Bovine spongiform encephalopathy in Japan and options for control

Since September 2001, Japan has reported to the World Organisation for Animal Health (OIE: Office International des Epizooties) 31 cases of typical bovine spongiform encephalopathy (BSE) and two atypical cases. There were at least two major exposure episodes in Japan. The first, attributed mainly to imported contaminated feed ingredients, occurred between 1995 and 1996 and 13 affected Holstein cows (Group A) were detected in different parts of Japan. The second exposure occurred in Hokkaido, the northernmost island of Japan, between 1999 and 2000. To date, 14 BSE cases (Group B) have been found there. All positive cases of Groups A and B were Holstein cows. The remaining four cases (Group C) were of various ages, including one atypical case of 169-month-old native beef cattle, but the sources of infection are not yet known. Two young (21- and 23-month-old) Holstein steers are also included in Group C, but the transmissibility of these cases has not been confirmed. It appears unique that all confirmed typical BSE cases in Japan have been in Holstein cows, and it could be suggested that future surveillance of BSE in Japan should be focused solely on Holstein cows. It is also suggested that Japan be divided into two zones; Hokkaido zone and the rest. In this way, different strategies could be implemented to achieve eradication within shorter periods of time in respective zones. Since the youngest typical BSE case confirmed in Japan was a 48-month-old cow belonging to Group B, it is suggested that the age of the cattle to be tested at abattoirs be raised from 20 months to 30 months and older. So far, two so-called 'atypical' cases of BSE have been found in Japan, and the author proposes that it is necessary to demonstrate the transmissibility of these cases in order to confirm that they are indeed transmissible spongiform encephalopathies. Further, the author considers it necessary to compare the standards of the national diagnostic laboratory that tests healthy cattle in Japan with those of other OIE BSE reference laboratories in order to demonstrate that current Japanese diagnostic practices meet international standards.