background: Canine distemper virus (CDV) causes a highly infectious multisystem disease known as canine distemper (CD), which influence diverse species within the order of Carnivora. The virus shows genetic diversity, particularly within the hemagglutinin (H) gene region. The H protein is an important target in molecular studies due to its high divergence. Since vaccination program is conducted in Iran, CD still remains as one of the major causes of death in dogs in this country.

Objective: To expand our understanding about the differences among commonly found strains and those ones included in vaccines to reconsider the current vaccination program and predict probable vaccination outcomes.

methods: Ocular and Nasal swabs were collected from 16 dogs suspected of CDV infection. PCR was conducted to confirm the detection and sequencing of samples and vaccines using forward and reverse primers. Nucleotide sequences were aligned using Bioedit and CLC Genomics Workbench. Phylogenetic analysis was carried out using MEGA 11 software programme

Results: Based on the phylogenetic analysis all the isolated strains were included in the Arctic lineages. Evaluation of the deduced amino acid sequences indicated substitutions in three amino acid residues compared to the Onderstepoort vaccine strain and Biocan one.

Alignment of these wild 16 H gene nucleotide sequences revealed identity level ranges from 99.8% to 99.9% compared to Onderstepoort vaccine strain (Table2). Similarity (99.84%-99.85%) was detected between Iranian H sequences and Biocan vaccine strain

Conclusion: The strains were isolated in the Arctic lineages. Due to the variation in the H gene sequences between the vaccine strains and the wild strains, the CDV lineages currently circulating in Iran differ from the identified lineages; America-1. We conducted this study to deepen our understanding in regard to differences among circulating and vaccine strains and predicting whether the reconsideration of vaccine program is warranted.