Tularaemia can infect and be transmitted between a large number of animal species, including humans. For the first time Gete Hestvik shows, in a dissertation from the National Veterinary Institute (SVA) and Swedish University of Agricultural Sciences (SLU), that the causative bacteria, Francisella tularensis, in Sweden also can be found in the muscle of hares and that antibodies against the bacterium can be detected in brown bear, red fox, wild boar and wolverine.
Tularaemia is one of the most common zoonotic diseases diagnosed in humans in Sweden, and it is also present in most European countries. Differences in surveillance and reporting of the disease, together with different ecosystems, the variation of arthropod vectors (e.g. ticks and mosquitos), small rodent species and other wildlife species make direct comparisons across all of Europe difficult.
“A complex disease”
– Tularaemia is a complex disease that involves a large number of animal hosts, as well as ticks and mosquitos and the surrounding environment, says PhD-candidate Gete Hestvik.
Mountain hares and several small rodent species develop acute disease that quickly leads to death. In contrast, many predators and scavengers, such as brown bear, wolverine, red fox and wild boar, develop mild or no disease. Common symptoms in humans include fever, headache and nausea.
“Under-cooked hare meat a risk”
– My study shows that tularaemia causes similar lesions in Swedish European brown hares, mountain hares and the two yellow-necked mice investigated. The disease has a rapid course and spreads to many organs, quickly leading to death. The finding of bacteria in the muscle of hares shows that humans eating under-cooked hare meat are at risk of infection.
– In addition, some of the European brown hares investigated had chronic changes in lungs and/or kidneys. This shows that they were sick for a longer period of time, and that they might be potential reservoirs for F. tularensis in Sweden, as has been described in other parts of Europe, says Gete Hestvik.
Investigations of predators and scavengers detected antibodies against F. tularensis in brown bear, red fox, wild boar and wolverine. Measurement of antibodies in these species may be useful for disease surveillance in the future to investigate how the disease varies over time and to detect spread to new areas.