Respiratory infections are still a major concern in pigs. Amongst the involved viruses, the porcine reproductive and respiratory syndrome virus (PRRSV) and the swine influenza type A virus (swIAV) have a major impact. These viruses frequently encounter and dual infections are reported. We analyzed here the molecular interactions between viruses and porcine tracheal epithelial cells as well as lung tissue. PRRSV-1 species do not infect porcine respiratory epithelial cells. However, PRRSV-1, when inoculated simultaneously or shortly before swIAV, was able to inhibit swIAV H1N2 infection, modulate the interferon response and alter signaling protein phosphorylations (ERK, AKT, AMPK, and JAK2), in our conditions. SwIAV inhibition was also observed, although at a lower level, by inactivated PRRSV-1, whereas acid wash treatment inactivating non-penetrated viruses suppressed the interference effect. PRRSV-1 and swIAV may interact at several stages, before their attachment to the cells, when they attach to their receptors, and later on. In conclusion, we showed for the first time that PRRSV can alter the relation between swIAV and its main target cells, opening the doors to further studies on the interplay between viruses. Consequences of these peculiar interactions on viral infections and vaccinations using modified live vaccines require further investigations.

Porcine respiratory complex syndrome has a strong economic impact on the swine breeding sector, as well as a clear repercussion on the wellbeing of the animals, leading to overuse of antimicrobial molecules. Algal extracts used in short-term treatments are empirically recognized by farmers as having a positive effect on pigs’ health, however, their mechanisms of action are not well known and more research is needed. Herein we studied the short and median term impact of three algal extracts, in vitro, on the pro-inflammatory and antiviral responses of porcine primary blood monocytes and alveolar macrophages, as well as the susceptibility of the treated cells to infection by Porcine Respiratory and Reproductive Syndrome Virus (PRRSV) and the Aujeszky’s Disease Virus (ADV). All extracts presented a pro-inflammatory short-term effect, associated for two of them, with an inhibition of the PRRSV replication. Conversely, the three extracts presented an anti-inflammatory median term effect, with no impact on PRRSV replication. The observed immune modulation prompts us to test, in vivo, the anti-PRRSV action of algal extracts and strengthen the interest for this natural resource.

Bovine respiratory disease is still a major concern and has major economic impact. Another consequence of respiratory infections is the use of antimicrobial molecules to control bacterial pathogens. This can participate in the emergence and shedding of antimicrobial resistance that can threaten animal as well as human health. Appeasing pheromones with their capacity to reduce stress and thus their ability to preserve the functions of the immune system have been proposed to reduce the use of antimicrobial substances. In this study, we assessed the effect of appeasing pheromone administration on bovine health and performance during the fattening period. Zootechnical and health parameters and whole blood immune transcript expressions were measured over four weeks in bulls to determine the effect of the pheromone. We observed increased clinical signs on Day 8 (D8) and decreased clinical signs on D30 in bulls who received the pheromone and a higher expression of interleukin 8 transcripts in this group than in the control group on D8. Our results are overall in line with previous reports in livestock species. Further studies are needed to shed more light on the effect of appeasing pheromones and decipher their exact mechanisms of action.

Porcine reproductive and respiratory syndrome (PRRS) remains a major concern for the swine industry worldwide due to its significant economic impact and its association with respiratory co-infections. Vaccination is a key strategy for PRRS control; however, the most effective commercial anti-PRRSV vaccines to date—live attenuated vaccines, also named modified live virus (MLV) vaccines—provide only partial protection. This study investigates whether oral supplementation with formulated Ulva-derived seaweed extracts can enhance immune responses to PRRSV-1 MLV vaccination. Two supplementation protocols using commercial seaweed extracts formulated with vitamin A and D (Searup®) were tested: one starting one day post-vaccination for five consecutive days (post-vaccination), and another beginning one day before vaccination and continuing for two days post-vaccination (pre-vaccination). In this exploratory farm-based experimental setting, pigs were divided into six groups: three vaccinated groups (supplemented with seaweed either pre- or post-vaccination or not supplemented), and three non-vaccinated control groups receiving the same supplementation regimes. Serum cytokine levels, PRRSV viral loads, and anti-PRRSV antibody responses were measured to assess immune modulation. Post-vaccination supplementation had no significant effect on vaccine viral load or humoral response, though a modest reduction in viral persistence was noted at 12 days post-vaccination (dpv). In contrast, pre-vaccination supplementation significantly increased vaccine virus levels at 4 dpv (p = 0.048) and enhanced anti-PRRSV IgG levels (p = 0.029). This protocol also induced an early and sustained decrease in pro-inflammatory cytokines, suggesting an immunomodulatory effect of algal extract supplemented with Vitamins A and D. We present here for the first time, in field conditions and in the target species, significant immune modifications upon realistic oral supplementation with Searup®. These findings are consistent with previous studies demonstrating the potential of pre-vaccination seaweed supplementation as a cost-effective, practical strategy to enhance humoral responses to PRRSV vaccination. Further studies are needed to evaluate its impact on neutralizing antibody production, cellular responses and protection against heterologous field PRRSV strains.