Northern and southern blacklegged (deer) ticks are genetically distinct with different histories and Lyme spirochete infection rates

Guang Xu,Stephen M Rich,Ben Wielstra,Ben Wielstra

doi:10.1038/s41598-020-67259-0

Guang Xu, Stephen M Rich + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-67259-0

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Abstract

Lyme borreliosis (LB) is the archetypal emerging zoonosis and is dependent on transmission by ticks in the genus Ixodes. Understanding the origin, maintenance, and spread of these ticks contributes much to our understanding of the spread of LB and other disease agents borne by these ticks. We collected 1232 Ixodes scapularis ticks from 17 east coast sites ranging from New Hampshire to Florida and used mtDNA, three nuclear genetic loci, and incorporated Bayesian analyses to resolve geographically distinct tick populations and compare their demographic histories. A sparse, stable, and genetically diverse population of ticks in the Southeastern US, that is rarely infected with the agent of LB is genetically distinct from an abundant, expanding, and comparatively uniform population in the Northeast, where epidemic LB now constitutes the most important vector borne disease in the United States. The contrasting geography and demography of tick populations, interpreted in the context of the geological history of the region, suggests that during the last glacial period such ticks occupied distinct refugia, with only the northern-most site of refuge giving rise to those ticks and pathogens now fueling the epidemic.

Highlights

Lyme disease is the most commonly reported vector borne disease in North America though its risk varies widely by geographic region[1]
single nucleotide polymorphisms (SNPs) analysis for ten ticks showed that samples from New Jersey and Virginia formed a homogeneous group with low genetic diversity, whereas southern ticks from Georgia and Mississippi consisted of two separate groups, each with high genetic diversity
We found that northeastern and southeastern I. scapularis tick populations are genetically distinct with different histories and Lyme spirochete infection rates

Summary

Introduction

Lyme disease is the most commonly reported vector borne disease in North America though its risk varies widely by geographic region[1]. In the United States, most human Lyme disease cases are reported in the Northeast and upper Midwest, while cases in western and southern regions of the country are low[2]. This contrast is evident in the entomological record where the frequency of B. burgdorferi is 2–8% in the main vector I. scapularis adult ticks in the South[3,4], compared to infection rates averaging 50% in New England[5]. We found that northeastern (northern) and southeastern (southern) I. scapularis tick populations are genetically distinct with different histories and Lyme spirochete infection rates

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