台灣地區山羊關節炎腦炎之血清學監控,預防和控制

Abstract

中 文 摘 要 山羊關節炎腦炎(Caprine arthritis encephalitis ;CAE)為慢性消 耗性疾病，並廣泛流行於世界各地，可引起 極大的經濟損失，台灣地 區已成為高流行地區。本試驗進行 CAE血清學監控，病毒傳染途徑的探 討及建立ELISA篩檢法， 以期建立控制本病之方法及建立CAE陰性羊群之 目的。 從77年4月至85年12月間，由台灣北、中、南部地區9 縣市27乳羊場所採得之1170件成年乳羊血清樣品，以ELISA 法進行CAE 血清抗體檢測結果顯示：所有羊場均為陽性場， 77年至85年間CAE血清 抗體陽性件數有691件(59.1%）。經臨 床檢查關節腫大病羊與血清抗體 檢測為陽性間之關係，結果 顯示有顯著的相關性（P<0.01)。對8縣市23 場乳羊戶進行問 卷調查，結果顯示成年乳羊在一年內，平均有12.3%羊 隻形 成關節腫大病症，而其中58.6%的關節腫大羊隻在2歲時被畜 主 提早2年淘汰；配合CAE陽性羊每日每隻減產0.34公升乳 量，可以估算 CAE對乳羊場，每年平均可造成總收入13.7% 的經濟損失。 在傳播途徑方面，集乳(pooled milk)方式為本病最主 要傳播方式。水 平感染可成立，陰性母羊群與陽性母羊群同 居一年內，有33.3%的血清 轉陽率；並無明顯證據顯示可經 由交配或胎盤等途徑傳播本病。乳汁 中病毒經56℃1小時加 熱，可使病毒不活化，失去感染能力。因此可藉 由乳汁加熱 來消滅感染源。 以濃縮病毒液(CAEV-TC1株）作為ELISA抗原，經由棋盤 式測定，最適抗 原濃度是4mg/ml。以此ELISA檢測血清、乳 汁及關節液中之抗體，以及 檢測194件野外血清樣品，並與 西方墨點法作比較試驗，二方法之相對 敏感性為99%，相對 特異性為91.3%，相對一致性為95.4%，Kappa 值 為0.9，顯 示兩者有極高相符性。 在建立陰性羊群方面，仔羊食用56℃1小時以上加熱處 理之初乳並與陽 性成羊在不同棟羊舍隔離飼養，仔羊於6至 11月齡時，CAE平均轉陽率 為15.2%；若初乳加熱處理並與陽 性成羊在同棟羊舍，只隔欄飼養，仔 羊於6至11月齡時，CAE 平均轉陽率為24.5%；仔羊食用未加熱處理之初 乳與陽性成 羊在同棟羊舍，只隔欄飼養，仔羊於6至8月齡時，CAE平均 轉陽率高達81.3%。顯示加熱處理及隔離飼養對控制本病之 感染有顯著 之效果。 由以上結果顯示， 台灣地區已經是CAE高污染地區，且 對乳羊場有極高的潛在性經濟損失 。將初乳集乳後餵養同批 仔羊是本病主要之傳播途徑，其次為同居感染 。在CAE的監 控與淨化措施，ELISA是敏感且快速的檢測法。將初乳加 熱 處理及仔羊適當隔離飼養，可明顯降低仔羊的感染率。

Summary Caprine arthritis encephalitis (CAE) is one kind of chronic wasting disease which causes great financial losses in dairy goat industry. The disease has been spread worldwidely including Taiwan. In this research we worked on the serological surveillance, blockade of transmission route, and establishment of ELISA test and tried to construct a model for CAE free goat farm. From 1988 to 1996, we collected 1170 serum samples from 27 goat farms for CAE serological study using ELISA method. The results indicated that all of the farms were contaminated with CAE virus and the positive samples were 691 (59.1%). Through the observation of swollen joints of goats in the field compared to CAE antibody, there was a remarkable correlation between both factors (p<0.01). We further questionnaired 23 dairy goat farms for the economic loss caused by swollen joints. Those results revealed that there was 12.3% of goats showing swollen joints within one year, and 58.6% of those goats at the age of 2 culled by raiser. Matching study of the milking performance and CAE virus infection in one dairy goat farm showed CAE virus infected goats decreasing 0.34 liter milk production per goat per day compared to uninfected goats, which was equal to 13.7% economic loss of net income. Pooled milking was the major transmission route in CAE transmission of goat kids, but the horizontal route was also important in young and adult goats when they were raised in poor environmental condition. The CAE seronegative goats living with CAE seropositive goats for one year showed 33.3% seroconversion rate. No obvious evidence proved the transmission of the disease was through mating and transplacental route. In vitro study indicated that the infectivity of the virus in milk was lost after heated the milk to 56℃for an hour. In this study we aslo established ELISA method for CAE antibody detection. After box titration, the proper virus protein concentration was 4mg/ml. Compared ELISA method with Western blotting, there was a relative high correlation between them. From the comparison of 194 serum samples, the relative sensitivity was 99%, the relative specificity was 91.3% and the correlation of both methods was 95.4%. According to above results, we followed the serological surveillance on dairy goat farms which heated pooled colostrum to feed kids and separate kids from their dams after born. The average seroconversion rates of goats, which were separated from their dams in different house and pens at the age of to 11 months, were 15.2% and 24.5%, respectively. In contrast goat kids fed with unheated colostrum and only separated from their dams in different pens showed 81.3% positive for CAEV infection at the age of 8 months. The above results indicated that Taiwan has become a high prevalent area of CAE virus infection which potentially causes a large amount of financial losses. It is the main transmission route of the disease to feed untreated pooled milk for kids, and living together second. ELISA is a sensitive and rapid monitor method for CAE virus infection. Heated colostrum and separated CAE seronegative goats from positive goats can efficiently reduce the infection.