Molecular Epidemiology of Babesia vogeli and Hepatozoon canis in Dogs from Urban and Peri-Urban Areas of Rio de Janeiro, Brazil.

Babesia vogeli is considered endemic in urban settings of Brazil, whereas Hepatozoon canis remains insufficiently documented in several regions, including the metropolitan area of Rio de Janeiro. This study investigated the frequency, spatial distribution, and determinants of infection by piroplasmids and Hepatozoon spp. in dogs from distinct environments. A total of 372 blood samples from pet dogs were collected between June and October 2023 in Maricá (Area 1; n = 105) and in the Administrative Regions of Barra da Tijuca, Guaratiba, and Jacarepaguá (Area 2; n = 267). Molecular screening was performed using 18S rRNA gene-based PCR assays, followed by sequencing and phylogenetic inference. Conventional PCR was used for piroplasmids, while both conventional and nested PCR were applied for Hepatozoon detection. Overall, 30 dog samples (8.1%) tested positive. Piroplasmids were detected in 3.5% of dogs, with a higher occurrence in Area 1, whereas Hepatozoon spp. infection was identified in 5.4% of samples, with co-positivity with piroplasmids being rare. All piroplasmid sequences corresponded to B. vogeli, while H. canis was confirmed in thirteen dogs. The absence of owner-reported tick-borne disease history was the main factor associated with hemoparasite positivity. These findings provide the first molecular epidemiological evidence of H. canis circulation in different areas of Rio de Janeiro and highlight the need for integrated diagnostics, surveillance, and targeted actions to improve control.