Characterization Of An Ehrlichia Muris-Like Organism Isolated From A Tick In Minnesota

Abstract

The Ehrlichia muris-like agent (EMLA) is a newly recognized zoonotic disease agent occurring in the Upper Midwestern United States. In the fall of 2011, two years after the organism was isolated from a human patient, a second isolate was cultured from an engorged tick. The following thesis is a description of the steps taken to identify this tick-derived organism as a second EMLA isolate. The tick-derived isolate (EmCRT) was characterized with a variety of techniques, including cell culture, genetic sequencing, tick-host transmission models, rodent histopathology, and transmission electron microscopy. Prior to this work, infection in ticks had not been well-described for most members of the Anaplasmataceae family, including Ehrlichia spp. The EmCRT isolate was transformed with a Himar1 transposon to produce mutant organisms that are visible under live microscopy in both cell culture and live tick tissues. In situ hybridization and transmission electron microscopy of whole-sectioned infected ticks enabled additional localization and description of tick tissues harboring EMLA. White-footed mice, as both a common host for immature ticks in the Upper Midwest, and the only non-human vertebrate species with evidence of EMLA infection, are a presumed reservoir host for this pathogen. To evaluate this, a tick-host transmission study was conducted, and we present evidence that white-footed mice are, indeed, competent reservoirs of EMLA. Co-feeding transmission between ticks was also demonstrated. Tick-transmitted EMLA was highly pathogenic for non-inbred rodents, emphasizing the importance of tick phenology and co-feeding transmission in the natural maintenance of EMLA.