Effect of the Modified Live Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Vaccine on European and North American PRRSV Shedding in Semen from Infected Boars

Abstract

The objective of the present study was to compare the effects of the modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine (Ingelvac PRRS MLV; Boehringer Ingelheim Animal Health, St. Joseph, MO) on European and North American PRRSV shedding in the semen of experimentally infected boars. The boars were randomly divided into six groups. Vaccinated boars shed the North American PRRSV at the rate of 10 0.1 to 10 1.0 viral genome copies per ml and 3.63 to 10 1.1 50% tissue culture infective doses (TCID 50 )/ml, respectively, in semen, whereas nonvaccinated boars shed the North American PRRSV at the rate of 10 0.2 to 10 4.7 viral genome copies per ml and 1.14 to 10 3.07 TCID 50 /ml, respectively, in semen. Vaccinated boars shed the European PRRSV at the rate of 10 0.1 to 10 4.57 viral genome copies per ml and 1.66 to 10 3.10 TCID 50 /ml, respectively, in semen, whereas nonvaccinated boars shed the European PRRSV at the rate of 10 0.3 to 10 5.14 viral genome copies per ml and 1.69 to 10 3.17 TCID 50 /ml, respectively, in semen. The number of genomic copies of the European PRRSV in semen samples was not significantly different between vaccinated and nonvaccinated challenged European PRRSV boars. The present study demonstrated that boar vaccination using commercial modified live PRRSV vaccine was able to decrease subsequent shedding of North American PRRSV in semen after challenge but was unable to decrease shedding of European PRRSV in semen after challenge.

Effects of North American Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)-Based Modified Live Vaccines on Preimmunized Sows Artificially Inseminated with European PRRSV-Spiked Semen

“…However, the vaccine was unable to decrease shedding of the European PRRSV in semen after a challenge (8). These results are clinically meaningful because the North American PRRSV-based vaccine could not protect swine from the European PRRSV.…”

“…Insemination doses were stored at 17°C and used immediately after extension. The raw semen samples tested negative for the presence of North American and European PRRSV RNA using real-time PCR (8,26).…”

“…RNA extractions from the serum samples from all sows used in this study were collected at Ϫ28, Ϫ25, Ϫ23, Ϫ21, Ϫ7, 0, 7, 14, 21, 35, 49, 56, 70, 85, 99, 105, and 115 dpi and performed as previously described (8,23). Real-time PCR for the European PRRSV and vaccine strains was used to quantify PRRSV genomic cDNA copy numbers using RNA extraction from serum samples, which was performed as previously described (8,23). A commercially available realtime, single-tube RT-PCR assay (Tetracore Inc., Gaithersburg, MD) for the detection of North American and European PRRSV was used to detect PRRSV RNA.…”

“…In addition, the PRRSV was diluted with Dulbecco's modified Eagle medium (DMEM) in a 1:1 dilution, which also served as a control. The PRRSV titer was estimated at 0, 8,24,48,72, and 96 h postdilution by immunofluorescence assays (IFAs) using a PRRSVspecific antibody (SR30) as described previously (17).…”

“…Recently, immunizing boars with the North American PRRSVbased modified live vaccine (Ingelvac PRRS MLV; Boehringer Ingelheim Animal Health, St. Joseph, MO) has been shown to decrease subsequent shedding of the North American PRRSV after a challenge (8). However, the vaccine was unable to decrease shedding of the European PRRSV in semen after a challenge (8).…”