Estimating the BSE infection and detectable prevalence in cattle born after 2000 in Japan

We estimated the infection prevalence of BSE in Japanese cattle born in the period 2000-2012, using maximum likelihood methods and BSE surveillance data of these birth cohorts. From this, we predicted the number of infected cattle and test positives in years 2004-2020. Assuming that the infection prevalence decayed exponentially over time from 2000, the infection prevalence of the 2000 birth cohort was estimated to be 0.00058 which declined exponentially by 0.115 times per year in the following years. The number of infected cattle was calculated to have peaked in 2005 and would be zero by 2020. The number of test positives was calculated to have peaked in 2005 and would be zero by 2012. The number of BSE cases actually detected was within the 95% confidence interval of the predicted numbers. The detectable prevalence (predicted number of test positives/number of cattle tested) was predicted to be highest in 2005. In this year it was predicted that one animal out of 160,000 tested would test positive. The detectable prevalence would decline exponentially to zero in the subsequent years.