BSEサーベイランスの推移

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Since September 2001, Japan has reported 35 BSE cases to the OIE including a few atypical cases. There were at least two major exposures in Japan. The first exposure to BSE occurred between 1995 and 1996, and 13 Holstein cows (Group A) have been detected in different parts of Japan due mainly to imported contaminated feed ingredients.The second exposure occurred in Hokkaido between 1999 and 2001. As of April 2008 17 BES cases have been found there among the same cohort animals (Group B). Almost all positive cases of Groups A and B were Holstein cows. The remaining 5 cases (Group C) were of various ages including two native beef cattle. Two young (21and 23-month-old) Holstein steers are also included in Group C, but the transmissibility of these two cases has not been reported. Additional data on these 2 cases are needed to confirm that these were genuine BSE cases.There were 4 cases in native Wagyu breed. Two were in Hokkaido among Group B cases, and the other two were old Wagyu (13 and 15 years of age) of Group C. It will be possible that future surveillance of BSE in Japan could be focused mainly in Hokkaido where a large number of Group B cohort cattle still remain. It will be also possible that Japan is divided into two zones, Hokkaido zone and the rest. Since the youngest typical BSE case confirmed in Japan was a 48-month-old cow of Group B, it is considered that the age of the cattle to be tested at abattoirs could be raised from 20 months to 36 months or older with negligible risks.Three atypical cases of BSE have been found in Japan, but it is considered necessary to demonstrate the transmissibility of these cases in order to confirm that they are indeed TSE cases. So far only one case (No. 24) could be transmitted to mice. The author considers that it is necessary to review the surveillance systems in Japan with reference to the OIE standard for BSE surveillance. It is also considered necessary that more countries to look for atypical BSE cases in order to obtain enough data necessary for the OIE to define international rules dealing with atypical BSE cases.
獣医疫学会の論文

BSEサーベイランスの推移

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