Human pathogens associated with the blacklegged tick Ixodes scapularis: a systematic review.

Ye Li,Stephen Moore,Steven Johnson,Beate Sander,Doug Sider,Samir N. Patel,Curtis B. Russell,Mark P. Nelder,Nina Jain Sheehan

doi:10.1186/s13071-016-1529-y

Abstract

BackgroundThe blacklegged tick Ixodes scapularis transmits Borrelia burgdorferi (sensu stricto) in eastern North America; however, the agent of Lyme disease is not the sole pathogen harbored by the blacklegged tick. The blacklegged tick is expanding its range into areas of southern Canada such as Ontario, an area where exposure to blacklegged tick bites and tick-borne pathogens is increasing. We performed a systematic review to evaluate the public health risks posed by expanding blacklegged tick populations and their associated pathogens.MethodsWe followed PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines for conducting our systematic review. We searched Ovid MEDLINE, Embase, BIOSIS, Scopus and Environment Complete databases for studies published from 2000 through 2015, using subject headings and keywords that included “Ixodes scapularis”, “Rickettsia”, “Borrelia”, “Anaplasma”, “Babesia” and “pathogen.” Two reviewers screened titles and abstracts against eligibility criteria (i.e. studies that included field-collected blacklegged ticks and studies that did not focus solely on B. burgdorferi) and performed quality assessments on eligible studies.ResultsSeventy-eight studies were included in the final review, 72 were from the US and eight were from Canada (two studies included blacklegged ticks from both countries). Sixty-four (82 %) studies met ≥ 75 % of the quality assessment criteria. Blacklegged ticks harbored 91 distinct taxa, 16 of these are tick-transmitted human pathogens, including species of Anaplasma, Babesia, Bartonella, Borrelia, Ehrlichia, Rickettsia, Theileria and Flavivirus. Organism richness was highest in the Northeast (Connecticut, New York) and Upper Midwest US (Wisconsin); however, organism richness was dependent on sampling effort. The primary tick-borne pathogens of public health concern in Ontario, due to the geographic proximity or historical detection in Ontario, are Anaplasma phagocytophilum, Babesia microti, B. burgdorferi, Borrelia miyamotoi, deer tick virus and Ehrlichia muris-like sp. Aside from B. burgdorferi and to a much lesser concern A. phagocytophilum, these pathogens are not immediate concerns to public health in Ontario; rather they represent future threats as the distribution of vectors and pathogens continue to proliferate.ConclusionsOur review is the first systematic assessment of the literature on the human pathogens associated with the blacklegged tick. As Lyme disease awareness continues to increase, it is an opportune time to document the full spectrum of human pathogens transmittable by blacklegged ticks.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1529-y) contains supplementary material, which is available to authorized users.

Highlights

The blacklegged tick Ixodes scapularis transmits Borrelia burgdorferi in eastern North America; the agent of Lyme disease is not the sole pathogen harbored by the blacklegged tick
The blacklegged tick Ixodes scapularis is the vector of Borrelia burgdorferi in eastern North America
To determine what tick-borne diseases are reportable to public health officials, we reviewed reportable disease lists for Anaplasma, Babesia, Bartonella, Borrelia, deer tick virus (DTV), Ehrlichia and Rickettsia in Canada (Manitoba, Ontario and Quebec) and the US (Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania and Wisconsin) (Table 2)

Summary

Introduction

The blacklegged tick Ixodes scapularis transmits Borrelia burgdorferi (sensu stricto) in eastern North America; the agent of Lyme disease is not the sole pathogen harbored by the blacklegged tick. The blacklegged tick Ixodes scapularis is the vector of Borrelia burgdorferi (sensu stricto) (agent of Lyme disease) in eastern North America. In Ontario, this range expansion has not been uniform; spreading primarily into suburban and rural areas with mixed deciduous forests, where vertebrate hosts are abundant and local climate is favourable to blacklegged tick survival [4]. Blacklegged ticks were soon implicated as vectors of Anaplasma phagocytophilum (anaplasmosis), and more recently, Borrelia miyamotoi (B. miyamotoi disease) and deer tick virus (DTV; DTV encephalitis) [8,9,10]. Uncommon in Ontario’s blacklegged ticks, so far, these pathogens are likely to become more prevalent in the future, as has been the case in recently-invaded jurisdictions such as Maine [11]

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