Epidemiological and Molecular Investigation of Dirofilaria repens, Dirofilaria immitis, and Acanthocheilonema reconditum in Dogs in the Republic of Srpska (Bosnia and Herzegovina).

Canine filariosis is an emerging vector-borne parasitic disease of veterinary and public health importance, caused primarily by D. immitis and D. repens. The present study investigated the prevalence, risk factors, diagnostic performance of different methods, and molecular characteristics of filarial infections in dogs from the Republic of Srpska (Bosnia and Herzegovina). Blood samples from 418 dogs collected between 2020 and 2024 were examined using a modified Knott test, antigen enzyme-linked immunosorbent assay, and polymerase chain reaction-based methods. Overall, 21.3% of dogs were positive for at least one filarial species. D. repens was the most prevalent species (13.40%), followed by D. immitis (10.8%) and A. reconditum (1.4%). Coinfections with D. immitis and D. repens were detected in 3.35% of dogs, while triple infections occurred in 0.5%. Several individual and environmental factors were associated with an increased risk of infection, including poor body condition, mixed-breed status, inadequate parasite control, and specific movement histories. PCR showed the highest diagnostic performance for all detected species, outperforming both microscopy and antigen testing. Phylogenetic analysis revealed genetic diversity among the detected isolates and demonstrated their relationship to strains previously reported from other European countries. These findings confirm the endemic presence of canine filarial infections in the Republic of Srpska and emphasize the importance of molecular diagnostics, surveillance programs, and preventive measures for effective disease control.