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

Abstract

Ixodes ricinus ticks were collected from dragging vegetation and from shot roe deer in the province of Trento and Belluno in northern Italy. Ticks were pooled for analyses and from 1060 pools of ticks collected in the province of Belluno and 12390 tick samples collected in Trentino, four proved positive 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 found in Austria. The isolates from Trentino differed from the Neudorfl strain of western European TBE virus at eight nucleotide positions but as these nucleotide substitutions were all synonymous, there were no amino acid changes. 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 TBE positive hunting districts than in hunting districts where TBE complex viruses were only probable or believed to be absent. In TBE positive and probable districts synchrony in the seasonal dynamics of larvae and nymphs of L. 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.

Prevalence and genetic variability of tick-borne encephalitis virus in host-seeking Ixodes ricinus in northern Italy

“…The Bayesian phylogenetic analyses provide results that are consistent with those of previous studies, indicating that the new Italian TBEV sequences generated here belong to the European TBEV subtype (Hudson et al, 2001;D'Agaro et al, 2009). Interestingly, we found a substantial amount of genetic divergence between these Italian TBEV sequences, despite both the relatively short E gene sequence fragments analysed and the restricted geographical range (Trento province only).…”

“…Interestingly, we found a substantial amount of genetic divergence between these Italian TBEV sequences, despite both the relatively short E gene sequence fragments analysed and the restricted geographical range (Trento province only). Comparison of the sequences at the nucleotide and amino acid levels showed that this variability is mostly caused by synonymous substitutions, as observed previously by Hudson et al (2001). In particular, we found that, whilst six synonymous substitutions separate the two Italian sequences, only one nonsynonymous substitution was observed, at aa 513, where ITTN 2006 6-7 has a glutamine and ITTN 2006 12-8 has a lysine (see Table 1).…”

“…Furthermore, the incidence of TBE in these regions has increased from 0.06 to 0.88 cases per 100 000 inhabitants in the same time frame (Rizzoli et al, 2009). Importantly, TBEV has been isolated and identified in most of the regions where human cases have been reported (Hudson et al, 2001;Beltrame et al, 2006;Cruciatti et al, 2006;Floris et al, 2006;D'Agaro et al, 2009). However, previous studies undertaken primarily in the Veneto and Trentino regions have shown a lower prevalence of TBEV in Italian tick populations compared with other European sites where TBEV is endemic (Hudson et al, 2001), whilst phylogenetic analyses indicate that only strains of the European subtype very similar to the Austrian Neudoerfl strain have been found in Italian TBEV populations (Hudson et al, 2001;Floris et al, 2006;D'Agaro et al, 2009).…”

Empirical evidence for key hosts in persistence of a tick-borne disease

“…Our study was carried out at the Southern edge of the TBE virus distribution, in an isolated TBE focus (Hudson et al, 2001). The area is located in Valle dei Laghi, Trentino (grid reference, 1652050E 5093750N) in the north-eastern Italian Alps.…”

Investigating the loss of recruitment potential in red grouse (Lagopus lagopus scoticus): the relative importance of hen mortality, food supply, tick infestation and louping-ill

“…In the Scottish uplands, the complexity of the system is illustrated by the wide range of tick hosts including sheep (Ovis aries L), red deer (Cervus elaphus L), mountain hare (Lepus timidus L) and red grouse (Lagopus lagopus scoticus L) (Gray et al 1992;Hudson et al 1997;Hudson et al 2001;Laurenson et al 2003). Of particular interest is the impact that the sheep tick may have on red grouse, an economically important gamebird, which has been in long term decline (Shaw et al 2004).…”