Different Shedding Patterns Measured by Virus Isolation and Real-Time PCR in Pigs Challenged with Aujeszky’s Disease Virus

Aujeszky’s Disease (AD) is a major pig disease that accounts for devastating economic losses to pig industry. AD is controlled by containment of infected herds, use of vaccines and removal of latently infected animals. In endemic areas, control programmes against AD rely on the use of vaccines that efficiently limit the replication of virulent virus in infected pigs. The presented study investigated the efficacy of a live vaccine, administered to the pigs by the intramuscular route in an oil/water emulsion adjuvant, to reduce the excretion of challenge virus by vaccinated pigs using virus isolation and real-time PCR (qPCR) to determine the amount of excreted virus. Both virus detecting assays showed that the vaccinated animals shed significantly lower amount of virus than the nonvaccinated controls, and the quantity of the shed viruses decreased over time. Interestingly, while in the non-vaccinated control animals the virus titres detected by virus isolation and qPCR were approximately the same, in the vaccinated ones the amount of viable virus measured by virus isolation was consistently less than those detected by qPCR. These findings indirectly demonstrate that vaccination with a live virus induces effective local immunity at the primary site of replication, which reduces shedding and transmission of challenge virus. The results also pointed out that qPCR detection of the viral nucleic acid is not equal with viable viruses, which should be considered when interpreting the outcome of virus detecting assays.