Significance of serological testing for ehrlichial diseases in dogs with special emphasis on the diagnosis of canine monocytic ehrlichiosis caused by Ehrlichia canis

Dogs are susceptible to a number of ehrlichial diseases. Among them, canine monocytic ehrlichiosis 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.