Re-emergence of tularemia in Germany: presence of Francisella tularensis in different rodent species in endemic areas

Abstract

Background: Tularemia re-emerged in Germany starting in 2004 (with 39 human cases from 2004 to 2007) after over 40 years of only sporadic human infections. The reasons for this rise in case numbers are unknown as is the possible reservoir of the etiologic agent Francisella (F.) tularensis. No systematic study on the reservoir situation of F. tularensis has been published for Germany so far.

Methods: We investigated three areas six to ten months after the initial tularemia outbreaks for the presence of F. tularensis among small mammals, ticks/fleas and water. The investigations consisted of animal live-trapping, serologic testing, screening by real-time-PCR and cultivation.

Results: A total of 386 small mammals were trapped. F. tularensis was detected in five different rodent species with carrier rates of 2.04, 6.94 and 10.87% per trapping area. None of the ticks or fleas (n = 432) tested positive for F. tularensis. We were able to demonstrate F. tularensis-specific DNA in one of 28 water samples taken in one of the outbreak areas.

Conclusion: The findings of our study stress the need for long-term surveillance of natural foci in order to get a better understanding of the reasons for the temporal and spatial patterns of tularemia in Germany.

Figure 1

Study sites, Germany, 2004–2006. Green dots indicate the investigation areas, red dots the three largest German cities for orientation. The number of small mammals caught and the F. tularensis detection rate are shown in parenthesis.

Figure 2

Distribution of rodent trapping areas (marked in green) and water sample collection sites (red dots) in an exemplary area (DA). The large red dot indicates the water sample tested positive for F. tularensis.