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

To estimate the number of detected and missed cattle infected with BVDV as transient and persistent infection, we developed a stochastic scenario tree model composed of nodes representing cattle categorization, immunity, virus infection, and monitoring based on implementation in a certain area in Nemuro District, Hokkaido Prefecture, where the cattle infected with BVDV had been reduced by the interventions [29] . A scenario tree model for risk assessment is generally composed of three types of nodes, namely category nodes, infectious nodes, and detection nodes, so as to theoretically calculate the probabilities of infected animals being detected at a given level of prevalence. To generalize the output of this model, the number of initial cattle was set as tens of thousands instead of the actual number of cattle in Nemuro. The numbers of either persistent or transient infection with BVDV in each animal category were calculated as a product of all conditional probabilities describing the nodes of each specific categorization and infection pathway. The overall probabilities of detecting and missing cattle persistently or transiently infected with BVDV (BVD cattle) through the monitoring nodes as interventions for BVD control in a default or scenario settings were calculated as a product of the probabilities of infection and all conditional probabilities describing the nodes of each specific detection pathway. The total numbers of detected and missed BVD cattle were calculated as an output of the default or scenarios and were compared to evaluate the efficacy of the interventions in the scenarios. The scenario tree was developed in an Excel spreadsheet (Microsoft Office Excel 2013), using the software @Risk 6 (Palisade Corporation, Ithaca, NY, U.S.A.), and was run using 10,000 iterations.