Abstract
The causative agent of tularemia, Francisella tularensis, is a formidable biologic agent that occurs naturally throughout North America. We examined genetic and spatial diversity patterns among 161 US F. tularensis isolates by using a 24-marker multiple-locus variable-number tandem repeat analysis (MLVA) system. MLVA identified 126 unique genotypes. Phylogenetic analyses showed patterns similar to recently reported global-scale analyses. We observed clustering by subspecies, low genetic diversity within F. tularensis subsp. holarctica, and division of F. tularensis subsp. tularensis into 2 distinct subpopulations: A.I. and A.II. The 2 F. tularensis subsp. tularensis subpopulations also represent geographically distinct groups; A.I. occurs primarily in the central United States, and A.II. occurs primarily in the western United States. These spatial distributions are correlated with geographic ranges of particular vectors, hosts of tularemia, and abiotic factors. These correlates provide testable hypotheses regarding ecologic factors associated with maintaining tularemia foci.
Highlights
The causative agent of tularemia, Francisella tularensis, is a formidable biologic agent that occurs naturally throughout North America
In an attempt to identify factors that may influence the maintenance of endemic tularemia foci in the United States, we examined correlations between observed genetic groupings that were identified by using multiple-locus variable-number tandem repeat analysis (MLVA) and biotic and abiotic variables
With the exception of the 1920 Utah type strain (Utah 112) and 1 isolate from California, the other 4 F. tularensis subsp. novicida isolates were collected in southeastern states (Figures 4 and 6)
Summary
The causative agent of tularemia, Francisella tularensis, is a formidable biologic agent that occurs naturally throughout North America. Tularensis subpopulations represent geographically distinct groups; A.I. occurs primarily in the central United States, and A.II. Occurs primarily in the western United States These spatial distributions are correlated with geographic ranges of particular vectors, hosts of tularemia, and abiotic factors. Known as rabbit fever or deer-fly fever, is caused by the gram-negative intracellular pathogen Francisella tularensis [1]. This bacterium was first identified in 1912 following reports of a plaguelike illness in ground squirrels in Tulare County, California [2]. Human tularemia incidence in the United States peaked in 1939 with 2,291 reported cases [5] and has since decreased to 100–200 cases annually [8]
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