H 4 Detection and Genetic Characterization of Granulocytic Ehrlichiae from Ixodes scapularis Ticks Collected in Canada

L.R.LINDSAY, M.DREBOT*, A. DIBERNARDO, H.ARTSOB, T.GALLOWAY.  Zoonotic Diseases and Special Pathogens, National Microbiology Laboratory, PPHB, Health Canada, Winnipeg, MB. Department of Entomology, University of Manitoba, Winnipeg, MB.  

Objective: As part of on-going studies on the occurrence of tick-borne pathogens in Canada, DNA extracts from blacklegged ticks, Ixodes scapularis, collected by passive surveillance, were tested for the presence of human granulocytic ehrlichiosis (HGE) agent genome.

Methods: DNA was extracted from individual blacklegged ticks and added to PCR reaction mixtures containing primers specific for the HGE-agent 16S rRNA gene. The resulting rRNA amplicons were sequenced to verify the presence of tick associated (GE) granulocytic ehrlichiae. To further genotype GE strains, portions of the pathogen's Ank gene were amplified, sequenced, and characterized by phylogenetic procedures.

Results: A total of 576 blacklegged ticks were screened for the HGE-agent using PCR amplification of the 16S rRNA gene. HGE-agent genome was detected in ticks collected in Manitoba (5/203; 2.5%), Quebec (1/259; 0.4%), and Prince Edward Island (1/42; 2.4%). Phylogenetic analysis of GE Ank gene sequences showed that the majority of HGE-like agents from Manitoba exhibited high sequence identity with GE from Wisconsin and Minnesota. In contrast, HGE-like agents associated with I. scapularis in eastern Canada were genetically distinct from Manitoba GE and were part of a genetic clade comprising GE from ticks collected in Northeastern United States.

Conclusion: Though the prevalence of HGE-like pathogens in blacklegged ticks collected in Canada was much lower than those reported in tick-endemic localities in the US, Canadians clearly have a definable but low risk of exposure to this pathogen. Physicians should consider HGE as part of their differential diagnosis in patients who present with appropriate clinical symptoms.