An attenuated live vaccine based on highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) protects piglets against HP-PRRS

Porcine infections with highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) cause significant morbidity and mortality and currently there are no effective vaccines for disease prevention. An attenuated strain, HuN4-F112, was obtained by passaging the HP-PRRSV HuN4 on Marc-145 cells (112th-passage). PRRSV-free pigs were inoculated intramuscularly with HuN4-F112 (102.0, 103.0, 104.0, 105.0 and 106.0 TCID50 for groups 1–5, respectively). The groups 3–5 could resist the lethal challenge and did not show any obvious changes in body temperature nor clinical signs throughout the experiment, the pathological lesions were milder and the gained weight at a greater rate (P < 0.05), compared to group 1 and control. Sequence analysis of the HuN4 passages showed a conserved epitope in GP5 protein was mutated (196QWGRL/P200 → 196RWGRL/P200), as a result the monoclonal antibody could not recognize the HuN4-F112 any more. These results suggested that the HuN4-F112 could protect piglets from lethal challenge and might be a candidate vaccine against the HP-PRRSV.