- 學位論文
探討豬第二型環狀病毒中和抗體及病毒量於現場豬隻之相關性
Correlation between the Neutralizing Antibodies against Porcine Circovirus Type 2 (PCV2) and the Viral Load in Conventional Pig Herds
摘要
豬第二型環狀病毒 (porcine circovirus type 2；PCV2) 為造成豬隻離乳後多系統消耗性症候群 (postweaning multisystemic wasting syndrome ; PMWS) 之重要病原。近年研究顯示，感染PCV2的患豬淋巴組織會受到破壞，且同時影響細胞性免疫及體液性免疫系統表現。依據血清學調查結果，現場豬隻抗體陽性率接近100%，而抗體的產生及消長，除了反應免疫系統受到病毒刺激外，也可能控制著PCV2的複製並影響PMWS之疾病進展；特別是中和抗體 (neutralizing antibody；NA) 的表現，可能為左右PCV2病毒量之重要因素。於人工感染PCV2的實驗中發現，豬隻病毒血症的減緩，往往只在中和抗體血清陽轉之後發生；故學者認為中和抗體的缺乏和病毒複製的增加，兩者間緊密相關。然而，單純探討中和抗體和PCV2病毒量於現場豬隻的表現，卻不具統計上之負相關意義，中和抗體也無法將血清中PCV2病毒完全清除。因此，本實驗的目的為，藉由將豬隻飼養於一乾淨環境中，先單純探討中和抗體和PCV2病毒量變化之相關性；再於現場不同症狀的豬隻中，探討兩者關係之變遷，並期望能進一步了解體液性免疫和PCV2病毒量之相關性。實驗以兩階段進行；第一階段，選取6頭健康PCV2帶原豬隻，由5週齡開始持續採血至16週齡；第二階段，由雲林及屏東5個具有PMWS病史豬場，選取6-9週齡保育豬，共61頭，依據其臨床症狀分為三組 (healthy、mild與severe group)；偵測兩階段所有豬隻PCV2抗體、中和抗體力價以及PCV2病毒量表現，進行中和抗體與PCV2病毒量相關性分析。實驗結果顯示，飼養於乾淨環境豬隻，其NA的發展，能與總PCV2抗體 (total PCV2 antibody；TA) 一致地變化，而有效降低PCV2病毒量，並達到完全清除病毒血症。於現場豬隻方面，可見PCV2普遍存在於6至9週齡保育豬，雖然豬隻有不等程度之臨床症狀，但皆可產生不同高低力價之PCV2抗體以及中和抗體。然而，NA和PCV2病毒量兩者之負相關僅存在於severe group豬隻。
並列摘要
The phenomenon of impaired humoral immunity against PCV2 has been commonly noticed in postweaning multisystemic wasting syndrome (PMWS)-affected pigs. In previous research, PCV2 neutralizing antibody (NA) titer was inversely correlated with PCV2 load in experimentally inoculated pigs. However, the same correlation failed to be demonstrated in naturally PMWS-affected pigs. The aim of current study was to further investigate the humoral response against PCV2 via evaluating development and production of NA in pigs with different ages and clinical status. In first part of the study, 6 healthy field PCV2-carrier pigs were kept in laboratory animal house and studied in duration of 5 to 16 weeks of age. In second part of the study, 61 nursery pigs in 6-9 weeks of age from 5 different farms were categorized into three groups, namely healthy, mild, and severe animals based on clinical status. The determination of NA, total PCV2 antibodies (TA), and PCV2 load were comparatively studied as well as correlated with clinical status in all studied pigs. The results showed the presence of NA was able to diminish PCV2 load and completely eliminate viremia in 6 healthy field PCV2-carrier pigs. In field pigs, the highest NA and TA titer, and the lowest PCV2 load was present in the severe group. Additionally, the inverse correlation between PCV2 load and NA or TA titers only existed in pigs of severe group. In conclusion, the presence and development of NA can effectively diminish the PCV2 load with the synergistic aid of TA in some circumstances.