Abstract:

Genomic homology of ORF 5 gene sequence between modified live vaccine virus and porcine reproductive and respiratory syndrome virus challenge isolates is not predictive of vaccine efficacy

Tanja Opriessnig, DVM; Francisco J. Pallarés, DVM, PhD; Dachrit Nilubol, DVM, PhD; Amy L. Vincent, DVM, PhD; Eileen L. Thacker, DVM, PhD, Diplomate ACVM; Eric M. Vaughn, DVM, PhD; Michael Roof, DVM, PhD; Patrick G. Halbur, DVM, PhD

PDF version is available online.

Objective: To test the efficacy of Ingelvac PRRS ATP (Boehringer Ingelheim Vetmedica Inc, St Joseph, Missouri), a modified live virus (MLV) vaccine, to protect against respiratory disease and lesions induced by challenge of growing pigs with one of three porcine reproductive and respiratory syndrome virus (PRRSV) field isolates (SDSU73, VR2385, and Mn-01-A1). On the basis of genome sequencing of open reading frame (ORF) 5, these three isolates vary considerably from each other (72% to 86% homology) and from the Ingelvac PRRS ATP vaccine (76% to 89% homology).

Materials and methods: Seventy-three 2-week-old segregated early weaned pigs were randomly divided into seven groups of 10 pigs and one group of three pigs. Four groups were vaccinated intramuscularly with 2.0 mL of Ingelvac PRRS ATP MLV vaccine and four groups were not vaccinated. Three vaccinated groups were inoculated intranasally 38 days later, each with a different PRRSV isolate (5.0 mL of 10^5.8 median tissue culture infective doses). Three nonvaccinated groups were similarly challenged. One vaccinated and one nonvac-cinated group were sham-inoculated. Necropsy was performed on all pigs 14 days postinoculation.

Results: In vaccinated challenged pigs, compared to nonvaccinated challenged pigs, clinical disease was less severe (P < .05), average daily gain was greater (P < .001), and gross and microscopic lung lesions were less severe (P < .001).

Implication: Under the conditions of this study, the degree of ORF 5 homology between the MLV PRRSV vaccine and the infecting strain is not a good predictor of vaccine efficacy.

Keywords: porcine reproductive and respiratory syndrome virus, PRRSV, vaccine, heterologous challenge, efficacy

Cite as: Opriessnig T, Pallar?s FJ, Nilubol D, et al. Genomic homology of ORF 5 gene sequence between modified live vaccine virus and porcine reproductive and respiratory syndrome virus challenge isolates is not predictive of vaccine efficacy. J Swine Health Prod 2005;13(5):246-253.

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