This was an observational study that prospectively followed 29 breeding herds for 65 weeks in the U.S.A. that became infected with porcine reproductive and respiratory syndrome virus (PRRSv). The herds operated in a four-week batch farrowing system and adopted a load-close-expose strategy using a modified-live virus vaccine to achieve PRRSv stability. The purpose of this study was to describe time to stability (TTS) based on RT-qPCR testing for PRRSv RNA on processing fluid samples in herds undergoing PRRSv elimination, after implementing herd closure and mass exposure to a PRRS modified-live virus (MLV) vaccine. For the purpose of this study, stability was defined as consistently producing PRRSv-negative pigs. Study herds were monitored until two consecutive piglet batches tested PRRSv RT-qPCR negative, then 30 due-to-wean piglet sera from the second batch were tested for PRRSv RNA by RT-qPCR. Once the farm re-opened, sera from incoming naïve gilts were tested for anti-PRRSv antibodies by ELISA at 30- and 60-days post-entry to confirm negative status to PRRSv. Day zero was the day of whole-herd exposure to a commercial PRRS vaccine virus. Twenty-eight of 29 herds (96.55%) achieved TTS within the study period. TTS ranged from 18 to 55 weeks with a median of 27 weeks. Serum from due-to-wean piglets was collected on 28 farms, of which 26 (92.85%) obtained PRRSv RT-qPCR-negative results on the first collection. At the end of the observational period, 16 sow farms successfully re-introduced PRRSv-naïve gilts with no detected serologic response. In conclusion, the median time to achieve TTS in breeding herds being operated in a four-week batch farrowing system undergoing PRRSv elimination using load-close-expose with attenuated virus vaccine was 27 weeks. Also, processing fluid-based monitoring of breeding herds under PRRS elimination was practical and reliable to assess PRRSv stability.
Vaccination against porcine circovirus type 2 (PCV2) is commonly performed in piglets worldwide, and increasingly also in sows. We conducted a literature search and review to assess the potential interference of maternally derived antibodies (MDA) in piglets with vaccination against PCV2. The effectiveness of vaccination was compared to no vaccination in the presence of high levels of MDA (≥8 log2 IPMA titer), as reported in field studies. In total, 13 papers fulfilled the predefined inclusion criteria, allowing up to 24 comparisons per parameter. In the presence of high levels of MDA, vaccinated pigs had, on average, a 20 g/d higher mean daily weight gain and a 34% lower mortality compared to non-vaccinates. The maximum percentage of viremic pigs was reduced by 63% and the maximum viral load in serum was 0.72 log10 PCV2 DNA copies lower. Vaccination at 3 weeks of age was associated with the highest improvements in production parameters and reductions in viremia. Our findings suggest that the vaccination of piglets is effective with respect to production parameters and viremia even in the presence of high MDA, with an age of 3 weeks at vaccination being most beneficial.
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