Bovine spongiform encephalopathy (BSE) in Japan

Bovine spongiform encephalopathy (BSE) has become an important problem not only for the animal industry, but also for public health. BSE was first recognized in Japan in September 2001 as a result of fallen stock surveillance. Since October 2001, all cattle slaughtered at abattoirs have been tested for BSE. From April 2004, examination of all dead cattle aged over 24 months has been conducted at livestock hygiene service centers. Samples positive on enzyme linked immunosorbent assay (ELISA) are further subjected to western blot (WB) and immunohistochemistry (IHC). Fourteen BSE cases had been reported by November 2004; thirteen were classified as the typical form while the other was atypical. Variant forms of BSE with atypical histopathological and/or biochemical phenotype have also been reported in Italy and France. Further study is required to characterize the BSE prion, and to this end, brain homogenates from Japanese BSE cases were intracerebrally inoculated into wild-type mice. The first case diagnosed in Japan (BSE/Chiba) has been successfully transmitted to rodents. Mean incubation period (409.0 +/- 28.2 days) was considerably longer than that previously reported. PrPSc distribution, possibly due to prion titer, recipient susceptibility and/or sample storage conditions. Transgenic mice that overexpress a bovine PrP gene were recently introduced to overcome the species barrier problem, hopefully enabling accelerated transmission of BSE prions. These transgenic mice are also being used in ongoing transmission studies of the atypical BSE case.