Provision of precise estimates of number of cattle infected as accurate as possible is important for dealing with control measures of bovine spongiform encephalopathy (BSE) in Japan. We extended backcalculation in order not only to estimate but also to interpret its present epidemiology. Results in previous studies in the UK were used for critical probability density functions such as the incubation period of BSE, age dependent susceptibility, and survivorship function of cattle. Based on eleven confirmed BSE cases, including and excluding two atypical cases, four possible trajectories, which proposed between two to eighteen cases until the year 2010 with reasonable 95 % prediction intervals, were obtained under different assumptions. Through the use of the age-stratified method, it was considered the major feed risk had been concentrated mainly in 1996 and thereafter was at a much reduced level. Technical matters in the application of backcalculation for a highly sparse record were discussed.

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We experienced bovine viral diarrhea virus (BVDV) infection in 37 farms located in Yubetsu-town, Hokkaido, between April 2001 and March 2004. Fifty-eight persistently infected (PI) cattle were found after blood examination of whole herd in 28 farms of them. PI cattle is produced by fetal infection with NCP BVDV between 40 and 125 days of gestation, and in this study we performed an epidemiological investigation in presuming the period of BVDV epidemic from birth of PI cattle. In addition, we performed a questionnaire survey about farming, feeding and husbandry for all dairy farmers, and evaluated the risk factors related with BVDV infection by using the logistic regression model. We found no relationship between BVDV epidemic and season or region, and we also found the BVDV epidemic patterns that multiple PI cattle were produced from single epidemic period, and that the birth of PI cattle brought down another BVDV epidemic for the subsequent PI cattle. As a possible risk factor, participation of a show cattle competition, purchased cattle, feeding grass silage and the dehorning method were suspected. In future, we have to clarify the causal relationship between BVDV infection and these risk factors, and we suggest that show cattle need a vaccine and the examination for BVDV, in addition, the BVDV examination is essential for not only purchased cattle but also for their offsprings.

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