Prevalence of Ehrlichia canisinfection in thrombocytopenic dogs from Rio de Janeiro, Brazil

Background: Infection with Ehrlichia caniscauses a highly variable, multisystemic disease in dogs. Nevertheless, many clinicians in Rio de Janeiro, Brazil, use the presence of only thrombocytopenia to make a presumptive diagnosis of E canisinfection. Objective: The objective of this study was to determine the prevalence of E canisin thrombocytopenic dogs from Rio de Janeiro, Brazil, using polymerase chain reaction (PCR). Methods: Following DNA extraction of whole blood samples from 226 dogs, PCR assays were done using primers for rickettsial DNA (including Ehrlichiaspp, Anaplasma platysand A phagocytophilum) and using E canis-specific primers (16S rRNA gene). Dogs were grouped as thrombocytopenic and nonthrombocytopenic based on platelet counts. The null hypothesis that there was no difference in the prevalence of E canisin these groups was rejected at P< .05. Results: Thirty-six (32.1) of the thrombocytopenic dogs and 4 (3.5) of the nonthrombocytopenic dogs were positive for rickettsial gene sequences (P< .0001). Further, 30 (26.8) of thrombocytopenic dogs and 4 (3.5) nonthrombocytopenic dogs were positive for E canis-specific gene sequences (P< .0001). Conclusions: Although the prevalence of E canisinfection was higher in thrombocytopenic dogs, less than one third of these dogs had demonstrable E canisinfection. Thus, thrombocytopenia is not specific for the detection of E canisinfection and should not be used solely to establish a diagnosis of canine ehrlichiosis, even in a geographic area with relatively high disease prevalence.