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.
Subject(s)
Deer/parasitology , Encephalitis Viruses, Tick-Borne/physiology , Encephalitis, Tick-Borne/virology , Ticks/virology , Amino Acid Sequence , Animals , Base Sequence , Chlorocebus aethiops , DNA, Viral/chemistry , DNA, Viral/genetics , Ecology , Encephalitis Viruses, Tick-Borne/genetics , Encephalitis Viruses, Tick-Borne/isolation & purification , Encephalitis, Tick-Borne/epidemiology , Encephalitis, Tick-Borne/parasitology , Female , Italy/epidemiology , Male , Molecular Sequence Data , RNA, Viral/chemistry , RNA, Viral/genetics , RNA, Viral/isolation & purification , Reverse Transcriptase Polymerase Chain Reaction , Seasons , Sequence Homology, Amino Acid , Sequence Homology, Nucleic Acid , Tick Infestations/virology , Vero CellsABSTRACT
The most important tick-deer system potentially supporting the epidemiology of Lyme disease in the Italian Alps is that regarding Ixodes ricinus (L.) and roe deer (Capreolus capreolus L.). In this study, the pattern of tick infestation on 562 male roe deer harvested in September 1994 in 56 game districts of Trentino, Northern Italy, was assessed. The prevalence and density of infestation by I. ricinus were analyzed by a model based on classification and regression trees (CART), using both discrete and continuous variables concerning environmental and host parameters. The model discriminated attitude and host density as the 2 variables having the greatest effect on the prevalence and density of infestation of deer; the levels of infestation were higher at an altitude below 1125 m or at roe deer densities over 8.5 head per 100 ha. The density of tick infestation tended to be higher in older roe deer.
Subject(s)
Deer/parasitology , Ixodes , Tick Infestations/veterinary , Age Factors , Altitude , Animals , Arachnid Vectors , Disease Reservoirs , Italy/epidemiology , Lyme Disease/epidemiology , Models, Theoretical , Tick Infestations/epidemiologyABSTRACT
Cases of Lyme disease and tick-borne encephalitis were recognized recently in the Province of Trento, Italian Alps. Assessment of areas of potential risk for these tick-borne diseases is carried out by a model based on classification and regression trees (CART), using both discrete and continuous variables. Data on Ixodes ricinus (L.) occurrence resulted from extensive sampling carried out by standard methods in 99 sites over an area of approximately 2,700 km2 in the Province of Trento. A series of environmental parameters were recorded from each site and population densities of roe deer, Capreolus capreolus (L.), were considered. The CART model discriminates 2 variables that appear to have the greatest effect on the mesoscale occurrence of ticks: altitude and geological substratum, with a drastic decrease of tick frequency above an altitude of approximately 1,100 m and on volcanic substrata. The model is effective in identifying the mesoscale areas at greater potential risk, with a relatively low sampling effort.
