Abstract
For the identification of herds with cattle persistently infected (PI) with bovine viral diarrhea virus, 1,272 animals from 20 herds were subjected to serum neutralizing (SN) test using the Nose strain and virus isolation. Eighteen PI cattle were detected from 5 herds. On the phylogenetic tree based on the nucleotide sequences of the 5' untranslated region, the isolates from the PI cattle were classified into genotypes-1a or -1b. Of 3 unvaccinated calves aged 6 to 12 months selected from each herd, the probabilities of obtaining 2 or more non-PI cattle with SN antibody titers of 64 or more (PSN), one or more PI cattle (PVI), and either of the conditions (PTotal) were calculated using the hypergeometric probability model. PTotal for the 5 herds with PI cattle was 1.000. PSN for 3 herds with many PI cattle within the selected age group was as low as 0.500 or less, and PVI was as high as 0.886 or more. PSN in the 2 other herds with few PI cattle was 1.000, and PVI was as low as 0.375 or less. PTotal in 13 of 15 herds without PI cattle was 0.000, and was 0.714 or 0.774 for the 2 other herds. These results suggest that herds with PI cattle can be predicted with high accuracy when both SN test and virus isolation are performed on only 3 unvaccinated calves aged 6 to 12 months selected from a herd.
