Applying Whole-Genome Sequencing to Tularemia: Does Environment Trump Genes?

Summary and Comment |
November 18, 2014

Applying Whole-Genome Sequencing to Tularemia: Does Environment Trump Genes?

  1. Neil M. Ampel, MD

Analysis of 10 isolates from a tularemia outbreak in Sweden showed little relatedness between the isolates and temporal or spatial aspects of the outbreak.

  1. Neil M. Ampel, MD

Respiratory tularemia results from inhalation of aerosolized Francisella tularensis. This mode of transmission has led to concern about the use of this organism as an agent of bioterrorism; thus, the ability to detect tularemia outbreaks and identify their source is very important.

Between mid-July and late October, 2010, a large outbreak of tularemia occurred in a sparsely populated region of central Sweden. Seventy-eight cases were detected, of which 67 were respiratory. Analysis of dates of onset and likely geographic places of infection revealed a complex pattern suggesting multiples sources of infection. Both severe and nonsevere cases occurred within the same clusters.

F. tularensis isolated from 10 patients with severe respiratory tularemia were analyzed using whole-genome sequencing (WGS); the resulting sequences were compared with 110 archival reference genomic sequences from around the world. Several outbreak isolates were more closely related to archival isolates collected in distant geographic regions and in different years than to other current isolates. The overall outbreak pattern appeared to be an example of multiple disease clusters occurring in a single season.

Comment

WGS is a powerful tool that allows for a deep genetic analysis of microorganisms. In the case of a natural outbreak of tularemia in Sweden, WGS analysis of a small number of isolates did not demonstrate correlation of genetic difference with temporal or spatial aspects of the outbreak. This finding suggests that ecological and environmental factors that favor tularemia transmission may be playing an important role in natural outbreaks of the disease.

Editor Disclosures at Time of Publication

  • Disclosures for Neil M. Ampel, MD at time of publication Editorial boards Medical Mycology Leadership positions in professional societies Coccidiodomycosis Study Group (President-Elect)

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