Genetic diversity of bovine viral diarrhoea viruses (BVDV) in Denmark during a 10-year eradication period

A 243 base-pair fragment of the 5'- untranslated region (5'-UTR) of bovine viral diarrhoea virus (BVDV) was RT-PCR amplified from tissue samples (after one passage) or from plasma collected from Danish cattle in 1962 (1), 1993 (7), or in 2002-03 (28) when BVD was almost extinct as a result of a 6-year eradication programme. The PCR products were sequenced and phylogenetically analysed. All 36 samples were BVDV species I (BVDV-1), 29 sequences belonged to the BVDV Id subtype, 6 to the BVDV 1b subtype, and one sequence to the BVDV le subtype. While all samples from 1993 and 1962 were of Id subtype, the samples collected in 2002-2003 belonged to Id (22 samples), 1b (5 samples) and le (I sample) subtypes. In five herds, materials from two animals were obtained for PCR analysis. In four of five herds the sequences of the two viruses were identical, but in one herd the obtained sequences belonged to two different subtypes. Routine analysis detected I I PI calves older than 2 months of age. For early detection of infected calves it is recommended that antigen ELISA be replaced by PCR detection. Here we present the first sequence analysis of Danish BVDV strains.