Molecular Characterization and Genetic Diversity of Ehrlichia canis in Naturally Infected Dogs from the Unaí Microregion, Minas Gerais, Brazil.

Ehrlichia canis is an obligate intracellular bacterium responsible for canine monocytic ehrlichiosis and is widely distributed in tropical and subtropical regions. This study investigated the occurrence and genetic diversity of E. canis in naturally infected dogs from the Unaí microregion, Minas Gerais, Brazil, using the trp19, p28, and trp36 genes as molecular markers. A total of 386 whole blood samples were initially screened by conventional PCR targeting the Anaplasmataceae 16S rRNA gene, yielding 38 positive samples (9.8%). Subsequent PCR targeting the E. canis trp19 gene confirmed infection in 21 samples (5.4%). Among these, 12 samples were positive for the p28 gene and eight for the trp36 gene. Sequence analysis of p28 revealed high nucleotide identity (99.27-99.88%) with reference strains and amino acid substitutions. Haplotype network analysis identified nine p28 haplotypes, indicating substantial intraspecific genetic diversity. Analysis of the trp36 gene demonstrated the co-circulation of Brazilian and American genogroups, with variation in tandem repeat copy number. These findings reveal a genetically heterogeneous E. canis population in the Unaí microregion and provide evidence of the co-circulation of distinct lineages. The combined use of multiple molecular markers improved the characterization of the circulating strains and contributes to a better understanding of the molecular epidemiology and population diversity of E. canis in Brazil.