SEAFWA 2018

AUTHORS: Graham Hickling, Janetta Kelly – University of Tennessee Institute of Agriculture

ABSTRACT: Lyme disease is caused by the bacterium Borrelia burgdorferi (Bb), which in the eastern US is vectored by the black-legged tick Ixodes scapularis. In southeastern states, black-legged ticks are widespread in many wooded habitats but are rarely infected with Bb; consequently, most human cases of Lyme disease originate from the Northeast and Upper Midwest. To explain this geographic pattern, it has been hypothesized that: i) tick abundance is too low in most southern states for Bb cycles to persist; and/or ii) immature black-legged ticks in the Southeast feed primarily on lizards, which are non-reservoir-competent hosts for Bb. The past decade, however, has seen emergence of Bb-infected tick populations in southwestern Virginia, southeastern Kentucky, and most recently eastern Tennessee. These emerging disease foci are closely associated with major river systems that may be acting as corridors for wildlife-mediated spread of northern strains of Bb, and northern genotypes of ticks. Tick genotype is key to assessing Lyme disease risk, because ‘northern’ I. scapularis have behavioral characteristics that increase the likelihood that they will attach to humans and transmit infection. The prospects for Lyme disease becoming more widespread in southern states in coming years will be discussed.