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Bulletin No. 21 - Spring 2005
VirologyPorcine Reproductive and Respiratory Syndrome (PRRS)
JOHNSON W, ROOF M, VAUGHN E, CHRISTOPHER-HENNINGS J, JOHNSON CR, MURTAUGH MP
Pathogenic and humoral immune responses to porcine reproductive and respiratory syndrome virus (PRRSV) are related to viral load in acute infection.
Veterinary Immunology and Immunopathology, 2004, Volume 102, Nº3, 233-247
The virulence of 8 virulent and attenuated (cell-culture adapted) PRRSV isolates were investigated and compared. Each of the isolates was inoculated to a group of 10 pigs. Another group received a pool of all isolates and one group was kept as control. Blood samples were collected and examined at close intervals. Virus isolation was carried out and viremia was evaluated by real time quantitative RT-PCR. The humoral immune response to PRRSV was assessed by Herdcheck® PRRS ELISA 2XR and a PRRSV protein-specific ELISA was performed to determine the antibody titers against N, a structural protein, and nsp 4, a non structural protease. Body weight and clinical signs were also monitored. A high variability of levels of viremia following PRRSV exposure was observed. Virulent strains were found to replicate much better than attenuated strains. Moreover, virulent strains were shown to induce a faster and more intense humoral response than attenuated strains do. The nsp4 protease antibody response was low in all animals independently of the type of strain. By contrast, high levels of antibodies to the N protein were associated to the most virulent strains. Pigs inoculated with virulent strains had lower weight gains and higher death rates. Therefore, a clear relationship was established between viral load in acute infection and clinical expression/immune response of pigs to PRRSV.
