Evolutionary dynamics of Bovine Viral Diarrhoea Virus 1 (BVDV-1) in Italy: phylogeography and contact networks

Bovine Viral Diarrhoea Virus genotype 1 (BVDV-1) is a RNA virus (genus Pestivirus) with large impact on cattle worldwide, causing economic loss in dairy and meat production. 5’-UTR sequences of the three main BVDV-1 subtypes circulating in Italy were considered: 1b (n=139), 1e (n=134), 1f (n=50). Phylogeography was performed with BEAST1.8 grouping samples by areas of origin: Piedmont, Aosta Valley, Lombardy, Veneto, Emilia-Romagna regions and Center-Southern Italy. High similarity clusters were identified, and the relative sequences inputted in Outbreaker (R package) to simulate transmission chains. No significant geographic structure was observed in BVDV-1b tree, most of the sequences were from Lombardy and widely interspersed within geographically diverse clusters; subtype origin was traced to early XX century in Lombardy. BVDV-1e tree branched into three main clades and ancestry was estimated in Lombardy in 1990 (1988-1993). Piedmontese sequences clustered together, either due to later sample collection or to a recent introduction of BVDV-1e in Piedmont. BVDV-1f sequences clustered into three main clades, with a significant geographic structure: all Piedmont sequences clustered in two subclades, one including Aosta Valley sequences. Within high similarity clusters, viruses carrying identical 5´-UTRs were identified in different farms thus suggesting a common infection source or a between-farm transmission. Npro gene sequencing and epidemiological investigations are ongoing for confirmation. In conclusion, phylogeography and inferred contact networks suggest a regional transmission for 1e and 1f, while less evident for BVDV-1b. Understanding the origin and spread of BVDV is important for control strategies and prevention from introduction of new viral subtypes.