Clin Exp Vaccine Res.  2018 Jan;7(1):61-69. 10.7774/cevr.2018.7.1.61.

Efficacy of inactivated variant porcine epidemic diarrhea virus vaccines in growing pigs

• Lee SH
• Yang DK
• Kim HH
• Cho IS

• KMID: 2402539
• DOI: http://doi.org/10.7774/cevr.2018.7.1.61

Abstract

PURPOSE
The first aim of this study was to develop a novel inactivated porcine epidemic diarrhea virus (PEDV) vaccine using the recently isolated Korean PEDV QIAP1401 strain and to evaluate its protective efficacy in growing pigs. The second was to determine the optimum adjuvant formulation of the inactivated PEDV vaccine that induces protection against viral challenge.
MATERIALS AND METHODS
To generate high titers of infectious PEDV, the QIAP1401 isolate was passaged in Vero cells. The experimental vaccines were prepared from a binary ethyleneimine-inactivated QIAP1401 strain passaged sequentially 70 times (QIAP1401-p70), formulated with four commercial adjuvants, and administered twice intramuscularly to growing pigs. Challenge studies using a virulent homologous strain of PEDV QIAP1401-p11, which was passaged 11 times after isolation, were performed to assess protection against disease progression and viral shedding during the 15-day observation period. The vaccine-induced antibody responses were measured in serum samples collected at predetermined time points by indirect enzyme-linked immunosorbent assay and virus neutralization test.
RESULTS
The QIAP1401-p70 strain had 42 amino acid (aa) mutations, including a 25 aa deletion, and was selected as the inactivated PEDV vaccine candidate. Although none of the pigs that received the experimental vaccines were completely protected against subsequent viral challenge, they exhibited a significantly higher immune response than did non-vaccinated control pigs. Among the vaccine groups, the highest antibody responses were observed in the pigs that received an oil-based multiphasic water/oil/water (W/O/W) emulsion adjuvanted vaccine, which delayed the onset of clinical symptoms and viral shedding.
CONCLUSION
A novel inactivated PEDV vaccine formulated with a W/O/W emulsion adjuvant was both immunogenic and protective against viral challenge.

Keyword

Porcine epidemic diarrhea virus; Vaccines; Adjuvant; Growing pigs

MeSH Terms

Antibody Formation
Disease Progression
Enzyme-Linked Immunosorbent Assay
Neutralization Tests
Porcine epidemic diarrhea virus*
Swine*
Vaccines*
Vero Cells
Virus Shedding
Vaccines

Figure

• 

  Fig. 1 (A) Genetic characterization of QIAP1401-p70. A cell-culture-adapted QIAP1401 variant was generated by passaging 70 times using the sequential limit dilution culture method. The whole genome sequence of QIAP1401-p70 was determined by next-generation sequencing technology and compared with the reference sequences of genogroup G2: USA/Iowa303/2014 (KR265827), USA/Minnesota250/2014 (KR265776), and OH1414 (KJ408801). QIAP1401-p70 had 42 aa variations, of which a 25 aa deletion in ORF1a was notable. (B) QIAP1401-p70 emerged after 41 sequential passages.

• 

  Fig. 2 Clinical score and viral shedding in pigs after challenge with virulent homologous virus (porcine epidemic diarrhea virus [PEDV] QIAP1401-p11). Diarrhea severity was scored (A), and viral shedding in feces was monitored by real-time reverse transcription polymerase chain reaction (B). The letter “a” above the bars indicates a significant difference among the experimental groups (p<0.05, Fisher exact test), whereas “b” indicates no significant difference. NVC, non-vaccinated control.

• 

  Fig. 3 Serum immune response of pigs in the IMS1313, IMSgel, ISA201, and ISA206 groups. Pigs were vaccinated at 2-week intervals and then challenged with virulent homologous virus (porcine epidemic diarrhea virus [PEDV] OIAP1401-p11). Serum samples collected at 0, 14, 28, and 48 days post-vaccination (dpv) (15 days post-challenge [dpc]) were subjected to enzyme-linked immunosorbent assay (ELISA) (A and B) and virus neutralization (VN) test (C and D) of PEDV-specific IgG and virus-neutralizing antibody titers, respectively. Bars represents the means standard deviation of five independent samples. *, **, and *** indicate significant differences from the non-vaccinated control (NVC) group (p<0.05, p<0.01, and p<0.001, respectively, unpaired Student's t test). Different lower-case letters above the bars indicate significant differences among the groups (p<0.05, Tukey's post hoc test).

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