Distribution pattern of bovine viral diarrhoea virus strains in intensive cattle herds in Italy.

The genetic variation of bovine viral diarrhoea virus (BVDV) was studied by comparative nucleotide sequence analysis of 26 Italian field strains collected during the period 1995-2000 in 18 cattle herds. A fragment within the 5'-untranslated region (UTR) was sequenced directly from gel-purified products obtained by reverse transcription polymerase chain reaction. BVDV-1b (n=14), -1c (n=1), -1d (n=1) and BVDV-2 (n=2) strains have been isolated. Most herds were infected by BVDV-1b. Pairwise similarity and cluster analysis of the remaining BVDV-1 isolates (n=8) did not provide a clear-cut assignation to defined BVDV-1 groups. This is the first time that a BVDV-2 isolation was reported in Italy. Among BVDV-2 reference strains, Italian BVDV-2 isolates showed the highest sequence similarity with the CD87 strain. Both BVDV-2 strains were isolated in two healthy animals from different herds. The 5'-UTR sequence of one of the two BVDV-2 strains was identical to a German BVDV field strain. Complete nucleotide homology was found only among BVDV strains isolated from the same herd, showing a herd-specific clustering. Moreover, 99.6% homology was observed between strains from herds linked by livestock trade. Despite the small number of BVDV isolates analysed, it revealed a high level of genetic diversity among Italian field BVDV strains.