Survey for detecting persistently infected cattle with bovine viral diarrhea in Japan.

To establish effective and efficient control measures for bovine viral diarrhea (BVD) in Japan, a pilot survey on persistently infected (PI) animals in dairy farms was conducted. A total of 5,949 cattle from 79 farms in 11 prefectures were tested; seven cattle in six farms were identified as PI animals. The proportion of farms with PI animals in Japan was calculated as 7.6% (95% confidence interval: 3.1-16.4%), and proportion of cattle tested as PI animals was 0.12% (95% confidence interval: 0.05-0.25%). The presence of only one or two animals in PI positive farms suggested the application of screening tests covering almost all cattle in each farm using pooled serum or bulk milk could be effective for implementing a large-scale survey for detecting PI animals.