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.

Antibody Response in Cattle and Guinea Pigs Inoculated with Rabies Vaccines

One hundred ninety-five rabies cases in cattle were identified in South Korea since 1993. As most of rabies cases have a relation to rabid Korean raccoon dogs (Nyctereutes procyonoides koreensis), vaccination to animals including cattle is mandatory in rabies risk region. In order to minimize fatal rabies in animals, eradication policy of the disease has been achieved by controlling reservoirs and by mass vaccination. In this study, we compared the antibody response in cattle and guinea pigs inoculated with rabies vaccines commercially available in Korea. Each group of cattle in Gangwon-do was vaccinated intramuscularly with either one of five commercial inactivated vaccines or a live attenuated rabies vaccine (designated as A to F). Serum samples at the time of vaccination and four weeks post vaccination were obtained from the cattle and guinea pigs and were analyzed with virus neutralizing assay (VNA). Each group of cattle inoculating rabies vaccines showed significant virus neutralizing antibody titers (p < 0.05) ranging from 1.55 to 17.8 mean IU/ml compared with the non-vaccinated cattle and guinea pigs inoculated with 1/20 dose of vaccine showed relatively low VN antibody titers ranging from 0.23 to 6.1 mean IU/ml. All cattle immunized with A, C and F showed high VN antibody titers over 0.5 IU/ml and 62.5% and 37.5% of cattle inoculated with D and E showed protective antibody titer, respectively. This finding suggests that the inactivated or live attenuated rabies vaccination commercially available in Korea could induce protective antibody response in Korean cattle, but sero-conversion rate and sero-positive rate showing VN antibody titer over 0.5 IU/ml depend on vaccines.

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.