Borrelia burgdorferi not confirmed in human-biting Amblyomma americanum ticks from the southeastern United States.

Stromdahl EY1, Nadolny RM2, Gibbons JA3, Auckland LD4, Vince MA5, Elkins CE5, Murphy MP5, Hickling GJ6, Eshoo MW7, Carolan HE7, Crowder CD7,Pilgard MA8, Hamer SA4.

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Abstract

The predominant human-biting tick throughout the southeastern United States is Amblyomma americanum. Its ability to transmit pathogens causing Lyme disease-like illnesses is a subject of ongoing controversy. Results of previous testing by the Department of Defense Human Tick Test Kit Program, and other laboratories, indicated that it is highly unlikely that A. americanum transmits any pathogen that causes Lyme disease. In contrast, a recent publication by Clark and colleagues (K.L. Clark, B. Leydet, S. Hartman, Int. J. Med. Sci. 10:915-931, 2013) reported detection of Lyme group Borrelia in A. americanum using a nested flagellin gene PCR. We evaluated this assay and by using it, and other assays, to test 1,097 A. americanum collected from humans. Using the Clark assay, in most samples we observed non-specific amplification, and non-repeatability of results on subsequent testing of samples. Lack of reaction specificity and repeatability is consistent with mispriming, likely due to high primer concentrations and low annealing temperatures in this protocol. In six suspect-positive samples, Borrelia lonestari was identified by sequencing of an independent gene region; this is not a Lyme-group spirochete and is not considered zoonotic. B. burgdorferi was weakly amplified from one pool using some assays, but not others, and attempts to sequence the amplicon of this pool failed, as did attempts to amplify and sequence B. burgdorferi from the five individual samples comprising this pool. Therefore, B. burgdorferi was not confirmed in any sample. Our results do not support the hypothesis that A. americanum ticks vector Lyme group Borrelia infections.