Prevalence of Ehrlichia muris in Wisconsin Deer Ticks Collected During the Mid 1990s

Abstract

Human ehrlichiosis is due to infection by tick transmitted bacteria of the genus Ehrlichia. Based on a hypothesis for the biogeography of deer tick transmitted infections, we undertook a focused search for the Eurasian E. muris in North American deer ticks. The search was stimulated by anecdotal reports of E. muris-like infection in human ehrlichiosis patients from Wisconsin. We analyzed archived adult deer ticks collected in northern Wisconsin during the 1990s by specific polymerase chain reaction for evidence of infection, and sequenced amplification products to identify E. muris. About 1% of 760 adult deer ticks collected from Spooner, Wisconsin in the 1990s contained E. muris DNA. We conclude that E. muris was present in North American deer ticks a decade ago and is likely to infect this human biting vector elsewhere in the U.S. Biogeographic theory and molecular phylogenetic methods can facilitate a targeted search for potential zoonoses.

Keywords: Ehrlichia muris; Ehrlichiosis; Ixodes dammini; PCR.; Wisconsin; deer ticks.

Fig. (1)

Phylogenetic analysis of Ehrlichia sp. DNA amplified from archived adult deer ticks collected in Spooner, Wisconsin during 1992-1997. DNA sequences of other Ehrlichia spp. were downloaded from NCBI Genbank, aligned using ClustalW, and then adjusted by eye using GeneDoc. MEGA was used to generate neighbor-joining trees for citrate synthase (left panel) and groesl (right panel) sequences using the Kimura 2-parameter model. 500 bootstrap replicates were done to assess the stability of the resulting branch nodes.