Molecular epidemiology and emerging genotypes of canine distemper virus in Istanbul, Türkiye

Canine distemper virus (CDV) is a highly contagious, globally distributed pathogen that remains a serious concern even with available vaccines. In Türkiye, reports of CDV outbreaks among vaccinated dogs suggest the emergence of genetically divergent strains. This study investigated CDV prevalence, clinical correlations, molecular characteristics, and phylogenetic relationships in Istanbul, Türkiye, using rectal swabs from 202 clinically ill dogs (2018–2023). Results revealed a 27.2% infection rate (55/202), with significantly higher prevalence in puppies (< 6 months; p < 0.05). Clinical signs (fever, seizures, gastrointestinal distress) and hematological alterations (elevated neutrophils, reduced RBC counts) were strongly associated with infection (p < 0.05). Phylogenetic analysis of the hemagglutinin (H) gene revealed three circulating genotypes: Arctic-like (72%), Asia 1 (24%), and Europe (4%). Arctic-like strains clustered with Turkish and European variants, while Asia 1 strains closely matched Chinese lineages suggesting multiple introduction routes. Notably, amino acid substitutions in antigenic regions and glycosylation sites were identified, that may facilitate immune evasion, particularly concerning given Türkiye’s complex dog population dynamics. Our findings indicate the Arctic-like CDV lineage now dominates in Istanbul’s canine population. This study provides valuable insights into the epidemiology and genetic diversity of circulating CDV genotypes in Türkiye and its implications for vaccine efficacy. Continuous surveillance is critical to monitor emerging strains and optimize control strategies.