Lone Star Ticks Aren't Transmitting Lyme Disease Borrelia
Lone Star ticks (Amblyomma americanum) are the main human-biting ticks in southeastern and southcentral regions of the U.S., accounting for over 90% of reported tick bites in the south. While Lone Star ticks have long been considered incompetent to transmit Lyme-group Borrelia, that belief has been increasingly called into question following publication of reported detection of B. burgdorferi DNA in 2 A. americanum ticks removed from humans, and in humans bitten by A. americanum (Clark et al. 2013, Int J Med Sci).
In a study that appeared this week ahead of print in the Journal of Clinical Microbiology, Ellen Stromdahl and collaborators summarized results from testing over 22,500 Lone Star ticks removed from Department of Defense personnel and dependents between 1997-2010 for Lyme group Borrelia through the DOD Human Tick Test Kit program. Over the same time period, more than 5,400 blacklegged ticks (Ixodes scapularis) were tested similarly. As part of this study, they also tested >1,000 Lone Star ticks removed from humans using the same PCR primers and thermocycling protocol as in the Clark et al. study. While 24.7% of the blacklegged ticks tested positive for Lyme group Borrelia DNA, the study authors found NO measurable prevalence of B. burgdorferi in Lone Stars using any of the testing protocols. A careful study of the Clark et al. assay revealed potential methodological flaws that were responsible for “indistinct and inconsistent results;” most likely, the authors suggest, is the Clark et al. assay for Lyme-group Borrelia occasionally detects non-Lyme group B. lonestari non-specifically. These important findings provide the strongest evidence to date that Lone Star ticks are NOT transmitting Lyme group Borrelia infections to humans.