Veterinary Parasitology 95 (2001) 1–15 Review Significance of serological testing for ehrlichial diseases in dogs with special emphasis on the diagnosis of canine monocytic ehrlichiosis caused by Ehrlichia canis Trevor Waner a,* , Shimon Harrus b , Frans Jongejan c , Hylton Bark b , Avi Keysary a , Albert W.C.A. Cornelissen c a Israel Institute for Biological Research, P.O. Box 19, Ness Ziona 70400, Israel b Koret School of Veterinary Medicine, Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel c Department of Parasitology and Tropical Veterinary Medicine, University of Utrecht, Utrecht, Netherlands Received 20 March 2000; received in revised form 11 July 2000; accepted 11 September 2000 Abstract Dogs are susceptible to a number of ehrlichial diseases. Among them, canine monocytic ehrli- chiosis is an important and potentially fatal disease of dogs caused by the rickettsia Ehrlichia canis. Diagnosis of the disease relies heavily on the detection of antibodies and is usually carried out using the indirect immunofluoresence antibody (IFA) test. The IFA test may be confounded by cross-reactivities between a number of the canine ehrlichial pathogens. This article presents a review of the ehrlichial diseases affecting dogs with reference to their immune responses, host specificities, cross-reactivites and diagnosis. Diagnostic means such as Western immunblot, dot-blot and PCR are discussed. The use of the IFA test as a diagnostic means for E. canis is presented along with its potential pitfalls. The review emphasizes that the disease process, cross-reactivites with other ehrlichial species, multiple tick-borne infections and persistent IFA antibody titers post-treatment, should all be considered when interpreting E. canis serological results. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Ehrlichia canis; Ehrlichial species; Serological testing * Corresponding author. Tel.: +972-8-9381461; fax: +972-8-9401240. E-mail address: wanertnt@shani.net (T. Waner). 0304-4017/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0304-4017(00)00407-6