Submitted to: Pig Veterinary Society International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/1/1998
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Attenuated-virus vaccines are often used in herds clinically affected with a virulent strain of porcine reproductive and respiratory syndrome virus (PRRSV). Dual infections that are likely to result from this practice present a potential diagnostic complication in that vaccine virus may obscure the presence of virulent virus when samples are subsequently submitted for virus isolation. To determine the practical importance of this issue we tested the relative ability of attenuated (cell-culture-adapted) and virulent strains of PRRSV to replicate competitively in pigs exposed to mixtures of the two strains of at various relative concentrations. We found that even when pigs were exposed to a mixture of vaccine and virulent virus that contained a marked (10-million-fold) excess of the former, virulent virus quickly predominated and was the only strain identified in serum samples collected on postexposure days 7 and 14. On the basis of this evidence we concluded that vaccine virus is unlikely to obscure the presence of virulent virus if samples are collected during a period of acute infection.