Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 24, 1999
Publication Date: N/A
Interpretive Summary: Porcine reproductive and respiratory syndrome (PRRS) made its world debut in North Carolina in 1987. Since that time it has spread throughout North America and much of the rest of the world to become one of the most economically important diseases faced by swine industries worldwide. One of the most promising means for control of PRRS is through the use of vaccines. For these to be used safely and effectively we need to know the best time for their administration. This study addresses the issues of safety and efficacy of live-PRRS virus (PRRSV) vaccines being administered to pregnant gilts. Although we found no evidence that this practice was unsafe, it provided only partial protection against subsequent exposure of vaccinated gilts to a virulent (i.e. disease-producing) strain of PRRSV. As a result the veterinary practitioner will be alerted to the importance of administering PRRS vaccines well before gestation. The proper use of vaccines, including the most appropriate time for their administration, is an important aspect of the control of this costly disease.
Technical Abstract: Objective: To determine the safety and efficacy of vaccinating pregnant gilts near mid-gestation with an attenuated strain of porcine reproductive and respiratory syndrome virus (PRRSV). Animals: 16 pregnant gilts. Procedure: Groups of pregnant gilts (4 gilts/group) free of antibody for PRRSV were: 1) kept as untreated controls (group I); 2) vaccinated at or about 60 days of gestation (group II); 3) vaccinated at or about 60 days of gestation and exposed to virulent PRRSV at or about 90 days of gestation (group III); or 4) exposed to virulent PRRSV at or about 90 days of gestation (group IV). The safety and efficacy of vaccination was evaluated primarily by group comparisons of prenatal and postnatal survival of fetuses and pigs, respectively, and by the condition and rate of weight gain of liveborn pigs. Results: Collective (prenatal and postnatal) death losses up to postfarrowing day 15 (when the experiment was ended) were about the same for groups I (14.9%) and II (16.9%). They were greater for group III (36.7%), and were still greater for group IV (62.2%). Pig average body weights at day 15 were the greatest for group I (4.46 kgm), and progressively less for the other groups (3.87 kgm, 3.76 kgm, and 2.18 kgm for groups II, III, and IV, respectively). Conclusion: Under conditions of this study, vaccination near midgestation appeared to be safe. However, it provided only partial protection against subsequent exposure to virulent virus. Clinical Relevance: Attenuated-PRRSV vaccines may have to be administered to naive gilts more than 30 days before conception to provide maximum protection throughout gestation.