Endemicity of Anaplasma phagocytophilum (previously Ehrlichia spp.) and Babesia microti in Wisconsin, USA: benchmark results following introduction of molecular diagnostic methods for routine patient management (2012-2013)

ECCMID Spain, May 10-13th, 2014

Fritsche T.R.; Marti T.N.; Schotthoefer A.M.; Uphoff T.S

OBJECTIVES: To establish benchmark prevalence rates of tick-borne diseases (Anaplasma phagocytophilum, Ehrlichia spp., and Babesia microti) post-introduction of nucleic acid amplification assays in an endemic region of the upper Midwestern USA. Expanding distribution of the tick vectors Ixodes scapularis and, to a lesser extent, Amblyomma americanum, is driving an increased recognition of tick-borne diseases within the area. Here we describe the routine application of molecular methods for the diagnosis of anaplasmosis, ehrlichiosis, and babesiosis in a regional healthcare system, and present benchmark results for 2012-2013.

METHODS: Clinical specimens (EDTA blood, n=10,261) submitted for testing as part of routine management of patients presenting with history and/or symptoms compatible with a tick-borne illness included 5,463 and 4,798 requests, respectively, for Anaplasma/Ehrlichia spp. (date range 12/2012-10/2013) and B. microti (05/2013-10/2013). Tests included two real-time PCR assays, one targeting the groEL operon with melt-curve analysis for differentiation of A. phagocytophilum, E. chaffeensis, E.ewingii, and a novel pathogen identified tentatively as Ehrlichia sp. Wisconsin (Pritt, N Engl J Med 365:422, 2011; Schotthoefer, J Clin Microbiol 51:2147, 2013), and another targeting a variable region of the B. microti 18s rRNA gene (Teal, J Clin Microbiol 50:903, 2012). Performance characteristics for both assays were determined previously.

RESULTS: Overall, 247 (2.4%) of performed tests were positive and included 209 (3.8%) A. phagocytophilum; 4 (0.07%) Ehrlichia sp. Wisconsin (= Ehrlichia muris-like agent); 2 (0.04%) E. chaffeensis; and 32 (0.67%) B. microti. These results may be a more accurate estimation of cases detected within our healthcare system given that other routinely requested laboratory tests (blood smear analysis, serology) are known to be less sensitive and/or specific than nucleic acid tests. These results confirm the expanding range of the rarer Ehrlichia spp. in our state as well as the endemic nature of A. phagocytophilum and B. microti in the upper Midwestern USA.

CONCLUSION: Tick-borne infections in Wisconsin detected by real-time PCR methods during 2012-2013 included A. phagocytophilum, Ehrlichia sp. Wisconsin, E. chaffeensis and B. microti. While prevalence rates are low (2.4% in aggregate), presence of these species along with recently described geographic spread of competent tick vectors creates a worrisome public health threat superseded only by Lyme disease, also known to be both endemic and enzootic in our region.