Canine monocytic ehrlichiosis (CME) is a major tick-borne disease worldwide. Diagnosis of CME can be challenging, as the patients may present with variable, often non-specific, clinical signs associated with different stages of the infection, or co-infections. Ehrlichia canis is the etiological agent. Diagnosis of CME is generally supported by detection of E. canis antibodies either by indirect immunofluorescence assay (IFA) and/or ELISA. Several rapid point-of-care test kits are also available, but their relative accuracies have not been reported. The aim of this study was to evaluate the performance of three point-of-care test kits for detection of E. canis antibodies.

Three test kits evaluated included SNAP® 4Dx® Plus (IDEXX), Speed Duo Leish K/Ehrli^TM (BVT/Virbac), and FASTest® EHRLICHIA canis (MegaCor). Surplus samples were collected from IDEXX Reference Laboratories (IRL) at Ludwigsburg, Germany, and Phoenix, AZ, USA after requested diagnostic testing was completed. These were serum samples from suspected CME cases submitted by veterinarians for E. canis IFA and other testing. A total of 104 positive (IFA titre ≥1:400) and 163 IFA-negative samples were included in this study. Samples were blinded and randomized for testing with rapid tests. Each result was interpreted by 3 technicians. A test was considered positive when 2 or 3 technicians called it positive; negative when 2 or 3 technicians called it negative.

Compared to E. canis IFA, sensitivity/specificity was 95.2%/100% for SNAP, 84.6%/82.0% for Speed Duo and 82.2%/84.0% for FASTest, respectively.

The number of false-positive results was surprisingly high on Speed Duo and FASTest tests. To further confirm these results, all 163 IFA-negative samples were evaluated using a species-specific ELISA (McBride et al. 2007) and they all tested negative. Of these, 118 were sourced from dogs living in Germany, non-endemic for E. canis, yet 21 (17.8%) were tested positive by the Speed Duo test, and 16 (13.6%) positive by the FASTest test.

For E. canis, which has a reported prevalence rate of 1–5% in the U.S. and many European countries, tests with low specificity could have a very low positive predictive value. Consistent with previously published studies (Miró et al. 2013; Rene-Martellet et al. 2015), results from this study suggest that SNAP 4Dx Plus is an accurate point-of-care test useful for differential diagnosis or screening.

Disclosures

Disclosures to report
All authors are employees of IDEXX Laboratories, Inc.