Phenotypic characterization of a highly pathogenic Italian porcine reproductive and respiratory syndrome virus (PRRSV) type 1 subtype 1 isolate in experimentally infected pigs

Highly pathogenic (HP) isolates of the PRRS virus started emerging in North America and Asia in the late 1990s. More recently, they have emerged in Europe. These isolates are characterized by high viral loads, severe general clinical signs and high mortality, in sows, weaners and growers. Their genome shows a discontinuous aminoacids deletion in the non-structural protein 2 (NSP2). The present study was aimed at characterizing the clinical, pathological and immunological features of a highly pathogenetic, Italian PRRSV-1 subtype 1 isolate (PRRSV1_PR40/2014), following experimental infection in conventional 4-weeks-old pigs. The PRRSV1_PR40/2014 infected group showed severe clinical signs (high fever and dispnoea). Pathological lesions, including severe lymphocytopenia in bronchial lymph-nodes and thymus were also recorded. Higher serum PRRSV genome copies and lower virus neutralizing antibody titer were observed in the PR40 group, when compared to the group infected with a conventional PRRSV strain. The genetic analysis of the strain, and the phenotypic features observed in the field and reproduced in the experimental study, confirmed the high pathogenicity of the Italian PRRSV-1 subtype 1 PR40 isolate.