INCREASING GEOGRAPHICAL-DISTRIBUTION AND DENSITY OF IXODES-RICINUS (ACARI, IXODIDAE) IN CENTRAL AND NORTHERN SWEDEN

3 The geographical distribution and density of Ixodes ricinus (L.) in the 2 northern regions, Svealand and Norrland, in Sweden were studied by using a questionnaire in Swedish magazines for house owners and dog owners, and in provincial newspapers. Analysis of the approximate to 1,200 answers revealed that ticks are present in all parts of Svealand (except northern Varmland and northern and western Dalarna), the sout heastern part of Norrland (i.e., Gastrikland and Halsingland), and alo ng the Baltic Sea coast of central and northern Norrland. The proporti on of answers reporting ticks and the estimated tick density (i.e., th e number of ticks infesting dogs and cats) decreased from south to nor th. The answers to the questionnaire and data from field sampling of t icks suggest that tick density decreased distinctly along a narrow bou ndary zone, coinciding with the biological limit of Norrland (Limes No rrlandicus), crossing Sweden through southern Varmland, southeastern D alarna, and central Gastrikland. The results of the questionnaire sugg est that I. ricinus ticks are more widespread today than in the early 1980s, especially in Varmland, western and central Dalarna, Halsinglan d, and the coastal areas of Medelpad, Angermanland, and Vasterbotten, and that the proportion of the human population at risk for tick-borne pathogens in Svealand and Norrland is increasing.