Evaluation of the diagnosis of Ehrlichia canis in dogs from Costa Rica, using blood smears and molecular technique

The objective of this study was to compare the results of the diagnosis of Ehrlichia canis in blood of dogs from the Central Valley of Costa Rica, using blood smears and the polymerase chain reaction (PCR). For this purpose, 300 blood samples of dogs suspected of suffering ehrlichiosis were used. Samples were obtained from different veterinary clinics and had been previously analyzed using blood smears, nested PCR, and, in some cases, the serological technique. In addition, the following information was obtained from each blood sample: geographical location of the veterinary clinic and data from the dog such as race, age, sex, and clinical signs.Of the total 300 samples analyzed, 147 (49.0%) were positive for E. canis, using a nested PCR, while 178 (59.3%) were reported with inclusions using blood smears. However, only 103 (57.9%) of the positive cases using blood smear resulted in the molecular diagnosis of E. canis; while of the 122 negative samples (no inclusions) 44 (36.0%) were positive using the PCR technique. Blood smear testing showed a sensitivity of 70.1% and a specificity of 51.0%; positive and negative predictive values were 57.9% of 63.9%, respectively, compared with the PCR technique. The logistic regression analysis showed a positive association (p<0.05) with the presence of inclusions, but not for age or sex, while highly significant differences were detected using the Student’s T-Test in the average hematocrit and hemoglobin variables between PCR positive and PCR negative dogs. Of the 30 samples previously evaluated by serological tests, 25.0% of seropositive cases and 36.4% of seronegative cases were positive in the molecular diagnosis of E. canis. Low levels of hematocrit and hemoglobin, together with clinical signs and inclusions detected in blood samples, represent a strong indication of ehrlichiosis infection.However, a molecular technique is required to confirm the diagnosis.