Molecular Characterization of Canine Distemper Virus in Istanbul, Turkey

Abstract

Background: Canine distemper is a highly contagious, multisystem disease with global prevalence. It is caused by the Canine Distemper Virus (CDV), an enveloped, single-stranded RNA virus. Despite widespread vaccination, CDV outbreaks in fully vaccinated dogs in Turkey suggest the emergence of genetically distinct strains. The genetic variability and antigenic diversity of CDV pose challenges for effective vaccination and disease control. Continued surveillance in Turkey is essential to guide vaccine updates and enhance preventive measures. This study investigates the prevalence of CDV in suspected dogs, as well as its molecular characteristics and phylogenetic relationships in Istanbul, Turkey.Methods: During the canine disease surveillance program, 202 rectal swabs were collected from clinically ill dogs at the animal clinic of Istanbul University-Cerrahpaşa between 2018 and 2023. CDV was detected using real-time quantitative PCR (RT-qPCR) with previously described primers and protocols. The hemagglutinin (H) gene was partially sequenced to assess genetic diversity and evolutionary characteristics. Results: CDV was detected in 27.2% (55/202) of samples. Dogs under six months of age had a significantly higher infection rate (p<0.05), while gender, breed, and vaccination status showed no significant correlation with CDV prevalence (p>0.05). Clinical signs, including pyrexia, diarrhea, vomiting, and epileptic seizures, were significantly associated with CDV infection (p<0.05). Infected dogs exhibited higher pulse rates and elevated white blood cell (WBC) and neutrophil counts, while hemoglobin, hematocrit, and red blood cell (RBC) counts were significantly lower (p<0.05). Five samples did not produce high-quality sequences and were excluded from the nucleotide analysis. The nucleotide identity for H gene sequences was 83.6~100%, while amino acid identity was 75.46~100% among CDV strains. Phylogenetic analysis identified three CDV genotypes: Asia 1, Europe, and Arctic-like. Among the 50 CDV strains, 36 clustered with the Arctic genotype, 12 with Asia 1, and only two with Europe. Asia 1 strains closely resembled Chinese CDV strains, while Arctic-like strains were more similar to Turkish, Italian, Swiss, and Australian CDV strains. Amino acid analysis of the H protein revealed substitutions in antigenic regions and three potential asparagine glycosylation sites, suggesting selection pressure that may contribute to immune evasion and vaccine failure. Conclusion: This study provides valuable insights into the epidemiology of circulating CDV genotypes in Istanbul, Turkey. The findings underscore the high prevalence of breakthrough infections and the genetic diversity of CDV. The presence of mutations in antigenic regions suggests that emerging CDV genotypes may undermine the protective efficacy of existing vaccines. These findings highlight the need for continuous laboratory-based surveillance in both domestic and wild canines across Turkey to monitor distribution patterns, genotype emergence, and disease severity.