The most common tick-borne disease in humans is Lyme borreliosis. Extensive field and laboratory tests have revealed that the Borrelia bacterium is present in a larger proportion of ticks than has been shown by earlier studies. Another finding is that migratory birds play an important role in the spreading of ticks and pathogenic agents borne by ticks.
Ticks are to be found in most parts of the world, and more than 900 species have been identified so far. The geographic distribution of these many tick species varies and the most prevalent species in Norway is the forest tick (Ixodes ricinus), which can be the bearer of a number of bacteria and viruses that can infect animals and humans and cause disease.
In recent years, there has been increasing focus on ticks and the diseases a tick bite can cause and there are also indications that ticks are occurring in new areas of the country. This has resulted in an increase in the number of disease cases, both as regards Lyme borreliosis (LB) and other illnesses such as tick-borne encephalitis (TBE).
As part of her doctoral research at The Norwegian School of Veterinary Science, Vivian Kjelland has carried out extensive field and laboratory studies with a view to increasing our knowledge in this field. She has examined the occurrence of Borrelia burgdorferi sensu lato (s.l.) in ticks and which genotypes of the bacterium occur in ticks in Norway. Her results show that a larger proportion of the ticks were infected, compared to the findings of earlier Norwegian and Scandinavian studies.
Migratory birds are thought to be an important factor in the global spreading of ticks and tick-borne pathogens. Some of Kjelland's work involved collecting ticks from migratory birds in order to study them. Ticks from 6538 migratory birds caught at Lista Ornithological Station were analysed to find out whether they were infected by Borrelia. Kjelland's study corroborates the assumption that birds play an important role in the spreading of ticks and that they may be partly responsible for the prevalence of various genotypes of B. burgdorferi s.l. in Europe.
The hare population seems to be in strong decline in Norway. The results of Kjelland's doctoral research indicate that a Borrelia infection spread from the bite to the bloodstream or internal organs seldom occurs in hares and that the bacterium probably does not play a significant role in the decline of the hare population. But Kjelland's findings show that hares can be reservoirs for certain genotypes of the bacterium.
The role played by deer in the ecology of Lyme borreliosis is a subject of debate. Kjelland's doctoral thesis indicates that there is a lower incidence of the Borrelia bacterium in ticks that have sucked blood from deer and moose than in ticks collected from the ground/vegetation.