Successive Inoculations of Pigs with Porcine Reproductive and Respiratory Syndrome Virus 1 (PRRSV-1) and Swine H1N2 Influenza Virus Suggest a Mutual Interference between the Two Viral Infections.

Juliette Bougon,Sophie Mahé,Mireille Le Dimna,Nicolas Barbier,Stéphane Gorin,Stéphane Quéguiner,Frédéric Paboeuf,Céline Deblanc,Patricia Renson,Olivier Bourry,Gaëlle Simon

doi:10.3390/v13112169

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza A virus (swIAV) are major pathogens of the porcine respiratory disease complex, but little is known on their interaction in super-infected pigs. In this study, we investigated clinical, virological and immunological outcomes of successive infections with PRRSV-1 and H1N2 swIAV. Twenty-four specific pathogen-free piglets were distributed into four groups and inoculated either with PRRSV at study day (SD) 0, or with swIAV at SD8, or with PRRSV and swIAV one week apart at SD0 and SD8, respectively, or mock-inoculated. In PRRSV/swIAV group, the clinical signs usually observed after swIAV infection were attenuated while higher levels of anti-swIAV antibodies were measured in lungs. Concurrently, PRRSV multiplication in lungs was significantly affected by swIAV infection, whereas the cell-mediated immune response specific to PRRSV was detected earlier in blood, as compared to PRRSV group. Moreover, levels of interferon (IFN)-α measured from SD9 in the blood of super-infected pigs were lower than those measured in the swIAV group, but higher than in the PRRSV group at the same time. Correlation analyses suggested an important role of IFN-α in the two-way interference highlighted between both viral infections.

Highlights

IL-6 and IL-10 concentrations were low and close to the quantification threshold of the enzyme-linked immunosorbent assay (ELISA) kits; we considered these cytokines to be induced when the optical density (OD) of the sample was higher than the basal level observed in uninfected pigs, i.e., the mean OD + 2 standard deviations calculated for the Control group
We investigated the possible interference between porcine reproductive and respiratory syndrome virus (PRRSV)-1 and swine influenza A virus (swIAV)
This model mimics as best as possible a situation most likely to be encountered in farms, taking into account the long-lasting and acute profiles of PRRSV and swIAV

Summary

Introduction

Among the viruses involved in PRDC, porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza A virus (swIAV) are among the most important primary agents [1] These viruses are both highly prevalent and enzootic in pig populations from several European countries [4,5]. There are two PRRSV species, Betaarterivirus suid 1 (PRRSV-1) and Betaarterivirus suid 2 (PRRSV-2), mostly widespread in Europe and North America/Asia, respectively [6,7] This virus primarily infects alveolar macrophages [8], is responsible for long-lasting infections [9,10], and is considered a causative agent of reproductive troubles, respiratory disorders and growth retardation [11]. There are three swIAV subtypes, i.e., H1N1, H1N2 and H3N2, which circulate simultaneously in areas of high pig density, with multiple region-specific genetic lineages within each subtype [14,15]. swIAV target cells are epithelial cells of the upper and lower respiratory tracts [13]. swIAV infection is responsible for acute respiratory disease, characterized by fever, cough, sneezing, apathy and dyspnea, associated with growth retardation [16]

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