Comparative analysis of immune responses following experimental infection of pigs with European porcine reproductive and respiratory syndrome virus strains of differing virulence

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is difficult to control due to a high mutation rate and the emergence of virulent strains. The objective of this study was to analyze the immunological and pathological responses after infection with the European subtype 3 strain Lena in comparison to subtype 1 strains Belgium A and Lelystad-Ter Huurne (LV). Sixteen pigs were inoculated per strain, and sixteen pigs with PBS. At days 7 and 21 post-inoculation (p.i.), four pigs per group were immunized with an Aujeszky disease vaccine (ADV) to study the immune competence after PRRSV infection. Infection with the Lena strain resulted in fever and clinical signs. This was not observed in the Belgium A or LV-infected pigs. Infection with the Lena strain resulted in high virus titers in serum, low numbers of IFN-γ secreting cells, a change in leukocyte populations and a delayed antibody response to immunization with ADV. Levels of IL-1β, IFN-α, IL-10, IL-12, TNF-α and IFN-γ mRNA of the Lena-infected pigs were increased during the first week of infection. For pigs infected with the Belgium A or LV strain, the effects of infection on these parameters were less pronounced, although for the Belgium A-infected pigs, the level of the analyzed cytokines, except for TNF-α, and leukocyte populations were comparable to the Lena-infected pigs. These results suggest that while the outcome of infection for the three strains was comparable, with mostly clearance of viremia at day 33 p.i, differences in immune responses were observed, perhaps contributing to their virulence.

Efficacy and safety of simultaneous vaccination with two modified live virus vaccines against porcine reproductive and respiratory syndrome virus types 1 and 2 in pigs

“…PRRSV-1, subtype 2 and subtype 3 viruses have only been detected east of Poland and are more than 20% different from the PRRSV-1 subtype 1 strains circulating elsewhere [23]. Only few studies have been performed with these diverse East-European strains, but a series of studies have revealed that at least some subtype 3 strains are more virulent than typical subtype 1 strains [35][36][37][38]. Recently, we have shown that some subtype 2 strains seem to be more virulent than subtype 1 strains [10] and in both the previous and the present study ILI6 induced more severe clinical signs and more pronounced viremia than the PRRSV-1, subtype 1 strains.…”

Comparison of Host Immune Responses to Homologous and Heterologous Type II Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Challenge in Vaccinated and Unvaccinated Pigs

“…However, the high incidence of genetic mutation during PRRSV transmission often results in vaccines based on strains of PPRSV isolated twenty years ago, such as MLV, having limited protection from new emerging viral strains. Disparity of immune responses elicited by different PRRSV strains was reported previously [10]. However, the role of humoral and cellular immune responses was not clearly elucidated in these reports with regard to the protection from virus challenge with different PRRSV strains.…”

Lung pathogenicity of European genotype 3 strain porcine reproductive and respiratory syndrome virus (PRRSV) differs from that of subtype 1 strains

“…The experimental protocol was described in detail by Weesendorp et al (2013a). In short, sixty-four five-weekold male pigs were obtained from a SPF herd, free of PRRSV, Mycoplasma hyopneumonia and Actinobacillus pleuropneumonia.…”

“…Viraemia was analysed in serum at days 0, 3, 5, 7, 10, 14, 21, 26 and 33 p.i. Results of viraemia were presented in detail by Weesendorp et al (2013a). Gross pathology examination of the lungs was performed by one examiner, who was blinded in regard to treatment.…”