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

doi: 10.1292/jvms.17-0108 TI cattle. In non-vaccinated cattle and insufficiently immunized cattle, TI cattle would be produced with a probability of transient infection with BVDV (P t ). As there were few field data to verify P t , we referred to the simulated results of probability of transient infection by Damman et al. [13] . P t was considered to be common in all of the age groups, but would be affected by the P p , which was shown in the simulation analysis in Damman et al. P t was set as 25% of P p ; thus, the default P t was defined as 0.1%. Clinical manifestations: All of the probabilities of showing clinical manifestations of BVD were defined according to the opinions of field veterinarians in Nemuro. PI cattle of 0-2 M were assumed to be detected by apparent clinical manifestations of insufficient growth. In the present model, the probability that 0-2 M PI cattle being detected by clinical manifestations, P mp (0-2) , was set to approximately 80%. In parallel, a BVD cow that delivered its calf diagnosed as PI should be detected. The probability that >19 M PI cattle would be detected by clinical manifestations, P mp (>19) , was set to approximately 80%, with a hypothesis that 83% of the >19 M cattle deliver calves in a year. Although most of the PI calves were assumed to be identified during 0-2 M, some of the PI calves would be detected at a later phase, such as 3-8 or 9-14 M as insufficiently grown cattle. The probabilities that 3-8 and 9-14 M PI cattle would be detected by clinical manifestations, P mp (3) (4) (5) (6) (7) (8) and P mp (9) (10) (11) (12) (13) (14) , respectively, were set to approximately 40% and 20%, respectively. On the other hand, PI cattle of 15-18 M were assumed to be rarely detected by clinical manifestations since the older the PI cattle, the fewer signs they are expected to show, besides reproductive disorder. Transient infection of BVDV in cattle is mainly subclinical or clinical over a short period. In the present model, TI cattle from the >19 M group would only be detected by reproductive disorder with a probability of 30%, which was derived from the rates of calving in delivered cattle, and delivery of the PI calf as an immature fetus would be caused by BVDV infection over 33% of the gestation period. We did not assume the presence of other reproductive disorders, including conception failure and abortion, as these are also caused by other infectious diseases, non-infectious diseases, or environmental factors.