Study on trial vaccine using porcine epidemic diarrhea virus recently isolated in Korea

Porcine epidemic diarrhea caused by PEDV infection inflicts severe damages to swine industry. Though several attenuated strains such as CV777 and SM98 were used to vaccine production, recently field isolated strains were different from vaccine strains genetically as well as serologically. Recent PEDV isolates in Asia and USA show more contagious and more severe mortality than previous PEDV. Continuous vaccine strain development is essential for effective PEDV prevention and control. Therefore new field strain isolation and cultivation in the laboratory is first step for effective vaccine development against new variant. This study shows pathogenicity and immunogenicity of PED-CUP-B2014 strain currently isolated in Korea.

Clinical samples for PEDV isolation are prepared from feces and intestinal homogenates of piglets that was show typical PEDV infected symptoms. Spike protein specific real-time RT-PCR was tested for identification of PEDV positive sample. RT-PCR positive samples were mixed with sterilized PBS and centrifuged at 4,200g for 10 minutes at 4°C. The supernatants were filtered through a 0.22-μm filter and used as inoculums for virus isolation. Virus isolation and culture was performed in Vero cell line. Phylogenetic analysis was performed using the nucleotide sequences of spike protein of the six PEDV viruses from this study as well as other PEDV strains. Lab scale trial vaccine was prepared by several different concentration of PED virus and used with same adjuvant and some additive. Post vaccination pig serum neutralization antibody titer was measured by standard method.

Virus isolation was attempted with PEDV-PCR positive feces and PEDV-PCR positive intestine homogenates was inoculated on Vero cells. The inoculated Vero cell was showed typical PEDV CPE such as cell fusion and syncytium formation. The cell observed CPE was cultured continuously in order to isolate PEDV. PEDV isolate was efficiently propagated and maintained in Vero cell cultures. After more than 60 continuous passages, isolated PEDV titer was reach to 10^8.0TCID₅₀/ml. The nucleotide sequence of spike of the PEDV isolate was different from that of previous isolated PEDV. SN titer of each vaccine group was depending on concentration. Highest SN titer was 160 in the group vaccinated with 10 ^7.0 TCID₅₀.

In this study, new variant PEDV in Korea was isolated and also successfully cultured on the Vero cell. Phylogenetic analyses show new PEDCUP-B2014 completely different from previous PEDV. Trial Vaccine of the PED-CUP-B2014 raised enough SN antibody titer to prevent PEDV infection and diarrhea.

Disclosure of Interest: None Declared.