Tularaemia in Swedish wildlife

Tularaemia is a zoonotic disease caused by the bacterium Francisella tularensis, which may infect a wide range of hosts. The subspecies known to cause disease in Europe is F. tularensis subsp. holarctica. The susceptibility to develop disease varies between animal species. For example, mountain hares (Lepus timidus) and many small rodent species succumb to fulminate disease, while many carnivores and omnivores show no signs of clinical disease. This thesis has investigated the pathology and serology of tularemia in selected wildlife hosts. It has also reviewed the status of tularaemia in Europe in a One-Health perspective. Tularaemia is widely distributed throughout Europe. Differences in surveillance and reporting between countries, different ecosystems, the presence of different species of arthropod vectors and wildlife species, present difficulties in making direct comparisons across all of Europe. The pathology of tularaemia in European brown hares (Lepus europaeus), mountain hares and two yellow-necked mice (Apodemus flavicollis) were similar, all presenting with acute disseminated disease. However, some of the European brown hares, in addition to the acute lesions, also had subacute or chronic changes. This raises the question of whether European brown hares in Sweden might play an epidemiological role as reservoir of F. tularensis. F. tularensis was also demonstrated in muscles of infected hares, which highlights the risk of acquiring infection through consumption of under-cooked meat. Many predators and omnivores develop antibodies upon infection and therefore may be suitable sentinels of the presence of tularaemia. The study revealed seropositivity in brown bear, red fox, wild boar and wolverine, for the first time reported in Sweden. This thesis contributes to the knowledge of tularaemia in Europe, its pathology in European brown hares and yellow-necked mice, and its possible routes of infection and shedding. Additionally, it contributes to the understanding of the role of predators and scavengers. The results of our studies highlight the importance of further investigations of different wildlife species to explore their role in the epidemiology of tularaemia, as possible sources of infection, transmitters of disease and potential reservoirs