Tularemia among Free-Ranging Mice without Infection of Exposed Humans, Switzerland, 2012

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Francesco C. Origgi, Barbara König, Anna K. Lindholm, Désirée Mayor, and Paola Pilo

Author affiliations: University of Bern, Bern, Switzerland (F.C. Origgi, D. Mayor, P. Pilo); and University of Zurich, Zurich, Switzerland (B. König, A.K. Lindholm)

Abstract

The animals primarily infected by Francisella tularensis are rapidly consumed by scavengers, hindering ecologic investigation of the bacterium. We describe a 2012 natural tularemia epizootic among house mice in Switzerland and the assessment of infection of exposed humans. The humans were not infected, but the epizootic coincided with increased reports of human cases in the area.

Although the house mouse (Mus musculus domesticus) is a common model for infection with Francisella tularensis (1), no recent and detailed data are available about natural tularemia outbreaks in this species. Tularemia mainly affects rodents and lagomorphs (2), but because these species are rapidly consumed by scavengers (3), it is challenging to conduct investigations of the biologic cycle of F. tularensis in the environment. Furthermore, the disease mostly occurs sporadically, although outbreaks have been reported in animals and humans (2). We describe a natural outbreak of tularemia among a population of free-ranging house mice; the epizootic occurred in Switzerland in 2012 and was associated with possible human exposure. The mouse study was approved by the Swiss Animal Experimentation Commission (Kantonales Veterinäramt Zürich; permit 51/2010).

Dr. Origgi, a veterinary pathologist and microbiologist, is responsible for the wildlife diagnostic service of the Centre for Fish and Wildlife Health at the University of Bern. His main interests are host–pathogen interactions and lower vertebrate pathology and immunology.

Acknowledgment

This study was supported by the Swiss Federal Office for the Environment (grant no. 12.0003.KP/L121-0964) and by the Swiss Expert Committee for Biosafety (grant no. 04.1240.PZ/L064-7521), and data collection was supported by the Swiss National Science Foundation (grant no. 310030M-138389).

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Figure

Figure. Monthly distribution of the number of carcasses of free-ranging house mice collected from a barn and the number positive for F. tularensis, Switzerland, May 2012–June 2013.

Table

Table. Estimated time 11 researchers spent in a barn inhabited by Francisella tularensis–infected house mice, Switzerland, June 1–August 31, 2012

Suggested citation for this article: Origgi FC, König B, Lindholm AK, Mayor D, Pilo P. Tularemia among free-ranging mice without infection of exposed humans, Switzerland, 2012. Emerg Infect Dis. 2015 Jan [date cited]. http://dx.doi.org/10.3201/eid2101.140906

DOI: 10.3201/eid2101.140906