E. coli表現之PCV2 ORF2次單位疫苗之效益評估及PRRS病毒在協同引發PCV2相關疾病之角色

Abstract

Postweaning multisystemic wasting syndrome (PMWS), also named as porcine circovirus associated disease (PCVAD), is an important emerging disease in swine in recent years. Porcine circovirus type 2 (PCV2) has been demonstrated to be the cause associated with PMWS. PCV2 co-infection with other pathogen, i.e. porcine reproductive and respiratory syndrome virus (PRRSV), is common and exacerbates the severity of PMWS. In addition to the implement of high level of biosecurity of farms, the use of the PCV2 vaccine is an effective strategy to control PCVAD. Sugar cane extract (SCE) is a native immunomodulator and can reduce the severity of infection. The objective of the present study was to evaluate the efficacy of the novel E. coli expressed PCV2/ORF2 subunit vaccines. The first experiment we evaluated the efficacy of PCV2 vaccines on conventional pigs under experimental control with less PRRSV exposure and the effects of PCV2 maternal antibodies on pigs experimentally infected with PCV2. Experimental pigs received double vaccinations of PCV2 subunit vaccine at 3 and 6 weeks of age, and then were inoculated with PCV2 inocula at 9 weeks of age. The clinical symptoms, pathological lesions, PCV2 loading and PCV2 antibody profile were evaluated. The results displayed that all experimental pigs after PCV2 inoculation presented mild clinical signs and respiratory lesions. Mean days of fever during 4 weeks inoculation after PCV2 challenge were slightly lower in vaccination group than in non-vaccination group. In contrast, mean daily weight gain were slightly higher in vaccination group (0.58±0.10 kg/day) than in non-vaccination group (0.51±0.10 kg/day). However, there was no significant difference in PCV2 loading between vaccination and non-vaccination group, but was significantly higher than PCV2 inoculated group at 5 weeks of age. Experiments above shows mild efficacy of the novel PCV2 subunit vaccine on these vaccinated pigs and high maternal antibodies offer more protection for piglets. The second experiment the evaluation of the efficacy of vaccines was repeated, that experimental pigs were naturally exposure to PRRSV infection. Moreover, effects of SCE on PRRSV or PCV2 infection were also included. The results displayed that most pigs suffered from PRRSV and PCV2 co-infection with more severe clinical signs and pulmonary lesions. The efficacy of the PCV2 vaccine on vaccinated pigs was not supported under PRRSV and PCV2 co-infection. However, pigs fed with SCE presented milder clinical signs, lesions, and PCV2 load in tissues. Therefore, SCE administration might have an immunostimulating effects on porcine immunity to reduce the pulmonary impairment against PCV2 and PRRSV co-infection. Taken together, co-infections with PCV2 and PRRSV can induce severe pulmonary lesions and clinical signs. The efficacy of the novel PCV2 subunit vaccine remains further elucidation. With the implement of high level of hygiene, increasing maternal antibody to confer more protection to piglets by means of boosting sows with PCV2 antigen, and feeding SCE in appropriate time, could be considered as another strategy in the control of PCVAD.