatedness of 83 field isolates collected between 1996 and 2005 to VR2332 and JA142 was classified genetically and antigenically. Thirteen of 25 VR2332-related viruses and 9 of 10 JA142-related viruses were determined as VLVs, since those viruses produced plaques similar to those by the vaccine viruses. Four unique amino acids each were identified throughout structural genes for MLV and ATP. Among those, F(10) in open reading frame 2 (ORF2) of MLV and E(85) and Y(165) in ORF3 of ATP were stable during pig passages. When the sequences unique for MLV were incorporated into an infectious clone constructed based on VR2332, the virus growth and resultant plaque size in MARC-145 cells were increased, suggesting that these sequences can be used as genetic markers for VLVs.