|摘要: ||豬離乳後多系統性消耗性症候群(postweaning multisystemic wasting syndrome, PMWS)亦稱豬環狀病毒相關疾病(porcine circovirus associated disease, PCVAD)，為近年來一重要新興豬病，其發生與PCV2 (porcine circovirus type 2)感染有關，又常與其他病原如PRRSV (porcine reproductive and respiratory syndrome virus)混合感染導致更嚴重之病情。有關PCVAD之防治除落實高度衛生管理外，疫苗的使用被認為是有效策略，而甘蔗萃取物(sugar cane extract, SCE)為一種天然產物，具有免疫調節功能，有研究顯示可降低PRRSV抗體轉陽率及病毒核酸之陽性檢出率，認為具降低PRRSV之感染及散佈。本試驗主要目的在評估以改良後大腸桿菌表現之PCV2/ORF2所製作之次單位疫苗之保護效益。試驗一豬隻以3週離乳隔離飼養，以降低PRRSV自然感染方式及以人工感染PCV2來探討疫苗保護效益，並同步觀察移行抗體高低程度對PCV2感染之影響。試驗豬隻於3及6週齡時進行免疫，並於9週齡時進行PCV2病毒接種，以臨床病徵、生長性能、病理變化、血清抗體及PCV2病毒量表現等來評估疫苗保護效益。結果所有試驗豬並無明顯PRRSV感染，在PCV2接種後試驗豬隻無明顯臨床病徵，呼吸道相關病變也極為輕微。免疫組在PCV2接種後第2及第3週平均發燒天數(0.33及0天)略低於未免疫組(0.5及1.67天)；日增重(0.58±0.10 kg/day)則略高於無免疫組(0.51±0.10 kg/day)。淋巴組織病毒量方面，免疫組與無免疫組間並無顯著性差異，但遠高於5週齡有較高移行抗體之感染組。顯示疫苗免疫僅呈輕度保護作用及效益，此外，較高之移行抗體對豬群具有較高之保護作用。試驗二則選取4週齡離乳，但未隔離飼養之商業用豬並讓豬群自然曝露於PRRSV感染，並以相同模式再次評估疫苗保護效益外，另設2組分別於攻毒前或攻毒時給予免疫調節物質SCE，以觀察SCE對PRRSV或PCV2感染之影響。結果大部分豬隻於試驗前或試驗期間已有PRRSV感染現象(血清100%轉陽)，在 PCV2接種後，亦可誘發相當程度之呼吸道病變，並導致部份免疫豬隻發病死亡，無法呈現疫苗保護作用及效益。然而給予SCE的豬隻其臨床表現及病變均較陽性對照組為輕微，淋巴組織及血漿的病毒量也較為低，推測SCE可提升豬隻免疫力進而降低PCV2之感染。以上結果顯示，在PCV2與PRRSV共同感染時，的確可誘發相當程度之臨床症狀與呼吸道病變，而疫苗之保護效益則尚待進一步試驗與評估。以上研究顯示，PCVAD的防治上首在落實良好衛生管理，亦可考慮免疫母豬提高移行抗體力價以提供較多的保護作用，或於適當時期餵飼SCE以提升豬隻先天性免疫來控制PCVAD。|
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 (0.580.10 kg/day) than in non-vaccination group (0.510.10 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.