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

According to the latest large-scale survey in Japan, seven cattle on six farms tested positive for persistent infection with BVDV among 5,949 cattle from 79 farms analyzed, resulting in 7.59% (95% CI: 3.1-16.4%) of farms comprising PI animals and 0.12% of cattle being PI (95% CI: 0.05-0.25%) [21] . Four out of six affected farms had not implemented vaccination for one year, and none of the seven PI animals had been vaccinated, indicating that non-vaccination may be a major factor in Japan for persistent BVDV infection in cattle. In addition, the fact that most of the PI animals in the above-mentioned survey were detected in heifers implies the importance of monitoring heifers for BVD control as high priority. Given these points, we aimed to develop scenario models to monitor non-vaccinated animals and/or heifers intensively but cheaply. The results obtained in this study confirmed the efficacy of compulsory testing of introduced animals, and targeting heifers and/or non-vaccinated cattle rather than all cattle, should be sufficient to be efficacious and highly cost effective if BTM tests are implemented concurrently. In addition, more effort might be required to arrange a system to register introduced animals with minimum necessary information including vaccination status, possibility of pregnancy as well as cattle ID in order to grasp the animal introduction accurately. Although BTM testing contributes less to the detection of introduced animals, it should be regarded as a very powerful tool to monitor the entire population inexpensively, and in general, the proportion of lactating cattle to the entire population is much larger than that of introduced animals. In Japan, BTM tests are used for the detection of BVDV genome, which is differing from well-developed antibody detection system in Europe. The effectiveness of BTM tests using antigen monitoring has been widely recognized and reported [20] [21] [22] ; however, this effective and cheap monitoring program cannot be applied to beef cattle population. Hence, the prevalence of BVD animals in the beef cattle population in Japan might have seldom been reported. A monitoring program for BVD in beef cattle also needs to be developed to confirm the BVD prevalence among these herds. In this study, it was observed that lower BVDV prevalence resulted in smaller gaps in vaccination coverages with respect to both the number of detected and missed animals (Fig. 3) . Ultimately, under very low BVDV prevalence, the monitoring effectiveness at 0% of vaccination coverage was not apparently different from that at 100%. These findings may trigger suggestions for reviewing implementation of compulsory testing to introduced non-vaccinated animals because, under very low BVDV prevalence, the efficacy of compulsory testing would be rarely affected by vaccination coverage. It indicates, if efficacy of monitoring programs were not different, many of stakeholders might select the cheaper program to decrease financial burdens. However, this change would require intensive discussion with convincing scientific evidence because it should be implemented under the hypothesis that the very low prevalence of BVDV is maintained by proper biosecurity measures with different stakeholders in outside of the target area. Otherwise, BVDV would spread rapidly among sensitive cattle in outside of the target area that has not been conferred enough immunity to prevent its re-infection by vaccination, and then might be introduc