Simulating the bovine spongiform encephalopathy situation in Japan.

Despite various measures taken by the Japanese government to protect the cattle population from exposure to the bovine spongiform encephalopathy (BSE) agent, the first case of BSE was detected in September 2001. Subsequently, BSE surveillance was enhanced, involving mandatory reporting and investigation of all clinical BSE suspects, and testing of fallen stock and all cattle slaughtered for human consumption. Tests on over nine million cattle led to the detection of 35 additional cases by the end of May 2009. Using the surveillance data and other information as input variables, models were developed to explore the possible source of introduction of BSE into Japan, evaluate the effectiveness of control measures, estimate the prevalence of BSE in different birth cohorts, predict a future BSE epidemic, and simulate the impact of changes in surveillance strategies. Despite difficulties associated with the availability and uncertainty of some of the input variables, these models provided an objective insight into the BSE situation in Japan.