This review covers the geographic distribution and host relationships of the tick species in Sweden. Ixodes uriae White, I. caledonicus Nuttall, I. unicavatus Neumann, I. arboricola Schulze & Schlottke, and I. lividus Koch are ornithophagous species. I. trianguliceps Birula, I. canisuga Johnston, I. hexagonus Leach, and Argas vespertilionis (Latreille) are mammalophagous. I. ricinus (L.) and Haemaphysalis punctata Canestrini & Fanzago feed on both birds and mammals. All these tick species may be considered to be permanently present in Sweden. I. persulcatus Schulze, Hyalomma marginatum Koch, and the brown dog tick, Rhipicephalus sanguineus (Latreille), may be regarded as not indigenous to Sweden although they may be regularly introduced by spring-migrating birds or imported dogs, respectively. The first European record of the American dog tick, Dermacentor variabilis (Say), is reported. There are several records of Hyalomma aegyptium (L.) from imported tortoises in Sweden. Excluding other ticks imported on exotic pets and zoo animals, another 13 tick species are listed that may occur, at least occasionally, in Sweden. Because of its wide geographic distribution, great abundance, and wide host range, I. ricinus is medically the most important arthropod in northern Europe. I. ricinus is common in southern and south-central Sweden and along the coast of northern Sweden and has been recorded from 29 mammal species, 56 bird species, and two species of lizards in Sweden alone. The potential introduction to Sweden of exotic pathogens with infected ticks (e.g., I. persulcatus and H. marginatum on birds or Dermacentor spp. and R. sanguineus on mammals) is evident.

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Combined network equilibrium models of trip distribution, modal split, and route choice are formulated and estimated for the Stockholm region. These models take into account the feedback effects among three stages of the classical four-step model. A simultaneous structure of the mode and destination choices is studied together with nested combined models reflecting conditional choice probabilities. In the traditional combined model, mode choice is assumed conditional on destination choice. The reverse combined model, in contrast, considers destination choice conditional on mode choice. User-optimal traffic assignment is integrated with these approaches to modeling travel demand in network equilibrium models. The three combined models are estimated using the full-information maximum likelihood technique implying that all preference parameters are estimated simultaneously. The models are estimated on medium-size travel and network data for the Stockholm region in 1986. The results suggest a rejection of the traditional nested model because of incorrect relative values of the estimated cost-sensitivity parameters. The reverse nested model is preferred, even if the overall goodness-of-fit is better for the traditional nested model. An application to a future scenario for the year 2020 is included.

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