Start Date: Oct 17, 2013
End Date: Oct 01, 2014
Augmented DIVA-MLV (differentiating infected from vaccinated animals-modified live virus) preparations will be generated by co-transfection into MARC 145 cells of in vitro transcribed RNAs of a DIVA MLV infectious clone. Supernatants from these transfections will be passaged on MARC 145 cells to amplify the augmented vaccine virus. Expression and presence of the DIVA tag will be verified by ELISA and RT PCR, respectively. Groups of 4 week old swine will be vaccinated (day 0) with ~10**5-10**6 TCID50 intramuscularly and allowed to seroconvert for 28 days. There will also be a group which does not receive vaccination to serve as a control. Serum samples will be obtained weekly to monitor porcine reproductive and respiratory syndrome virus (PRRSV) seroconversion using a commercially available PRRSV ELISA kit. On day 28, all swine will be challenged with either a homologous strain (VR2332) or heterologous strain (SDSU73). Again, there will also be control groups which are vaccinated but not challenged with either PRRSV strain. Following challenge, animals will be monitored daily for clinical signs (lethargy, weight, temperature) and blood will be obtained on days 32, 35, 38 and 42 to monitor viral load and serum cytokine levels. On day 42, necropsies will be performed on all animals and tissue samples (lung, lymph node, thymus) as well as lung lavage fluid will be obtained. All tissue and fluid samples will be evaluated for viral load by RT qPCR. Data from non-vaccinated or MLV vaccinated control animals will be compared to animals who received augmented DIVA MLV vaccines to ascertain whether the augmented vaccines were able to provide better protection from PRRSV challenge.