Local and systemic immune response in pigs during subclinical and clinical swine influenza infection

Bacillus subtilis-597 induces changes in lung pathology and inflammation during influenza A virus infection in pigs

In recent years, it has become apparent that imbalances in the gastrointestinal system can impact organs beyond the intestine such as the lungs. Given the established ability of probiotics to modulate the immune system by interacting with gastrointestinal cells, our research aimed to investigate whether administering the probiotic strain Bacillus subtilis-597 could mitigate the outcome of influenza virus infection in pigs. Pigs were fed a diet either with or without the probiotic strain B. subtilis-597 for 14 days before being intranasally inoculated with a swine influenza A H1N2 strain (1 C.2 lineage). Throughout the study, we collected fecal samples, blood samples, and nasal swabs to examine viral shedding and immune gene expression. After seven days of infection, the pigs were euthanized, and lung and ileum tissues were collected for gene expression analysis and pathological examination. Our findings indicate that the administration of B. subtilis-597 exhibit potential in reducing lung lesions, possibly attributable to a general suppression of the immune system as indicated by reduced C-reactive protein (CRP) levels in serum, decreased expression of interferon-stimulated genes (ISGs), and localized reduction of the inflammatory marker serum amyloid A (SAA) in ileum tissue. Notably, the immune-modulatory effects of B. subtilis-597 appeared to be unrelated to the gastrointestinal microbiota, as the composition remained unaltered by both the influenza infection and the administration of B. subtilis-597.

Does Vaccine-Induced Maternally-Derived Immunity Protect Swine Offspring against Influenza a Viruses? A Systematic Review and Meta-Analysis of Challenge Trials from 1990 to May 2021

It is unclear if piglets benefit from vaccination of sows against influenza. For the first time, methods of evidence-based medicine were applied to answer the question: "Does vaccine-induced maternally-derived immunity (MDI) protect swine offspring against influenza A viruses?". Challenge trials were reviewed that were published from 1990 to April 2021 and measured at least one of six outcomes in MDI-positive versus MDI-negative offspring (hemagglutination inhibition (HI) titers, virus titers, time to begin and time to stop shedding, risk of infection, average daily gain (ADG), and coughing) (n = 15). Screening and extraction of study characteristics was conducted in duplicate by two reviewers, with data extraction and assessment for risk of bias performed by one. Homology was defined by the antigenic match of vaccine and challenge virus hemagglutinin epitopes. Results: Homologous, but not heterologous MDI, reduced virus titers in piglets. There was no difference, calculated as relative risks (RR), in infection incidence risk over the entire study period; however, infection hazard (instantaneous risk) was decreased in pigs with MDI (log HR = -0.64, 95% CI: -1.13, -0.15). Overall, pigs with MDI took about a ½ day longer to begin shedding virus post-challenge (MD = 0.51, 95% CI: 0.03, 0.99) but the hazard of infected pigs ceasing to shed was not different (log HR = 0.32, 95% CI: -0.29, 0.93). HI titers were synthesized qualitatively and although data on ADG and coughing was extracted, details were insufficient for conducting meta-analyses. Conclusion: Homology of vaccine strains with challenge viruses is an important consideration when assessing vaccine effectiveness. Herd viral dynamics are complex and may include concurrent or sequential exposures in the field. The practical significance of reduced weaned pig virus titers is, therefore, not known and evidence from challenge trials is insufficient to make inferences on the effects of MDI on incidence risk, time to begin or to cease shedding virus, coughing, and ADG. The applicability of evidence from single-strain challenge trials to field practices is limited. Despite the synthesis of six outcomes, challenge trial evidence does not support or refute vaccination of sows against influenza to protect piglets. Additional research is needed; controlled trials with multi-strain concurrent or sequential heterologous challenges have not been conducted, and sequential homologous exposure trials were rare. Consensus is also warranted on (1) the selection of core outcomes, (2) the sizing of trial populations to be reflective of field populations, (3) the reporting of antigenic characterization of vaccines, challenge viruses, and sow exposure history, and (4) on the collection of non-aggregated individual pig data.

Exploring heterologous prime-boost vaccination approaches to enhance influenza control in pigs

Influenza A viruses evolve rapidly to escape host immunity. In swine, this viral evolution has resulted in the emergence of multiple H1 and H3 influenza A virus (IAV) lineages in the United States (US) pig populations. The heterologous prime-boost vaccination strategy is a promising way to deal with diverse IAV infection in multiple animal models. However, whether or not this vaccination strategy is applicable to US swine to impart immunity against infection from North American strains of IAV is still unknown. We performed a vaccination-challenge study to evaluate the protective efficacy of using multivalent inactivated vaccine and/or a live attenuated IAV vaccine (LAIV) in pigs following multiple prime-boost vaccination protocols against a simultaneous H1N1 and H3N2 IAV infection. Our data show that pigs in the heterologous prime-boost vaccination group had more favorable outcomes consistent with a better response against virus challenge than non-vaccinated pigs. Additionally, delivering a multivalent heterologous inactivated vaccine boost to pigs following a single LAIV administration was also beneficial. We concluded the heterologous prime boost vaccination strategy may potentiate responses to suboptimal immunogens and holds the potential applicability to control IAV in the North American swine industry. However, more studies are needed to validate the application of this vaccination approach under field conditions.

Reproductive performance of pandemic influenza A virus infected sow herds before and after implementation of a vaccine against the influenza A (H1N1)pdm09 virus

Background

Reproductive failure in sow herds due to infection with influenza A viruses has been described in the literature, but only a few studies have focused on the pathogenesis and the clinical signs of the infection. Case reports indicate an association between infections with influenza A viruses and reduced reproductive performance, although it has been difficult to experimentally reproduce the clinical outcome of poor reproductive performance. The aim of the present longitudinal field study was to compare the reproductive performance parameters before and after the implementation of vaccination against the influenza A (H1N1)pdm09 virus in sow herds infected with pandemic influenza A virus. Therefore, farm-specific data of 137 sow herds in Germany, including 60,153 sows, as well as the clinical presentation of the infection were surveyed via questionnaire. Furthermore, average performance parameters (return to oestrus rate, abortion rate, stillbirth rate, number of piglets born alive per litter, preweaning mortality rate and number of piglets weaned per sow per year) were recorded for 6 months before vaccination and 6 months after completion of primary vaccination.

Results

In 79.8% of the farms, the clinical presentation of the infection was characterised by a reduced reproductive performance. These findings were confirmed by analysis of the performance parameters, which revealed a significant decline in the return to oestrus rate (p < 0.001), abortion rate (p < 0.001) and preweaning mortality rate (p = 0.023) and a significant increase of the number in piglets born alive (p = 0.001) and piglets weaned per sow per year (p < 0.001) after immunisation. The stillbirth rate did not change significantly.

Conclusion

The present study represents the first attempt to demonstrate the association of influenza A virus infection, vaccination and the alteration in reproductive performance parameters, investigating a large number of cases. The results show that by vaccinating against the influenza A (H1N1)pdm09 virus, an improvement in reproductive performance can be achieved in sow herds infected with pandemic influenza A virus. Additionally, the large number of herds that were affected by poor reproductive performance after infection with the aforementioned virus confirms the assumption of an association between pandemic influenza A virus and reproductive losses.

Co-infection of H9N2 influenza virus and Pseudomonas aeruginosa contributes to the development of hemorrhagic pneumonia in mink

Influenza A virus (IAV) and bacteria co-infection can influence the host clinical conditions. Both H9N2 IAV and Pseudomonas aeruginosa (P. aeruginosa) are potential pathogens of respiratory diseases in mink. In this study, to clarify the effects of H9N2 IAV and P. aeruginosa co-infections on hemorrhagic pneumonia in mink, we carried out to establish the mink models of the two-pathogen co-infections in different orders. Compared with the single infections with H9N2 IAV or P. aeruginosa, the mink co-infected with H9N2 IAV and P. aeruginosa showed severe respiratory diseases, and exacerbated histopathological lesions and more obvious apoptosis in the lung tissues. H9N2 IAV shedding and viral loads in the lungs of the mink co-infected with H9N2 IAV and P. aeruginosa were higher than those in the mink with single H9N2 IAV infection. Furthermore, the clearance of P. aeruginosa in the co-infected mink lungs was delayed. In addition, the anti-H9N2 antibody titers in mink with P. aeruginosa co-infection following H9N2 IAV infection were significantly higher than those of the other groups. This implied that H9N2 IAV and P. aeruginosa co-infection contributed to the development of hemorrhagic pneumonia in mink, and that P. aeruginosa should play a major role in the disease. The exact interaction mechanism among H9N2 IAV, P. aeruginosa and the host needs to be further investigated.

Potential use of hematological and acute phase protein parameters in the diagnosis of acute Schmallenberg virus infection in experimentally infected calves

The initial viraemic phase of Schmallenberg virus (SBV) infection in bovine animals is characterized by the non-specific and inconspicuous clinical signs of pyrexia (>40 °C), drop in milk yield and sometimes diarrhea. As a result, the early detection of SBV epizootics can difficult, and typically only become apparent when the congenital form of the disease is observed. The aim of the study was to describe the course of the acute phase response and haematological findings in bovine calves following experimental SBV infection. No clinical signs except for increase in rectal temperature were observed in the calves inoculated subcutaneously with a Polish strain of SBV. Viral RNA was detected in serum at 2 and 4 days post inoculation (dpi). SBV antibodies were first detected by ELISA (9-21 dpi), and subsequently by virus neutralization test (14-32 dpi). The hematological parameters showed a reduction in mid-size leucocytes (MID), and also in red blood cell count (RBC). An increase in mean corpuscular hemoglobin was also observed in SBV infected calves. No significant difference in acute phase proteins (APP) was observed between experimentally infected and control calves, suggesting limited potential as diagnostic biomarker of acute SBV infection.

Animal Models for Influenza A Virus Infection Incorporating the Involvement of Innate Host Defenses: Enhanced Translational Value of the Porcine Model

Influenza is a viral respiratory disease having a major impact on public health. Influenza A virus (IAV) usually causes mild transitory disease in humans. However, in specific groups of individuals such as severely obese, the elderly, and individuals with underlying inflammatory conditions, IAV can cause severe illness or death. In this review, relevant small and large animal models for human IAV infection, including the pig, ferret, and mouse, are discussed. The focus is on the pig as a large animal model for human IAV infection as well as on the associated innate immune response. Pigs are natural hosts for the same IAV subtypes as humans, they develop clinical disease mirroring human symptoms, they have similar lung anatomy, and their respiratory physiology and immune responses to IAV infection are remarkably similar to what is observed in humans. The pig model shows high face and target validity for human IAV infection, making it suitable for modeling many aspects of influenza, including increased risk of severe disease and impaired vaccine response due to underlying pathologies such as low-grade inflammation. Comparative analysis of proteins involved in viral pattern recognition, interferon responses, and regulation of interferon-stimulated genes reveals a significantly higher degree of similarity between pig, ferret, and human compared with mice. It is concluded that the pig is a promising animal model displaying substantial human translational value with the ability to provide essential insights into IAV infection, pathogenesis, and immunity.

Experimental infection of pigs with H1 and H3 influenza A viruses of swine by using intranasal nebulization

BACKGROUND

Experimental infection of pigs via direct intranasal or intratracheal inoculation has been mainly used to study the infectious process of influenza A viruses of swine (IAVs-S). Nebulization is known to be an alternative method for inoculating pigs with IAVs-S, because larger quantities of virus potentially can be delivered throughout the respiratory tract. However, there is very little data on the experimental infection of pigs by inhalation using nebulizer. In the current study, we used intranasal nebulization to inoculate pigs with 9 different IAVs-S-3 H1N1, 2 H1N2, and 4 H3N2 strains. We then assessed the process of infection by evaluating the clinical signs, nasal and oral viral shedding, and seroconversion rates of the pigs inoculated.

RESULTS

Lethargy and sneezing were the predominant clinical signs among pigs inoculated with 7 of the 9 strains evaluated; the remaining 2 strains (1 H1N1 and 1 H1N2 isolate) failed to induce any clinical signs throughout the experiments. Significantly increased rectal temperatures were observed with an H1N1 or H3N2 strains between 1 and 3 days post-inoculation (dpi). In addition, patterns of nasal viral shedding differed among the strains: nasal viral shedding began on 1 dpi for 6 strains, with all 9 viruses being shed from 2 to 5 dpi. The detection of viral shedding was less sensitive from oral samples than nasal secretions. Viral shedding was not detected in either nasal or oral swabs after 10 dpi. According to hemagglutination-inhibition assays, all inoculated pigs had seroconverted to the inoculating virus by 14 dpi, with titers ranging from 10 to 320.

CONCLUSIONS

Our current findings show that intranasal nebulization successfully established IAV-S infections in pigs and demonstrate that clinical signs, viral shedding, and host immune responses varied among the strains inoculated.

Coinfection modulates inflammatory responses, clinical outcome and pathogen load of H1N1 swine influenza virus and Haemophilus parasuis infections in pigs

BACKGROUND

Respiratory co-infections are important factor affecting the profitability of pigs production. Swine influenza virus (SIV) may predispose to secondary infection. Haemophilus parasuis (Hps) can be a primary pathogen or be associated with other pathogens such as SIV. To date, little is known about the effect of coinfection with SIV and Hps on the disease severity and inflammatory response and the role of Hps in the induction of pneumonia in the absence of other respiratory pathogens. In the study we investigated the influence of SIV and Hps coinfection on clinical course, inflammatory response, pathogens shedding and load at various time points following intranasal inoculation. The correlation between local concentration of cytokines and severity of disease as well as serum acute phase proteins (APP) concentration has been also studied.

RESULTS

All co-infected pigs had fever, while in single inoculated pigs fever was observed only in part of animals. Necropsy revealed lesions in the lungs all SIV-inoculated and co-inoculated pigs, while in Hps-single inoculated animals only 1 out of 11 pigs revealed gross lung lesions. The SIV shedding was the highest in co-inoculated pigs. There were no differences between Hps-single inoculated and co-inoculated groups with regard to Hps shedding. The significant increase in Hps titre in the lung has been found only in co-inoculated group. All APP increased after co-infection. In single-inoculated animals various kinetics of APP response has been observed. The lung concentrations of cytokines were induced mostly in SIV + Hps pigs in the apical and middle lobe. These results correlated well with localization of gross lung lesions.

CONCLUSIONS

The results revealed that SIV increased the severity of lung lesions and facilitated Hps (PIWetHps192/2015) replication in the porcine lung. Furthermore, Hps influenced the SIV nasal shedding. Enhanced Hps and SIV replication, together with stronger systemic and local inflammatory response contributed to a more severe clinical signs and stronger, earlier immune response in co-inoculated animals. We confirmed the previous evidence that single-Hps infection does not produce significant pneumonic lesions but it should be in mind that other strains of Hps may produce lesions different from that reported in the present study.

Pig Lung Immune Cytokine Response to the Swine Influenza Virus and the Actinobacillus Pleuropneumoniae Infection

Introduction

The aim of this study was to evaluate and compare the local innate immune response to the swine influenza virus (SIV) and Actinobacillus pleuropneumoniae (App) infection in pigs.

Material and Methods

The study was performed on 37 seven-week-old pigs, divided into four groups: App-infected (n=11), App+SIV-infected (n=11), SIV-infected (n=11), and control (n=4). Lung samples were collected, following euthanasia, on the 2^nd and 4^th dpi (three piglets per inoculated group) and on the 10^th dpi (remaining inoculated and control pigs). Lung concentrations of IL-1β, IL-6, IL-8, TNF-α, IL-10, IFN-α, and IFN-γ were analysed with the use of commercial porcine cytokine ELISA kits.

Results

Lung concentrations of IL-1β, IL-6, IL-8, TNF-α, IFN-α, and IFN-γ were induced in SIV-infected and App+SIV-infected pigs. In the lung tissue of App-infected pigs, only concentrations of IL-1β, IL-6, IL-8, and IFN-γ were elevated. Additionally, in App+SIV-infected pigs, significantly greater concentrations of IL-1β, IL-8, and IFN-α were found when compared with pigs infected with either SIV or App alone. In each tested group, the lung concentration of IL-10 remained unchanged during the entire study.

Conclusion

The results of the study indicate that the experimental infection of pigs with SIV or App alone and co-infection with both pathogens induced a local lung inflammatory response. However, the local cytokine response was considerably higher in co-infected pigs compared to single-infected pigs.

Kinetics of single and dual infection of pigs with swine influenza virus and Actinobacillus pleuropneumoniae

Porcine respiratory disease complex (PRDC) is a common problem in modern pork production worldwide. Pathogens that are amongst other pathogens frequently involved in PRDC etiology are swine influenza virus (SIV) and A. pleuropneumoniae. The effect of dual infection with mentioned pathogens has not been investigated to date. The aim of the present study was to evaluate the kinetics of single and dual infection of pigs with SIV and A. pleuropneumoniae with regard to clinical course, pathogens shedding, lung lesions and early immune response. The most severe symptoms were observed in co-inoculated piglets. The AUC value for SIV shedding was lower in pigs single inoculated with SIV as compared to co-inoculated animals. In contrast, no significant differences were found between A. pleuropneumoniae shedding in single or dual inoculated pigs. Three out of 5 co-inoculated piglets euthanized at 10 dpi were positive against serotype 2 A. pleuropneumonie. All piglets inoculated with SIV developed specific HI antibodies at 10 dpi. In pigs dual inoculated the specific humoral response against SIV was observed earlier, at 7 dpi. The SIV-like lung lesions were more severe in co-inoculated pigs. In the groups inoculated with A. pleuropneumoniae (single or dual) the acute phase protein response was generally stronger than in SIV-single infected group. Co-infection with SIV and A. pleuropneumoniae potentiated the severity of lung lesions caused by SIV and enhanced virus replication in the lung and nasal SIV shedding. Enhanced SIV replication contributed to a more severe clinical course of the disease as well as earlier and higher magnitude immune response (acute phase proteins, HI antibodies) compared to single inoculated pigs.

Distinct immune responses and virus shedding in pigs following aerosol, intra-nasal and contact infection with pandemic swine influenza A virus, A(H1N1)09

Influenza virus infection in pigs is a major farming problem, causing considerable economic loss and posing a zoonotic threat. In addition the pig is an excellent model for understanding immunity to influenza viruses as this is a natural host pathogen system. Experimentally, influenza virus is delivered to pigs intra-nasally, by intra-tracheal instillation or by aerosol, but there is little data comparing the outcome of different methods. We evaluated the shedding pattern, cytokine responses in nasal swabs and immune responses following delivery of low or high dose swine influenza pdmH1N1 virus to the respiratory tract of pigs intra-nasally or by aerosol and compared them to those induced in naturally infected contact pigs. Our data shows that natural infection by contact induces remarkably high innate and adaptive immune response, although the animals were exposed to a very low virus dose. In contacts, the kinetics of virus shedding were slow and prolonged and more similar to the low dose directly infected animals. In contrast the cytokine profile in nasal swabs, antibody and cellular immune responses of contacts more closely resemble immune responses in high dose directly inoculated animals. Consideration of these differences is important for studies of disease pathogenesis and assessment of vaccine protective efficacy.

Influenza A Virus Infection in Pigs Attracts Multifunctional and Cross-Reactive T Cells to the Lung

Pigs are natural hosts for influenza A viruses and play a critical role in influenza epidemiology. However, little is known about their influenza-evoked T-cell response. We performed a thorough analysis of both the local and systemic T-cell response in influenza virus-infected pigs, addressing kinetics and phenotype as well as multifunctionality (gamma interferon [IFN-γ], tumor necrosis factor alpha [TNF-α], and interleukin-2 [IL-2]) and cross-reactivity. A total of 31 pigs were intratracheally infected with an H1N2 swine influenza A virus (FLUAVsw) and consecutively euthanized. Lungs, tracheobronchial lymph nodes, and blood were sampled during the first 15 days postinfection (p.i.) and at 6 weeks p.i. Ex vivo flow cytometry of lung lymphocytes revealed an increase in proliferating (Ki-67(+)) CD8(+) T cells with an early effector phenotype (perforin(+) CD27(+)) at day 6 p.i. Low frequencies of influenza virus-specific IFN-γ-producing CD4(+) and CD8(+) T cells could be detected in the lung as early as 4 days p.i. On consecutive days, influenza virus-specific CD4(+) and CD8(+) T cells produced mainly IFN-γ and/or TNF-α, reaching peak frequencies around day 9 p.i., which were up to 30-fold higher in the lung than in tracheobronchial lymph nodes or blood. At 6 weeks p.i., CD4(+) and CD8(+) memory T cells had accumulated in lung tissue. These cells showed diverse cytokine profiles and in vitro reactivity against heterologous influenza virus strains, all of which supports their potential to combat heterologous influenza virus infections in pigs.

IMPORTANCE

Pigs not only are a suitable large-animal model for human influenza virus infection and vaccine development but also play a central role in the emergence of new pandemic strains. Although promising candidate universal vaccines are tested in pigs and local T cells are the major correlate of heterologous control, detailed and targeted analyses of T-cell responses at the site of infection are scarce. With the present study, we provide the first detailed characterization of magnitude, kinetics, and phenotype of specific T cells recruited to the lungs of influenza virus-infected pigs, and we could demonstrate multifunctionality, cross-reactivity, and memory formation of these cells. This, and ensuing work in the pig, will strengthen the position of this species as a large-animal model for human influenza virus infection and will immediately benefit vaccine development for improved control of influenza virus infections in pigs.

Pregnancy outcome and clinical status of gilts following experimental infection by H1N2, H3N2 and H1N1pdm09 influenza A viruses during the last month of gestation

The present study was planned to study the effect of various subtypes of swine influenza virus (SIV) circulating among pigs (H1N2, H3N2 and emerging pandemic strain of H1N1 influenza A virus (H1N1pdm09) on the course of pregnancy in naïve gilts experimentally infected during the last month of pregnancy. In addition, the clinical course of infection, distribution of viruses in various tissues (blood, placenta, fetal lung), and selected immunological, reproductive and productive parameters were also investigated. All SIV-inoculated gilts became infected. No abortions, stillbirths, intrauterine deaths or mummified fetuses were observed. No clinical signs of influenza virus infection or other disorders were observed in piglets born from infected and control gilts. There was a significant decrease in the number and frequency of lymphocytes in gilts inoculated with all influenza viruses. In general, the concentrations of IL-6, IL-10 and TNF-α were significantly higher in SIV-inoculated gilts as than in control animals, while IL-4 and IFN-γ were not detected in plasma at any time post-inoculation in SIV- or mock-inoculated gilts. No evidence for transplacental transmission of SIV was found. Viremia was also not observed in any of the infected females. On the basis of recent results, we hypothesize that pregnancy failure observed during SIV infection under field conditions is probably related to high fever and pro-inflammatory cytokines rather than a direct effect of the virus on the placenta, embryo or fetus.

Magnitude and kinetics of multifunctional CD4+ and CD8β+ T cells in pigs infected with swine influenza A virus

Although swine are natural hosts for influenza A viruses, the porcine T-cell response to swine influenza A virus (FLUAVsw) infection has been poorly characterized so far. We have studied Ki-67 expression and FLUAVsw-specific production of IFN-γ, TNF-α and IL-2 in CD4⁺ and CD8β⁺ T cells isolated from piglets that had been intratracheally infected with a H1N2 FLUAVsw isolate. IFN-γ⁺TNF-α⁺IL-2⁺ multifunctional CD4⁺ T cells were present in the blood of all infected animals at one or two weeks after primary infection and their frequency increased in four out of six animals after homologous secondary infection. These cells produced higher amounts of IFN-γ, TNF-α and IL-2 than did CD4⁺ T cells that only produced a single cytokine. The vast majority of cytokine-producing CD4⁺ T cells expressed CD8α, a marker associated with activation and memory formation in porcine CD4⁺ T cells. Analysis of CD27 expression suggested that FLUAVsw-specific CD4⁺ T cells included both central memory and effector memory populations. Three out of six animals showed a strong increase of Ki-67⁺perforin⁺ CD8β⁺ T cells in blood one week post infection. Blood-derived FLUAVsw-specific CD8β⁺ T cells could be identified after an in vitro expansion phase and were multifunctional in terms of CD107a expression and co-production of IFN-γ and TNF-α. These data show that multifunctional T cells are generated in response to FLUAVsw infection of pigs, supporting the idea that T cells contribute to the efficient control of infection.