Jaenson et al.
The importance of wildlife in the ecology and epidemiology of the TBE virus in Sweden: incidence of human TBE correlates with abundance of deer and hares.
Parasit. Vectors 2018; 11: 477, doi.org/10.1186/s13071-018-3057-4
The epidemiology of TBE is complex and depends amongst others on the climate, density of ticks, tick maintenance hosts and transmission hosts. The density of nymphs infected with the TBE virus in a habitat is a major factor for the risk that people become infected. In Sweden, the number of TBE cases has increased during the last forty years and it is assumed that one reason for this trend is the increase of density and distribution of the virus’ vector Ixodes ricinus and this may be linked with the increasing number of cervids like deer or other potential maintenance hosts. The authors have analyzed the density of various wildlife animals in Sweden for the period from 1960 to 2012 (based on hunting statistics) – roe deer, red deer, fallow deer, elk, wild boar, mountain and European hare – which are thought to act as maintenance hosts – and also their predators – the red fox and the lynx. The authors found that there was a positive covariance for the number of red and roe deer, and mountain hare with the incidence of TBE cases and a negative covariance for elk and fallow deer and no covariance for the boar, lynx and fox. The authors discuss their findings in great detail and conclude that the availability of deer to transport ticks over large areas may have contributed to the increased density and range of ticks creating new foci of TBE virus.