Tularemia in Alaska, 1938 - 2010

Abstract

Tularemia is a serious, potentially life threatening zoonotic disease. The causative agent, Francisella tularensis, is ubiquitous in the Northern hemisphere, including Alaska, where it was first isolated from a rabbit tick (Haemophysalis leporis-palustris) in 1938. Since then, F. tularensis has been isolated from wildlife and humans throughout the state. Serologic surveys have found measurable antibodies with prevalence ranging from < 1% to 50% and 4% to 18% for selected populations of wildlife species and humans, respectively. We reviewed and summarized known literature on tularemia surveillance in Alaska and summarized the epidemiological information on human cases reported to public health officials. Additionally, available F. tularensis isolates from Alaska were analyzed using canonical SNPs and a multi-locus variable-number tandem repeats (VNTR) analysis (MLVA) system. The results show that both F. t. tularensis and F. t. holarctica are present in Alaska and that subtype A.I, the most virulent type, is responsible for most recently reported human clinical cases in the state.

Figure 1

Number of human tularemia cases in Alaska reporting animal exposure.

Figure 2

Neighbor-joining dendrogram of Alaskan and 34 additional subclade A.I.Br.001/002 F. tularensis isolates based upon MLVA data. The dendrogram was generated using neighbor-joining analysis of mean character differences using PAUP 4.0b10 (D. Swofford, Sinauer Associates, Inc., Sunderland, MA). Bootstrap values ≥50, also generated using PAUP 4.0b10, are indicated and were based upon 1,000 simulations.