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

Implementation of appropriate interventions such as a mixture of mass vaccination and the individual test resulted in the decrease of numbers of PI animals in all the age groups. As the remaining PI cattle in the herd are known to be a source of new infection of BVDV in the herd, and may produce PI calves, we should aim to detect as many PI and TI cattle of any age as possible for the BVD eradication in the area by performing screening rather than individual tests. However, if animal-level prevalence of BVD becomes lower, it would be likely that the cost-effectiveness of the screening test using bulk tank milk would be higher due to lower between-herd prevalence. This would be because implementation of outbreak investigation could eradicate the BVD cattle in premises, thereby decrease of BVD cattle would affect to between-herd prevalence but not to within-herd prevalence in infected premises. In the situation of a higher number of herds being free from BVD under a very low prevalence of BVD, we could save resources by investigating non-infected herds while ensuring the sensitivity for detecting infected cattle by implementing an outbreak investigation once the infected herd is detected by the screening test. The decision to switch between implementation of the individual and screening test is critical so as to achieve risk management with high cost-effectiveness. In further analysis, the scenario model with more detailed conditions should be run to compare the outputs both at hygiene level and cost-effectiveness.