Evaluation of control measures for bovine viral diarrhea implemented in Nemuro District, Hokkaido, Japan, using a scenario tree model

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

It is estimated that immediately after initiating the mass vaccination program, the prevalence of BVDV is not low. Therefore, monitoring of infected cattle in parallel with the implementation of mass vaccination should be an effective intervention to reduce the risk of BVD in the population. In Nemuro, an individual test using a serum sample is mandatory applied to all cattle that use communal pastures [29] . In Japan, the use of communal pasture for summer grazing is common in any age of dairy cattle, including pregnant cows; therefore, the spread of BVDV infection horizontally or vertically in communal pastures has been suspected. An individual test prior to communal pasture grazing can detect young PI heifers that normally rarely show clinical manifestations; however, there are practical difficulties associated with adopting this test for a larger number of targeted cattle. On the other hand, the bulk tank milk test can be applied for a large number of animals, and some of the reports have already evaluated the efficacy of the bulk tank milk test [4, 18, 21] . As the target of the bulk tank milk test is lactating cows, this test is unlikely to detect the young PI heifers. Given that adoption of mass vaccination cannot contribute to a decrease of PI animals in the population, the individual test rather than the bulk tank milk test is more effective to reduce PI cattle immediately after conducting the mass vaccination. This consideration may support the results showing that the efficacy of the individual test with a lower coverage was equal to that of the bulk tank milk test in the present study. Comparison of efficacies between the individual test and screening test appears to be affected by some factors, including test sensitivity, virus prevalence, and distribution of targeted animals. Input of suitable data to the disease model as well as collection of accurate data in the field is necessary to reach a confidential output so as to contribute to the selection of a more effective intervention.