Genetic and pathogenic characterization of a Russian subtype 2 PRRSV-1 isolate

Porcine reproductive and respiratory syndrome virus (PRRSV) causes reproductive failure and respiratory problems. Data about the virulence and pathogenicity of subtype 2 PRRSV-1 strains are limited. The main purposes of this investigation were to characterize the full genome sequence of the subtype 2 PRRSV-1 WestSib13 strain and to compare the pathogenicity with that of the subtype 1 PRRSV-1 Lelystad strain. Comparison of the whole genome sequence of the WestSib13 strain with that of PRRSV-1 prototype strains revealed a 76.2% (subtype 1 Lelystad virus) and 79.0% (subtype 3 Lena virus) identity, respectively The virulence and pathogenicity of the European subtype 2 PRRSV strain WestSib13 and the European subtype 1 PRRSV strain Lelystad were compared in 3-week-old piglets upon inoculation of 10^5.4 TCID₅₀ of virus. Non-infected animals (control group) as well as animals infected with the Lelystad strain were clinically healthy until 14days post challenge. In contrast, animals infected with the WestSib13 strain demonstrated dyspnea starting at 3days post-inoculation (dpi). All piglets in this group died between 5 and 8 dpi. During that period, fever was not observed in WestSib13-infected animals. Viremia was detected in animals from both infected groups starting from 2 dpi. Viral loads in serum and lungs upon euthanasia were significantly higher (3 log₁₀) in the WestSib13-infected than in the LV-infected animals. Taken together, this study provides the full genome sequence and the unusual virological and clinical outcome (high level viremia without fever) of the novel WestSib13 strain.