Abstract
Background:
Hepatozoon canis (H. canis) is an intracellular protozoan parasite transmitted by ingestion of infected ticks. It is responsible for canine hepatozoonosis, a disease that affects the health and well-being of dogs worldwide. The infection can range from subclinical to severe, depending on the host’s immune status and parasite burden. H. canis has been reported in multiple regions, but data on its prevalence and genetic characteristics in Vietnam, particularly in Can Tho City, remains limited.

Aim:
To determine the infection rate and genetic characteristics of H. canis in dogs in Can Tho City, Vietnam.

Methods:
A total of 359 suspected cases of H. canis presented to veterinary hospitals between January and November 2024 were investigated. Molecular diagnosis was performed using polymerase chain reaction (PCR), and positive samples were sequenced. The resulting sequences were compared with reference H. canis strains in GenBank to assess genetic similarity and variation.

Results:
The overall infection rate of H. canis was 0.75% and 9.47% among the surveyed dogs and suspected cases, respectively. Genetic analysis showed high similarity (98.88%–100%) between the three local and global reference strains. Four high-entropy loci were observed: 208 (G→A), 217 (T→C), 450 (C→T), and 474 (C→T), with the highest entropy at position 450 (0.682), suggesting regional genetic variation and potential selective pressure. Transition bias analysis revealed a strong preference for pyrimidine transitions (T↔C), indicating conservation in key regions.

Conclusion:
To the best of our knowledge, this is the first comprehensive genetic characterization of H. canis in dogs in Can Tho City. Despite a low prevalence of infection, genetic analysis revealed significant local variation. These findings enhance our understanding of the molecular epidemiology and evolution of H. canis and emphasize the need for further studies to elucidate the clinical implications of genetic polymorphisms.

Key words: Molecular epidemiology; Hepatozoon canis; Tick-borne pathogen; 18S rRNA gene; Vietnam.