Hemagglutinin Gene Diversity of Canine Distemper Virus from Clinical Samples in Brazil

Canine distemper virus (CDV) affecting both domestic dogs and wild animals, resulting in high rates of morbimortality. The viral genome encodes six different proteins where the Hemagglutinin is the most variable, being the basis for molecular phylogenetic analysis and may lead to antibody recognition mismatch and vaccine failure. The study aimed to analyze the H gene of the CDV in field samples from naturally infected dogs in Brazil. A total of 24 blood, urine and ocular discharge samples were collected from naturally infected dogs from endemic areas of Brazil. RNA from clinical samples of infected animals was extracted, PCR products of H gene amplification were aligned, the sequences of samples were submitted to a public database search and were aligned with the protein sequence of the Onderstepoort CDV vaccine strain to explore their similarity profiles. Sequencing of the fragments that represent the entire H gene sequence demonstrated five distinct isolates. The phylogenetic analysis of the isolates showed that they belong to the cluster Europe/South America-1, differing substantially from the vaccine strains used in the country. Generated amino acids analyzed, showed that the specific substitutions at the SLAM receptor site of the H gene, previously linked to the emergence of diseases in new hosts, were not detected in these sequences. However, the R580Q substitution detected in the isolated strain from Pernambuco is considered imminently deleterious to the efficiency of fusion and expression of the surface of the binding protein. These findings demonstrate that the genetic variability identified in field strains of the distemper virus in endemic areas in Brazil shows genetic alterations that may lead to antibody mismatch.