Microscopic Detection, Hematological Evaluation and Molecular Characterization of Piroplasms from Naturally Infected Dogs in Rio de Janeiro, Brazil.

Purpose: This study aimed to analyze the frequency of piroplasmids in the blood of dogs in Rio de Janeiro, compare the performance of microscopic techniques, assess the risk factors associated with infections and also molecularly and morphologically characterize the piroplasmids identified.

Methods: In all, 407 blood samples were collected from dogs between 2018 and 2019. These were subjected to microscopic parasitological techniques for thin and thick smears, stained with Giemsa and using a rapid staining kit. The slides were read under an optical microscope and the protozoa were characterized morphometrically. In addition, the blood samples were subjected to molecular characterization for diagnosing piroplasmid species using primers that amplified the gene 18S rRNA.

Results: Piroplasmids were detected in 38 (9.3%) samples. Of these, 33 samples presented nucleotide sequences compatible with Babesia vogeli. Most of the positive samples were young, male, defined breeds dogs that had been attended in clinics in São Gonçalo city. Thrombocytopenia and leukopenia were the hematological alterations more observed in positive samples, but positive samples without alterations were also detected. The sex was the only variable that showed statistical differences. Males dogs being more often infected than females (p < 0.05). The microscope slides mostly showed piriform and oval merozoites measuring greater than 2.5 µm in length, which were compatible with B. vogeli. However, smaller forms were also identified, thus demonstrating the polymorphic nature of this parasite.

Conclusion: Babesia vogeli was detected in blood samples from dogs in the metropolitan cities of Rio de Janeiro by molecular techniques in different parasite morphotypes.