Abstract
Simple SummaryModified live virus (MLV) vaccines are considered as the key component to control the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). The majority of pig farms apply the ‘mass’ vaccination strategy in breeding female animals. However, this PRRS MLV vaccination protocol involves the risk of inoculation of sows in the last stage of gestation, resulting in possible infection of the fetus as the virus can efficiently cross the placenta during the last period of pregnancy. Thus, we evaluated the ability of the vaccine virus to act as a pathogenic strain, to be transmitted to fetuses and to affect the health status of neonatal piglets. The results indicated that the study gilts transmitted the vaccine virus to their offspring, as well as that the PRRSV-infected piglets showed a poor clinical performance. Consequently, the pig farms that apply PRRS MLV vaccination in a routine blanket vaccination strategy must avoid inoculating pregnant gilts the last week before their parturition.The objective of the present study was to evaluate the potential risks of the four commercial PRRS-1 MLV vaccines in pregnant vaccinated gilts at the last stage of gestation under field conditions. The study was conducted at four pig farms, including 25 gilts from each farm (25 × 4 = 100 gilts), which were equally allocated to five different study groups. A PRRS-1 MLV vaccination was applied on the 100th day of their pregnancy with the different commercial vaccines that are available in the Greek market. The results indicated virus congenital infection and viremia in piglets (20/200 = 10% PRRSV infected piglets), and detection of PRRSV-specific antibodies (181/200 = 90.5% piglets found with PRRSV antibodies). The subsequent phylogenetic analyses revealed high percentages of similarity between the PRRSV-1 strain detected in infected litters and the PRRSV-1 vaccine strain to which the study gilts had been previously exposed to. Health status analyses of trial piglets resulted in differences between litters from vaccinated sows and litters from non-vaccinated sows at 110th day of gestation as regards the number of weak-born piglets, mummies, and piglets with splay-leg and/or respiratory symptoms. The current study’s results indicate several potential dangers of the PRRS MLV vaccination in late gestation.
Highlights
The porcine reproductive and respiratory syndrome virus (PRRSV) is considered to be one of the most challenging pig diseases having a significant economic impact on the swine industry
modified live virus (MLV) vaccines are considered to be the dominant ones in the field, as they are more effecMLV vaccines are considered to be the dominant ones in the field, as they are more effective in reducing the duration of viremia, virus shedding, disease occurrence, and severity compared to the PRRS killed virus (KV) vaccines [14,15,17,19,20,21]
Our study demonstrates that PRRSV vaccine strains can act as an infectious strain when PRRS MLV vaccination is applied in late gestation, affecting the health and immune status of piglets
Summary
The porcine reproductive and respiratory syndrome virus (PRRSV) is considered to be one of the most challenging pig diseases having a significant economic impact on the swine industry. The virus is considered to be one of the most important pathogens causing the porcine respiratory disease complex (PRDC), which is associated with huge economic losses in the global pig industry [11]. Recent estimates from Europe and North America show that the reproductive performance of infected herds is decreased by approximately 1.4 weaner pigs/sow. To these figures the costs arising from the effects of an endemic infection on mortality and morbidity, daily weight gain, feed efficiency, and treatment costs should be added [12]
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