Enhancing Specific Antibodies Using a Developed Sub-unit PCV2b Vaccination in a PCV2-affacted Herd

Abstract

Porcine circovirus type 2 (PCV2) causes multisystemic diseases called porcine circovirus associated disease (PCVAD) in pigs leading to a significant economic loss in the swine industry. The objective of this study was to determine the efficacy of a developed sub-unit PCV2b vaccine using a recombinant truncated capsid protein expressed in Escherichia coli in PCVAD-affected pig farms. Five-week-old conventional pigs were allocated into 2 groups: vaccinated (n = 55) and control (n = 55) groups placed in the same building. The vaccinated pigs were given two shots of a developed vaccine with 2-week interval on day 0 and 14. Serum samples were collected from 10 randomly selected pigs of each group. IPMA and in-house indirect ELISA were used to evaluate antibody titers on 0, 14, 28, 77 and 119 days post first vaccination (dpv). Viral load of PCV2 in serum was determined by a modified real-time PCR on 0, 14, 28, 77 and 119 dpv. The IPMA results revealed that the vaccinated pigs had significantly higher antibody titers than the control pigs (4.90±0.99 log2, 2.50±0.85 log2, respectively) at 28 dpv (p < 0.05). While the ELISA test showed significantly higher differences (p < 0.05) of means S/P ratios between the two groups at 28 dpv (0.688±0.270 and 0.200±0.17) and at 119 dpv (1.440±0.38 and 0.808±0.47). The PCV2 viral loads in the vaccinated pigs were significantly lower than those of the control pigs at 28 dpv (4.97±0.25, 5.20±0.10), 77 dpv (4.71±0.38, 6.03±1.41) and 119 dpv (4.26±0.25, 5.03±0.67). Even though the vaccinated pigs showed lower viral loads than the control pigs, their viral loads were rather high from 28 dpv onward possibly due to natural PCV2 infection. The results indicated that vaccination by developed sub-unit PCV2b vaccine could induce humoral antibody and partially control PCV2 viral load in serum which resulted in higher protein concentration dose and/or using an appropriate adjuvant could enhance better efficacy of this developed sub-unit vaccine. This study demonstrated that the developed sub-unit PCV2b vaccine had potential for use as a future vaccine candidate. However, more field trials on production parameter and other parameters are needed for vaccine efficacy evaluation.