#02-033

Complete

Date Full Report Received

10/07/2004

Date Abstract Report Received

07/26/2006

Investigation

Institution:
Primary Investigator:

Neutralizing antibodies are those antibodies produced by a pig infected with PRRSV which, when mixed with PRRSV in a test tube, render it uninfectious by inactivation. Based on the results of previous experiments involving pregnant sows, we know that PRRSV neutralizing–antibodies may completely protect a sow against the infection with this virus. However, the results from this NPB project indicate that mechanisms of protective immunity mediated by these antibodies against PRRSV are different when comparing adult animals (pregnant sows) and young pigs. While a relatively low level of neutralizing antibodies in blood may fully protect sows against PRRSV-induced abortion, the amount of neutralizing antibodies necessary to obtain full protection of a young weaned pig against PRRSV generalized infection would be significantly higher. This inability of neutralizing antibodies to fully protect young pigs probably reflects differences in the level of multiplication of PRRSV in the body of young pigs and in adult animals. A young pig is known to contain cells that are significantly more sensitive to PRRSV than those of an adult animal such as a pregnant sow.This research indicates that protection by vaccines may be simpler to obtain in sows than in young pigs. While vaccination with a commercial vaccine may be effective against abortions, immunizing young, weaned pigs with the same vaccine would still remain more challenging. Important additional information obtained in this NPB project is that the measurement of viremia (PRRSV in blood) is not a trustable indicator of the infection status of the animal. We observed that an animal may be non-viremic but still replicate the virus abundantly in their tissues, efficiently transmitting the PRRSV infection to contact animals.