台灣牛隻因進口北美地區帶骨牛肉引入牛海綿狀腦病之量化風險評估

Abstract

本研究的目的為評估自北美地區進口帶骨牛肉而造成台灣牛隻牛海綿狀腦病 (bovine spongiform encephalopathy, BSE)之風險。BSE發生地區的帶骨牛肉可能含有骨髓、骨附屬物及屠宰過程遭受脊髓與背根神經結等污染之風險物質，對牛隻具有感染威脅，本研究因此建構一風險評估模式，除了評估自北美BSE發生地區引入之風險外，亦可使用於其他相關國家進口牛肉產品之風險評估。模式首先考量北美地區之BSE盛行率與可能輸入台灣之帶骨牛肉進口量，再考慮帶骨牛肉釋出後在台灣之使用與處理，如廚餘回收、加工及屠宰廢水系統、化製產品及回收再製產品等，而終致進入牛隻環境，由牛隻之經口暴露劑量與年齡感受性等關係，評估牛隻感染BSE之機率。本研究以指數分布推估動物飼料中肉骨粉受污染的機率，認為骨髓為主要的BSE感染力來源，此外亦將豬隻媒介BSE的可能納入風險評估模式中。模式經最適篩選及參數設定後，使用Latin Hypercube模擬重覆測試10,000次，結果顯示2010年進口北美地區帶骨牛肉造成台灣BSE風險為3.08×10-11 ± 2.75×10-10 (第95百分位為4.39×10-9)。敏感性分析顯示有機肥為模式中重要的風險傳播途徑。雖然推估出之風險值低於一般認定之可忽略風險範圍，但模式中的不確定性高，進一步的參數確認與模擬有其必要，而針對此不可逆的致死性人畜共通傳染病，嚴謹的風險管理仍屬必要。

The study aims to assess bovine spongiform encephalopathy (BSE) risk of Taiwan incurred from North America (NA) bone-in beef importation which introduces risk materials including internal bone marrow as well as external spinal cord and dorsal root ganglia contamination. After importation, releasing of risk materials comes from plate waste recycling, processing factories and slaughterhouse wastewater treatment as well as rendered product input into cattle environment. A risk model is constructed to simulate BSE prevalence of NA, the estimation of product usage and distribution, and the probability of cattle oral transmission. After input the estimated values for all parameters and selection the most appropriate model, Latin Hypercube simulation for 10,000 times is conducted and the results reveal that the risk of BSE through importing NA bone-in beef is 3.08×10-11 ± 2.75×10-10 (95th percentile = 4.39×10-9) in 2010. The study provides not only a scenario of overall bone-in beef importation risk assessment for domestic cattle but also a flexible model to assess the BSE risk from other beef exporting countries. Moreover, the study introduces a new idea to extrapolate meat and bone meal contamination in animal feed via exponential distribution, takes bone marrow as the major resource of infectivity to process risk assessment, and considers the role of pigs in transmission of BSE. The results show that fertilizer is the most important routes of BSE transmission in our model. Although the simulated risk values are within negligible ranges of scientific acceptable scale, they should be interpreted carefully for the sake of uncertainties in current model. Thus, it is necessary to ascertain all the ambigulous parameters in current model and process for further simuations to adjust the risk in the future. Since BSE is an irreversible fatal zoonotic disease, it is essential to establish rigorous strategies through appropriate risk management to reduce BSE transmission risk.