A Field Recombinant Strain Derived from Two Type 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV-1) Modified Live Vaccines Shows Increased Viremia and Transmission in SPF Pigs

Abstract

In Europe, modified live vaccines (MLV) are commonly used to control porcine reproductive and respiratory syndrome virus (PRRSV) infection. However, they have been associated with safety issues such as reversion to virulence induced by mutation and/or recombination. On a French pig farm, we identified a field recombinant strain derived from two PRRSV-1 MLV (MLV1). As a result, we aimed to evaluate its clinical, virological, and transmission parameters in comparison with both parental strains. Three groups with six pigs in each were inoculated with either one of the two MLV1s or with the recombinant strain; six contact pigs were then added into each inoculated group. The animals were monitored daily for 35 days post-inoculation (dpi) for clinical symptoms; blood samples and nasal swabs were collected twice a week. PRRS viral load in inoculated pigs of recombinant group was higher in serum, nasal swabs, and tonsils in comparison with both vaccine groups. The first viremic contact pig was detected as soon as 2 dpi in the recombinant group compared to 10 and 17 dpi for vaccine groups. Estimation of transmission parameters revealed fastest transmission and longest duration of infectiousness for recombinant group. Our in vivo study showed that the field recombinant strain derived from two MLV1s demonstrated high viremia, shedding and transmission capacities.

A recombination between two Type 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV‐1) vaccine strains has caused severe outbreaks in Danish pigs

“…An experimental study from France revealed that the Porcilis/ Unistrain recombinant virus describe above (Renson et al, 2017) seems to be more virulent than the two parent PRRSV-1 vaccine viruses (Eclercy et al, 2019). However, this study did not assess if the increased virulence of the recombinant virus reflected that the recombinant virus was adapted to swine or if it was a result of the recombination per se.…”

Molecular and Cellular Mechanisms for PRRSV Pathogenesis and Host Response to Infection

“…RNA recombination has experimentally been proven by coinfections of cells or swine with two different strains of PRRSV (Liu et al, 2011;Yuan et al, 1999). During the recent epidemiological investigations, recombination has been detected between two wild-type PRRSV strains (Franzo et al, 2014;Kwon et al, 2019;Zhao et al, 2015), between wild-type PRRSV and MLV vaccine (Bian et al, 2017;Wang et al, 2019a;Zhou et al, 2018) or between MLV vaccine strains (Eclercy et al, 2019).…”

Bekämpfung des Porzinen Reproduktiven und Respiratorischen Syndroms in Sachsen und Thüringen

“…Aufgrund der in dieser Studie nicht erfolgten Unterscheidung zwischen Impf-und Feldviren ist auch denkbar, dass die erhöhten PCR-Nachweise in den Betriebsjahren mit Impfung von Impfviren stammten. Da bekannt ist, dass die PRRS-Viren eine hohe Mutationsrate besitzen und Virulenzgene zwischen Impfund Feldstämmen ausgetauscht werden können [32] [33], sollte eine hohe Viruszirkulation im Bestand stets vermieden werden. Nach erfolgreicher Stabilisierung sollte deshalb eine weitere Bestandsimpfung, insbesondere unter Einsatz von Lebendimpfstoff gegen PRRSV, einer kritischen Prüfung unterliegen und überlegt werden, ob andere Maßnahmen eventuell einen ähnlichen Erfolg haben können.…”