Molecular characterization of Ehrlichia canis trp36 sequences in dogs from northern Sardinia, Italy

Canine monocytic ehrlichiosis (CME), caused by Ehrlichia canis, is a major tick-borne disease of dogs in Mediterranean regions, although information on the genetic diversity of circulating genetic variants remains limited. This study investigated the molecular characteristics of E. canis in 75 dogs from Sardinia, Italy. All samples were confirmed positive by nested PCR targeting the 16S rRNA gene, while the polymorphic trp36 gene was successfully amplified in 32 samples and completely sequenced in 21 samples. The trp36 sequences showed high similarity with E. canis sequences previously reported from Taiwan, Iran, Turkey, Australia and China and contained the conserved TEDSVSAPA tandem repeat motif, with 6-15 repeat copies. Amino acid substitutions were identified in the N- and C-terminal regions, contributing to the observed genetic variability among the Sardinian sequences. Phylogenetic analysis assigned all Sardinian sequences to the Taiwan (TWN) genogroup, in which the international strains resolved into a separate, highly supported subclade. These findings provide the first molecular characterization of the E. canis trp36 gene in Sardinia, identifying closely related variants and expanding current knowledge of the genetic diversity of E. canis in this Mediterranean region.