馬肉中に含まれる住肉胞子虫の危害性消失条件の検討による生食用馬肉を共通食とする食中毒事例の発生防止対策に関する研究

摘要

熊本県では,馬刺しを共通食とする原因不明の一過性嘔吐下痢症事例が最近3年間で毎年27件以上発生していた.同事例の原因はSarcocystis fayeri住肉胞子虫で,本研究では一定時間の冷凍処理で住肉胞子虫のシストがぺプシンにより消化されその毒性を失うことを見いだした.同胞子虫シストを含んだ馬肉を-20℃で48時間以上冷凍したところ，シスト由来の毒性タンパク質の消失も確認された.本研究で確立した冷凍条件を用いての冷凍処理の普及により，平成23年10月以降，馬刺しが原因と考えられる食中毒の発生報告はなく,この冷凍処理基準が，馬刺しによる食中毒防止対策として有効であることが示唆された.%More than 27 outbreaks per year of food poisoning caused by consuming horse meat were reported in Kumamoto Prefecture (including Kumamoto City) from January 2009 to September 2011. It was found that the causative agent of the outbreaks was a protein with a molecular weight of 15 kDa that had originated from bradyzoites of Sarcocystis fayeri parasitizing the horse meat. Rabit ileal loop tests showed that pepsin treatment of homogenates of frozen horse meat containing the cysts of S. fayeri induced loss of toxicity, presumably by digestion of the proteinous causative agent (s). Slices of horse meat containing the cysts were frozen at below -20℃ for various periods. The cysts were collected after thawing the slices, then treated in an artificial stomach juice containing pepsin. The bradyzoites of the cysts kept at - 20℃ for 48 hr or more completely disappeared. Simultaneously, the 15 kDa protein also disappeared in the frozen cysts. After notifying the public and recommending freezing treatment of horse meat, no subsequent cases of food poisoning were reported. This indicates that freezing of horse meat is effective to prevent the occurrence of food poisoning caused by consuming raw horse meat containing S. fayeri.