Detection of tularemia in European brown hares (Lepus europaeus) and humans reveals endemic and seasonal occurrence in Baden-Wuerttemberg, Germany

Tularemia is a highly contagious infectious disease which has re-emerged in Germany with varying spatial and temporal distribution. European brown hares (Lepus europaeus) and wild rabbits (Oryctolagus cuniculus) typically serve as hosts for the zoonotic pathogen Francisella tularensis subsp. holarctica, but many animals including insects and ticks can represent relevant vectors for tularemia. Since the beginning of 2016, cases of tularemia have seemed to accumulate within the brown hare population in Baden-Wuerttemberg (BW). Simultaneously, the number of human infections has also risen compared to previous years. Natural emergence or re-emergence of tularemia can appear in susceptible populations at any time. Knowledge about the actual occurrence and spreading of tularemia is essential to inform health professionals and risk groups, such as hunters, forest workers and farmers in endemic areas. Therefore, we assessed the spatial and temporal distribution of tularemia in brown hares and wild rabbits in BW, retrospectively based on results obtained from cultural and molecular investigations during routine diagnosis, including 179 brown hares (55 positive animals) and ten wild rabbits (0 positive animals), which were randomly found moribund or dead between January 2010 and June 2016, In addition we assessed surveillance data from notified human cases during the same time period. Our data suggest that tularemia is endemic in BW due to an annual and widespread occurrence. Furthermore, tularemia occurs with seasonal peaks in spring and autumn, in particular in October. There are counties where tularemia was observed in both humans and brown hares; however, there are regions with no coincidence of cases in humans and brown hares, suggesting that other reservoirs such as insects or ticks may play a relevant role as vectors. The results of the present study suggest that tularemia is an endemic zoonosis in BW which poses a permanent infection risk to humans.