Lars Tälleklint

Geographical distribution, host associations, and vector roles of ticks (Acari: Ixodidae, Argasidae) in Sweden

Abstract 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 Haemaphysails 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 satiguineus (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.

Lyme borreliosis spirochetes in Ixodes ricinus and Haemaphysalis punctata ticks (Acari: Ixodidae) on three islands in the Baltic Sea

The prevalence of infection with Lyme borreliosis spirochetes in nymphal Ixodes ricinus and Haemaphysalis punctata was examined on three Swedish islands in the Baltic Sea. The proportion of H. punctata nymphs infected with Borrelia spirochetes (≈2%) was lower than that of I. ricinus nymphs (11–16%), even on the island of Stora Karlsö where both tick species feed on the single mammalian host present, the varying hare, Lepus timidus. Ten of the 12 infected questing H. punctata nymphs harboured very few spirochetes, whereas the remaining two harboured as many as 30–40 spirochetes. However, it remains to be seen whether H. punctata nymphs are capable of transmitting spirochetes during their blood meal and, thus, serving as vectors for Lyme borreliosis spirochetes. On Gotland and Fårö, I. ricinus was more abundant than H. punctata in deciduous and coniferous forest, whereas H. punctata was equally or more abundant than I. ricinus in juniper brush areas on open land. Host preference and biotope usage of H. punctata seems, in general, to prevent this tick from feeding on highly infective Borrelia reservoirs, such as Apodemus mice.

Control of Lyme borreliosis in Sweden by reduction of tick vectors: An impossible task?

During the last decade, much research on control strategies against the primary vector,Ixodes scapularis, of Lyme disease in northeastern USA has been carried out. This has included work on biological or chemical control, habitat modification, and reduction of host availability. In this paper we evaluate the possibility of using these methods for control of the primary vector of Lyme borreliosis in Sweden,I. ricinus. It is emphasized that in Sweden people mainly contract Lyme borreliosis in woodlands and forests. Because of the enormous size of the area that would need treatment, general application of acaricides and habitat modification may not work well in Sweden. Another possible method is to reduce the availability of tick hosts. This method can be targeted at species that are essential for tick reproduction or at hosts that are capable of infecting ticks withBorrelia burgdorferi. On isolated Swedish islands where few mammal species are present, reduction of the main or only reservoir host may effectively control Lyme borreliosis. On the Swedish mainland, however, at least four common mammal species are important blood-hosts to femaleI. ricinus, and at least eight common mammal species are competent reservoirs forB. burgdorferi. Sufficient reduction of host availability may therefore not be achieved here without killing vast numbers of mammals. In general in Sweden, the most effective method of preventing Lyme borreliosis seems to be to inform people about how to dress in risk areas, and that daily checks for ticks with prompt removal of attached ticks drastically reduces the infection risk.