Studies on genetic properties of porcine parvoviruses

In the last years, it has been shown that some parvoviruses exhibit high substitution rates, close to those of RNA viruses. In order to monitor and determine new mutations of the porcine parvovirus (PPV), recent PPV field isolates from Austria, Brazil, Germany and Switzerland were sequenced and analyzed. These samples, together with sequences retrieved from GenBank, were included in three datasets (consisting of a VP1 complete gene, VP1 partial gene and NS1 complete gene). For each dataset, the nucleotide substitution rate and the molecular clock were determined. The analysis of the PPV field isolates revealed that a recently described amino acid substitution, S436-T, appears to be common in the VP2 protein in the Austrian, Brazilian and German virus population. Furthermore, new amino acid substitutions were identified, being mainly located in the viral capsid loops. By inferring the evolutionary dynamics of the PPV sequences, nucleotide substitution rates of approximately 10 nucleotide substitutions per site per year for the non-structural protein gene and 10 for the capsid protein gene (for both viral protein datasets) were found. The latter rate is similar to that commonly found in RNA viruses. An association of the phylogenetic tree with the molecular clock analysis revealed, that the mutations, on which the divergence for both capsid proteins is based, occurred in the last 30 years. Based upon these findings, one CHAPTER 3 HIGH EVOLUTION RATE IN THE PPV CAPSID PROTEIN 16 can conclude that PPV variants are continuously evolving and that vaccines, which are mainly based on strains isolated about thirty years ago, should possibly be updated.