Dataset Information

Genotypic diversity of Francisella tularensis infecting Dermacentor variabilis ticks on Martha's Vineyard, Massachusetts.

ABSTRACT: Martha's Vineyard, Mass., has been the site of two outbreaks of tularemia (1978 and 2000). Although most patients from both outbreaks presented with pneumonic disease and although aerosol transmission has been suggested, the bite of a dog tick and exposure to rabbits remain the only proven modes of transmission. The factors that precipitated the tularemia outbreaks or the proximal determinants of human risk remain undescribed. We sought to test the hypothesis that the ongoing outbreak is due to a recent introduction event as opposed to amplification of a cryptic enzootic cycle. From 2001-2003, we collected 4,246 dog ticks and tested them in pools for evidence of tularemia by PCR. We then measured the genetic diversity of Francisella tularensis by using multiple-locus variable-number tandem repeat analysis. The prevalence of F. tularensis in dog ticks averaged 0.7%. From 29 positive pools, we identified 10 unique genotypes, which was an unexpectedly large degree of diversity (Simpson's index = 0.86). This degree of genetic diversity is inconsistent with a recent introduction event. We conclude that there has been long-standing enzootic transmission of tularemia on the island.

SUBMITTER: Goethert HK

PROVIDER: S-EPMC525218 | biostudies-literature | 2004 Nov

REPOSITORIES: biostudies-literature

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Genotypic diversity of Francisella tularensis infecting Dermacentor variabilis ticks on Martha's Vineyard, Massachusetts.

Goethert Heidi K HK Shani Inbar I Telford Sam R SR

Journal of clinical microbiology 20041101 11

Martha's Vineyard, Mass., has been the site of two outbreaks of tularemia (1978 and 2000). Although most patients from both outbreaks presented with pneumonic disease and although aerosol transmission has been suggested, the bite of a dog tick and exposure to rabbits remain the only proven modes of transmission. The factors that precipitated the tularemia outbreaks or the proximal determinants of human risk remain undescribed. We sought to test the hypothesis that the ongoing outbreak is due to ...[more]

PMID: 15528681

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Project description:BACKGROUND:The American dog tick, Dermacentor variabilis, is an important vector of pathogens to humans, wildlife and domestic animals in North America. Although this tick species is widely distributed in the USA and Canada, knowledge of its range-wide phylogeographic patterns remains incomplete. METHODS:We carried out a phylogenetic analysis of D. variabilis using samples collected from 26 USA states and five Canadian provinces. Tick samples (n = 1053 in total) originated from two main sources: existing archives (2000-2011), and new collections made from 2012 to 2013. We sequenced a 691 bp fragment of the cox1 gene from a subset (n = 332) of geographically diverse D. variabilis. DNA extracted from individual ticks (n = 1053) was also screened for a Francisella-like endosymbiont, using a targeted 16S rRNA sequencing approach, and important pathogens (Rickettsia spp. and Coxiella burnetii), using species-specific quantitative PCR assays. RESULTS:Maximum parsimony analysis of cox1 sequences revealed two major groups within D. variabilis with distinct geographical distributions: one from the eastern USA/Canada (Group 1) and one from the west coast states of the USA (California and Washington; Group 2). However, genetic subdivisions within both of these two major groups were weak to moderate and not tightly correlated with geography. We found molecular signatures consistent with Francisella-like endosymbionts in 257 of the DNA extracts from the 1053 individual ticks, as well as Rickettsia spp. and Coxiella burnetii in a small number of ticks (n = 29 and 2, respectively). Phylogenetic patterns for Francisella-like endosymbionts, constructed using sequence data from the bacterial 16S rRNA locus, were similar to those for D. variabilis, with two major groups that had a nearly perfect one-to-one correlation with the two major groups within D. variabilis. CONCLUSIONS:Our findings reveal a distinct phylogenetic split between the two major D. variabilis populations. However, high levels of genetic mixture among widely separated geographical localities occur within each of these two major groups. Furthermore, our phylogenetic analyses provide evidence of long-term tick-symbiont co-evolution. This work has implications for understanding the dispersal and evolutionary ecology of D. variabilis and associated vector-borne diseases.

Dataset Information

Genotypic diversity of Francisella tularensis infecting Dermacentor variabilis ticks on Martha's Vineyard, Massachusetts.

Publications

Genotypic diversity of Francisella tularensis infecting Dermacentor variabilis ticks on Martha's Vineyard, Massachusetts.

Similar Datasets

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