Tick-borne encephalitis virus in northern Italy: molecular analysis, relationships with density and seasonal dynamics of Ixodes ricinus

Ixodes ricinus ticks were collected from dragging vegetation and from shot roe deer in the province of Trento and Belluno in northern Italy. Ticks wer e pooled for analyses and from 1060 pools of ticks collected in the provinc e of Belluno and 12 390 tick samples collected in Trentino, four proved pos itive by immunofluorescence microscopy using a tick-borne encephalitis (TBE )-specific antiserum. The identity of the virus isolates was determined by RT-PCR cycle sequencing and they were all found to be closely similar (> 98 % nucleotide identity) to typical western European TBE complex viruses as f ound in Austria. The isolates from Trentino differed from the Neudorfl stra in of western European TBE virus at eight nucleotide positions but as these nucleotide substitutions were all synonymous, there were no amino acid cha nges. These results imply that the virus isolates in Trentino have changed slightly from the typical European strains isolated in nearby Austria. The abundance of questing ticks and ticks feeding on roe deer was greater in TB E positive hunting districts than in hunting districts ZD where TBE complex viruses were only probable or believed to be absent. In TBE positive and p robable districts synchrony in the seasonal dynamics of larvae and nymphs o f I. ricinus was observed. This study provides evidence to suggest that roe deer may have an important role to play in the maintenance of tick density and in the persistence of TBE virus.