Francisella tularensis Cluster in Europe | CDC EID

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Volume 15, Number 12–December 2009
Dispatch
Identification of Francisella tularensis Cluster in Central and Western Europe
Paola Pilo,1 Anders Johansson,1 and Joachim Frey
Author affiliations: University of Bern, Bern, Switzerland (P. Pilo, J. Frey); Umeå University, Umeå, Sweden (A. Johansson); and Swedish Defence Research Agency, Umeå (A. Johansson)

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Abstract
We conducted a molecular analysis of Francisella tularensis strains isolated in Switzerland and identified a specific subpopulation belonging to a cluster of F. tularensis subsp. holarctica that is widely dispersed in central and western continental Europe. This subpopulation was present before the tularemia epidemics on the Iberian Peninsula.

Tularemia is a classical zoonosis caused by the facultative intracellular bacterium Francisella tularensis; it is transmissible to humans at infectious doses as low as 10–50 bacteria when inhaled in aerosols or by inoculation of the skin. Traditionally, tularemia is thought of as a disease contracted by persons performing outdoor activities such as hunting or farming, but it can also be acquired from pets, for example, hamsters or prairie dogs, which are occasionally traded internationally (1). During the past 15 years, the reemergence of tularemia has been reported in several European countries (2–4). Spain is a notable example, reporting 916 human infections from 1997 through 2007 in the Castilla and León regions alone (5). However, tularemia is rarely diagnosed in central Europe. In Switzerland, F. tularensis infection was first described in the 1950s, but the pathogen was not isolated until 1996, when F. tularensis infection began to reappear sporadically. To better understand the genetic diversity of Swiss F. tularensis strains and their relationship to strains from other geographic areas, we analyzed strains from Switzerland by using several methods that had been previously demonstrated to resolve genetic differences between F. tularensis subsp. holarctica strains: multilocus tandem repeat analysis (MLVA), canonical F. tularensis insertion deletion element (Ftind) analysis, and region of difference (RD) 23 analysis (3,6,7).

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