臺灣牛海綿狀腦病量化風險評估

Abstract

本研究針對臺灣自牛海綿狀腦病（bovine spongiform encephalopathy, BSE）疫區國進口活牛及肉骨粉數量，評估臺灣養牛產業環境至少發生一起病例之機率，依據病原特性與國內牛隻養殖、屠宰、化製處理、飼料場作業情形，建構BSE風險評估樹狀圖，收集風險因子資料及推估風險數值。風險評估樹狀圖中共包含五項程序及四項風險路徑，運用@RISK軟體，將風險路徑以Latin Hypercube抽樣方法重複測定10,000次，依此估算最終風險數值。結果顯示，臺灣於1979年至2004年自疫區國進口牛隻及肉骨粉，造成臺灣地區至少發生一起BSE病例之最大風險為4.84E-4，評估結果其風險不可忽略，另依英國發生率遞減情形估算，2004年該風險值已降至百萬分之一以下，目前已達可接受範圍。牛隻主要由美國、加拿大及日本進口，其殘體製成肉骨粉餵飼牛隻之總風險值為5.08E-12，另為估算自疫區進口牛隻造成垂直傳播病例之風險，本研究模擬試算結果風險值為7.79E-14~1.09E-8。由敏感性分析可知，遭病原污染之肉骨粉作為牛隻飼料之機率與本研究推估之最終風險值相關性最大，因此，持續注意國際疫情，堅持反芻獸餵飼動物性飼料禁令，為重要疾病風險管制點。

The study evaluated the probability of bovine spongiform encephalopathy (BSE) invasion into cattle breeding circumstances in Taiwan by importing cattle and meat and bone meal (MBM) from infected country. According to pathogen characteristic, cattle farming, slaughter, rendering and feeding circumstances, the BSE risk assessment scenario tree was constructed, information of risk factors were collected and risk values were evaluated. The BSE risk assessment scenario tree included 5 sections and 4 pathways. The final risk value was simulated with 10,000 times of Latin Hypercube simulations by @RISK software. The results revealed the maximum risk of producing at least one case of BSE in Taiwan was 4.84E-4 depending on importing cattle and MBM during 1979 to 2004. Comparing with the decreasing incidence of United Kingdom, the risk value is descending less than one of a million in 2005 and is acceptable now than before. The total risk of importing cattle from United States, Canada and Japan was 5.08E-12 in consideration of infected cattle rendering and producing MBM to feed cattle. For the purpose of evaluating maternal transmission, the simulation results are between 7.79E-14~1.09E-8. In view of the sensitivity analysis, the final risk value was most correlated by the rate of contaminated MBM to feed cattle. Consequently, noticing the BSE epidemic in the world and insisting ruminate feed ban is the most important risk control point.