Increasing Prevalence of Borrelia Burgdorferi Sensu Stricto–Infected Blacklegged Ticks in Tennessee Valley, Tennessee, USA

Graham J. Hickling; Janetta R. Kelly; Lisa D. Auckland; Sarah A. Hamer


Emerging Infectious Diseases. 2018;24(9):1713-1716. 

In This Article

Abstract and Introduction


In 2017, we surveyed forests in the upper Tennessee Valley, Tennessee, USA. We found Ixodes scapularis ticks established in 23 of 26 counties, 4 of which had Borrelia burgdorferi sensu stricto–infected ticks. Public health officials should be vigilant for increasing Lyme disease incidence in this region.


In the United States, Lyme disease caused by tickborne bacterium Borrelia burgdorferi sensu stricto occurs primarily in the Northeast and upper Midwest.[1] In eastern Tennessee, which is considered nonendemic for Lyme disease, most of the human population resides in a low-elevation swath of the Tennessee Valley bordered to the west by the Cumberland Plateau and the east by the Great Smoky Mountains. The vector of Lyme disease, the blacklegged tick Ixodes scapularis, was unreported in this area before 2006; in this year, uninfected adult ticks were collected from hunter-harvested deer in 8 Tennessee Valley counties (Figure 1, panel A).[2] This finding, plus uninfected I. scapularis ticks detected in Knox County in 2013, were later incorporated into the national distribution map for I. scapularis ticks.[3]

Figure 1.

County-level distribution of Ixodes scapularis ticks and Borrelia burgdorferi–infected I. scapularis ticks in upper Tennessee Valley, USA, 2006 and 2017. A county was classified as having an established I. scapularis population if ≥6 I. scapularis adult ticks or ticks of 2 life stages were collected in that county. A county was classified as having I. scapularis ticks reported if 1–5 I. scapularis ticks of a single life stage were collected in that county. A county was classified as infected if I. scapularis ticks infected with B. burgdorferi were detected in that county. A) I. scapularis ticks in 2006 (2), determined by collecting ticks from hunter-harvested deer. B) I. scapularis ticks in 2017 determined by drag-cloth surveying during the peak of adult tick activity (late October–January).

During 2000–2014, human Lyme disease cases expanded southward along the eastern foothills of the Appalachian Mountains in nearby Virginia.[4] In the winters of 2012 and 2013, B. burgdorferi–infected adult I. scapularis ticks were detected in Pulaski County, Virginia.[5] This report of abundant infected I. scapularis ticks only 100 km from the Tennessee border motivated us to investigate whether Borrelia-infected ticks might now be present in the Tennessee Valley.