Comparative Efficacy Evaluation of Two Modified-Live PRRS Vaccines
G. Haiwick, A. Neubauer, J. Hermann, M. Roof, B. Fergen, R. PhilipsJune 7, 2017
The implementation of a systematic methodology for PRRS control that utilizes modified-live vaccine (MLV) for the control of wild typePRRSV infections can mitigate the consequences of infection on health and performance. It is necessary for MLV to be effective against heterologous challenge with current PRRSV field isolates. The objective of this study was to directly compare the efficacy of Ingelvac PRRS® MLV (Boehringer Ingelheim Vetmedica, Inc., St. Joseph, MO) and Prime PacTM PRRS+ (Merck Animal Health, Omaha, NE) against a heterologous PRRSV challenge.
MATERIALS AND METHODS
The study was performed in seventy, PRRS naïve three-week-old pigs. On Day 0, Group 1 (n=20) was vaccinated with Ingelvac PRRS® MLV (2ml IM per label). Group 2 (n=20) was vaccinated with Prime PacTM PRRS+ (1ml IM per label). Group 3 (n=20) was a non-vaccinated challenge control group (NVC). Group 4 (n=10) was an IngelvacPRRS® MLV vaccinated, non-challenged group. On Day 28, Groups 1, 2 and 3 were challenged intranasally with 2.0ml containing 4.1logTCID50/ml of virulent PRRSV SDSU-73. On Day 42, 10 pigs were selected from each of Groups 1–3, necropsied, and lung lesions scored. The study was terminated on Day 70 and the remaining pigs were necropsied and lung lesions scored. Blood was collected from all pigs to assess the serologic response and viremia (Quantitative PCR; BIVI HMC Ames, Iowa). Rectal temperatures and ADWG were also measured and evaluated.
Both vaccinated groups demonstrated a large reduction in PRRSV associated lung lesions (Group 1, 0.5%; Group 2, 1.3%) compared to NVC (28.6%–median lung lesion) at day 42. At day 70, lung lesions had essentially resolved in all treatment groups. From day 42 to 63, Group 1 demonstrated fewer percent PCR positive pigs than the Group 2 and NVC pigs. The reduction of viremia following challenge occurred earlier in the Group 1 compared to the Group 2, and the pattern of viremia reduction in Group 2 was similar to the NVC. Group 1 maintained lower average temperatures throughout the challenge phase (days 28–42) compared to Group 2 and challenge control group. Between days 28 and 70, Group 1 had a 17% higher ADWG when compared to both the Group 2 and the NVC. Group 4 (vaccinated, non-challenged) demonstrated the best ADWG across treatment groups.
DISCUSSION AND CONCLUSION
Virulent PRRSV challenge has a biologic impact as measured by increased temperature and viremia and their influence on ADWG. This study is another example demonstrating the ability of modifiedlive PRRS vaccines to protect against a relevant PRRSV challenge. Implementing vaccine in a systematic methodology for PRRS control can mitigate the consequences of infection and subsequently improve the health and performance of pigs.
Table 1: Study Design
Table 2: Day 42 lung lesions (median %) and ADWG in vaccinated and non-vaccinated pigs challenged with PRRSV SDSU-73
Figure 1: Percentage of viremic pigs per treatment group following PRRSV SDSU-73 challenge
Figure 2: Average daily temperature by treatment group