Seroprevalence of Ehrlichia canis, Ehrlichia equi, and Ehrlichia risticii in sick dogs from North Carolina and Virginia

Ehrlichia canis, E equi, and E risticii seroprevalence was determined by mi croimmunofluorescent antibody testing (IFA) in a sequential population of 1 ,845 sick dogs admitted during a 1-year period to the North Carolina Stars University Veterinary Teaching Hospital. A seroreactor was defined by a rec iprocal IFA titer of greater than or equal to 80 to E canis, E equi, or E r isticii antigens. Of the 48 IFA seroreactors. 44 dogs were seroreactive to E canis, 21 to E equi, and 0 to E risticii. Seventeen dogs reacted to both E canis and E equi antigens. There was concordance of E canis IFA and weste rn immunoblot (WI) test results fur 36/44 dogs. Because of cross-reactivity of E canis sera with E equi antigens, WI was of less utility to confirm E equi exposure. After elimination of E canis seroreactors, there was concord ance of 2/4 E equi IFA and WI test results. Based upon a retrospective revi ew of medical records, ehrlichiosis was diagnosed in 10/48 (21%) IFA serore active dogs, 9 of which were confirmed positive by WI. Of the remaining 38 IFA seroreactors, 29 also were confirmed by E canis or E equi WI. These res ults indicate that (1) ehrlichiosis nor diagnosed in the majority of serolo gically confirmed cases, (2) based upon E canis and E equi WI analysis, IFA testing was not specific (21% false positive). (3) E canis sera cross-reac t with E equi antigens, and (4) serologic evidence of E risticii infection was lacking in the dog population studied.