Molecular epidemiology of canine parvovirus type 2 (CPV-2) in Italy

In this study, we performed phylodynamic analysis of 107 VP2 sequences of CPV strains detected in dogs showing clinical signs of gastroenteritis, collected during the period 1994–2013. The age of these animals ranged between two months and ten years, with or without vaccination history from different breeds and both genders. The majority of faecal samples were collected in the continental area of North and Central Italy and twenty-nine faecal samples came from Sicily. VP2 genes were sequenced and a variety of statistical analyses of nucleotide polymorphism and sequence variability were performed on the sequence data. Maximum likelihood phylogenetic trees were estimated using PAUP* version 4.0, with the best-fit model of nucleotide substitution determined using JModeltest 2. The HKY + I + Γ substitution model was optimal for all the sequence data (including reference strains), whereas the GTR + I + Γ substitution model was used for the sequences analysed in this study; the key parameter values (the HKY and GTR substitution matrix, the proportion of invariant sites I and the gamma distribution of rate variation with eight categories) were estimated from the data. To assess support for individual nodes, bootstrap resampling values were estimated with 1,000 neighbor-joining trees, again employing PAUP*. Molecular phylogenetic analysis of the amino acid sequences with a maximum likelihood method was carried out using the software PHYLIP version 3.695. The best substitution model for amino acid sequences was estimated using MEGA version 5.2.2. The JJT + Γ substitution model was optimal for the protein dataset and used to build phylogenetic trees. Typing of CPV strains detected fifty-six CPV-2a strains, twelve CPV-2 b strains, and thirty-nine strains characterized as CPV-2c. Sixty-one genetically distinct sequences or nucleotide sequence types (ntSTs) and nineteen amino acid sequence types (aaSTs) were identified among the 107 viruses sequenced. In the ten-year observation period, the frequency of the CPV variants showed rapid oscillations.