Spatial distribution and molecular epidemiology of Babesia vogeli in household dogs from municipalities with different altitude gradients in the state of Rio de Janeiro, Brazil.

We performed a cross-sectional epidemiological study with 456 household dogs from urban and rural areas in two different regions situated at different altitudes in the state of Rio de Janeiro. The PCR technique using 18S rRNA as target revealed prevalence of 7.9% of dogs positive for piroplasmids. These samples were sequenced, and all the sequences were 99.9% to 100% similar to Babesia vogeli sequences from other countries. The spatial distribution of positive cases was analysed using kernel interpolation in the QGIS software, and the spatial correlation indicators among positive dogs, altitude, and presence of ticks were obtained by calculating the local Moran index using the GeoDa software. The spatial correlation between positive cases and altitude was clear based on both visual and statistical observations. Logistic regression applying the Wald method with a cutoff point of 0.1 revealed that dogs from a region with altitude <600 m had a 2.29-fold chance of B. vogeli infection (OR = 2.29; p-value = 0.04; CI: 1.03-5.07), while the rainy season was 2.45 times more associated with B. vogeli infection (OR = 2.45; p-value = 0.01; CI: 1.20-5.01), and dogs infested with Rhipicephalus sanguineus sensu lato had a 2.47 times higher chance of being infected (OR = 2.47; p-value = 0.02; CI: 1.13-5.38). Entropy analysis of the alignment between B. vogeli 18S rRNA (> 1.600 bp) sequences revealed that the most variable region corresponds to the hypervariable V4 region. Genetic homogeneity was observed among the B. vogeli 18S rRNA sequences, with distance values ranging from 0 to 0.007 and a mean value of 0.001. The evolutionary distance (0.003) was greater between the sequences from the municipalities of Barra do Pirai (low altitude) and Teresopolis (high altitude). This study expands the molecular epidemiologic knowledge of B. vogeli and shows points of variability in the B. vogeli 18S rRNA. The results indicate the potential use of spatial analysis tools to improve screening for positive cases, enabling more in-depth studies to strengthen understanding of tick infection prevention in dogs.