Assessment of the cost effectiveness of compulsory testing of introduced animals and bulk tank milk testing for bovine viral diarrhea in Japan

ISODA, Norikazu; ASANO, Akihiro; ICHIJO, Michiru; OHNO, Hiroshi; SATO, Kazuhiko; OKAMOTO, Hirokazu; NAKAO, Shigeru; KATO, Hajime; SAITO, Kazuma; ITO, Naoki; USUI, Akira; TAKAYAMA, Hiroaki; SAKODA, Yoshihiro

To evaluate the reduction of BVD risk and determine the prevalence of BVD after continuous implementation of the control measure, the scenario models were continuously run. We assumed that the missed cattle in the simulation would be the BVD cattle remaining despite a set of all control measures for an entire year and would be the source of BVDV infection in the next year. The sum of the proportions of missed animals despite a set of all control measures in a scenario and of estimated natural infections per 10,000 animals was regarded as the expected prevalence of BVD among the inherent cattle in the target area in the next year. The estimated number of natural infections was calculated based on the rate of naturally infected herds in a study by Santman-Berends et al. using field data regarding local risk factors of BVD infection in a study by Kadohira et al. [20, 34] . The number of estimated natural infections in this study was set as the product of the number of missed animals and 0.02, which was defined as the natural infection parameter per BVD cattle. Practically, a set of 5%, 50%, and 95% percentiles of the sum of the missed animals and expected natural infections were calculated in each simulation and used for the probability of persistent infection among inherent cattle in the next year as the lower limit, median, and upper limit, respectively. On the other hand, probability of persistent infection among introduced cattle to the target area was fixed at 0.4% [RiskPert (0.003, 0.004, 0.005)], which was a default setting. Simulations of each control measure were repeated 15 times with a change of probability in persistent infection.