Challenge of Naïve and Vaccinated Pigs with a Vaccine-Derived Recombinant Porcine Reproductive and Respiratory Syndrome Virus 1 Strain (Horsens Strain)

Abstract

In July 2019, a vaccine-derived recombinant Porcine reproductive and respiratory syndrome virus 1 strain (PRRSV-1) (Horsens strain) infected more than 40 Danish sow herds, resulting in severe losses. In the present study, the pathogenicity of the recombinant Horsens strain was assessed and compared to a reference PRRSV-1 strain using a well-characterized experimental model in young SPF pigs. Furthermore, the efficacies of three different PRRSV-1 MLV vaccines to protect pigs against challenge with the recombinant strain were assessed. Following challenge, the unvaccinated pigs challenged with the Horsens strain had significant increased viral load in serum compared to all other groups. No macroscopic changes were observed at necropsy, but tissue from the lungs and tonsils from almost all pigs were PRRSV-positive. The viral load in serum was lower in all vaccinated groups compared to the unvaccinated group challenged with the Horsens strain, and only small differences were seen among the vaccinated groups. The findings in the present study, combined with two other recent reports, indicate that this recombinant “Horsens” strain indeed is capable of inducing infection in growing pigs as well as in pregnant sows that is comparable to or even exceeding those induced by typical PRRSV-1, subtype 1 strains. However, absence of notable clinical signs and lack of significant macroscopic changes indicate that this strain is less virulent than previously characterized highly virulent PRRSV-1 strains.

Virological and Histopathological Findings in Boars Naturally Infected With Porcine Reproductive and Respiratory Syndrome Virus Type 1

“…This study is an extension of previous studies performed in relation to the PRRSV-1 infection at a boar stud in Denmark in 2019 described by Kristensen et al (2020) and Kvisgaard et al (2020 , 2021) . PRRSV-1 infection of the boars was confirmed by (i) detectable specific antibodies against PRRSV, (ii) detection of PRRSV-1 RNA in sample material, and (iii) discovery of PRRSV-1 positive cells by IHC.…”

“…In extractions, known PRRSV-positive and PRRSV-negative controls were included. The full procedure was performed as previously described ( Kvisgaard et al, 2021 ). All serum, semen, and tissue samples were analysed using RT-PCR as previously described ( Wernike et al, 2012 ).…”

Impacts of Quarterly Sow Mass Vaccination with a Porcine Reproductive and Respiratory Syndrome Virus Type 1 (PRRSV-1) Modified Live Vaccine in Two Herds

“…In extractions, known PRRSV-positive and negative controls were included. The full procedure was performed as previously described [22]. All serum and udder wipe samples were analysed by RT-qPCR [23] in pools of five, and OF in pools corresponding to each stable as previously described [23].…”

Heterologous vaccine immunogenicity, efficacy, and immune correlates of protection of a modified-live virus porcine reproductive and respiratory syndrome virus vaccine

“…The inability of a vaccine to clear from the blood can potentially lead to vaccine shedding: this shedding has become a significant concern of MLV vaccines (Huang and Meng, 2010;Rowland and Lunney, 2017). Furthermore, the prolonged prevalence of a PRRSV vaccine strain can lead to recombination and the emergence of new strains: in Denmark, an MLV vaccine and field strain recombined into a new virulent PRRSV-1-strain named Horsens (Kvisgaard et al, 2021). Therefore, along with offering broad protection, a safe vaccine should not only not (or minimally) be shed but it should also be cleared from the blood.…”

“…The respiratory diseases alone have caused an approximate 7.4% drop in annual production output, translating to over $664 million lost annually in the US (Valdes-Donoso et al, 2018). Along with its immunosuppressive capacities (Loving et al, 2015), PRRSV's high mutation rate allows it to evade the host's immunity provided either by infection or vaccination (Shi et al, 2010;Murtaugh and Genzow, 2011;Geldhof et al, 2012;Rowland and Lunney, 2017;Zhou et al, 2017;Kvisgaard et al, 2021). These mutations led to a plethora of strains: PRRSV can be divided into two species, type-1 or PRRSV-1, mainly found in Europe, and type-2 or PRRSV-2, prevalent in North America (Brinton et al, 2021).…”