Pathogenesis and inflammatory responses of swine H1N2 influenza viruses in pigs

Serological Surveillance of the H1N1 and H3N2 Swine Influenza A Virus in Chinese Swine between 2016 and 2021

Background

Swine influenza A virus (IAV-S) is a common cause of respiratory disease in pigs and poses a major public health threat. However, little attention and funding have been given to such studies. The aim of this study was to assess the prevalence of the Eurasian avian-like H1N1 (EA H1N1), 2009 pandemic H1N1 (pdm/09 H1N1), and H3N2 subtype antibodies in unvaccinated swine populations through serological investigations. Such data are helpful in understanding the prevalence of the IAV-S.

Methods

A total of 40,343 serum samples from 17 regions in China were examined using hemagglutination inhibition (HI) tests against EA H1N1, pdm/09 H1N1, and H3N2 IAV-S from 2016 to 2021. The results were analyzed based on a reginal distribution, seasonal distribution, and in different breeding stages.

Results

A total of 19,682 serum samples out of the 40,343 were positive for IAV-S (48.79%). The positivity rates to the EA H1N1 subtype, pdm/09 H1N1 subtype, and H3N2 subtype were 24.75% (9,986/40,343), 7.94% (3,205/40,343), and 0.06% (24/40,343), respectively. The occurrences of coinfections from two or more subtypes were also detected. In general, the positivity rates of serum samples were related to the regional distribution and feeding stages.

Conclusions

The results of this study showed that the anti-EA H1N1 subtype and pdm/09 H1N1 subtype antibodies were readily detected in swine serum samples. The EA H1N1 subtype has become dominant in the pig population. The occurrences of coinfections from two or more subtypes afforded opportunities for their reassortment to produce new viruses. Our findings emphasized the need for continuous surveillance of influenza viruses.

Maternal Immune Activation and Dietary Soy Isoflavone Supplementation Influence Pig Immune Function but not Muscle Fiber Formation

The goals of this study were to determine the impact of maternal PRRSV infection on offspring muscle and immune development and the potential of dietary soy isoflavones to mitigate those effects. Thirteen first-parity gilts (“gilts”) were randomly allotted into one of three treatments: not infected and fed a diet devoid of isoflavones (CON), infected with porcine reproductive and respiratory syndrome virus (PRRSV) and fed the control diet (POS) or that supplemented with 1,500 mg/kg soy-derived isoflavones (ISF). Gilts were inoculated with PRRSV intranasally on gestational day (GD) 70. After farrowing (GD 114 ± 2), 1-2 offspring (“pigs”) closest to the average litter weight were selected either at birth (3 ± 2 d of age) or weaning (21 ±2 d of age) to determine body, muscle, and organ weights as well as muscle cell number and size. Four weaned pigs of average body weight within each litter were selected for postnatal immune challenge. At PND 52, pigs were injected with 5 µg/kg BW lipopolysaccharide (LPS) intraperitoneally. Serum was collected at 0, 4, and 8 h following LPS administration to analyze tumor necrosis factor alpha (TNF-α). At PND 59, pigs were administered a novel vaccine to elicit an adaptive immune response. At PND 59, 66, and 73, peripheral blood mononuclear cells were isolated and T-cell populations determined by flow cytometry. Both POS and ISF pigs exhibited persistent PRRSV infections throughout the study (PND 1-73). At PND 3, whole body, muscle, and organ weights were not different (P > 0.22) between groups, with the exception of relative liver weight, which was increased (P < 0.05) in POS compared with CON pigs. At PND 21, ISF pigs had reduced (P ≤ 0.05) whole body and muscle weights, but greater (P < 0.05) kidney weight compared with CON, and greater (P < 0.05) relative liver weight compared with CON and POS. Muscle fiber number and size were not different (P > 0.39) between groups at birth or weaning. After LPS administration, TNF-α was greatest in ISF pigs (P < 0.05) at both 0 and 8 h post-challenge. At the peak time-point of 4 h post-challenge, ISF pigs had the greatest concentration of TNF-α and CON pigs had the lowest, with POS pigs being intermediate (P = 0.01). After vaccination, ISF offspring had shifts in T-cell populations indicating an impaired immune response. These data indicate that maternal PRRSV infection may impact offspring organ growth and immune function, particularly when the dam is supplemented with isoflavones.

Localization and immunohistochemical detection of swine influenza A virus subtype H1N1 antigen in formalin-fixed, paraffin-embedded lung tissues from naturally infected pigs

Background

Swine influenza A viruses (SIV) infection is among the leading causes of respiratory diseases in a number of animal species and human, and has been reported to cause substantial losses to pig industry. Previous reports of serological, molecular, and surveillance studies in commercial piggeries in Nigeria indicated the presence of SIV subtypes H1N1 and H3N2 in infected pigs; hitherto, there exists lack of studies on the pulmonary pathology and pathogenicity of SIV in Nigeria. This study investigates the presence of SIV subtype H1N1 antigen in the formalin-fixed paraffin-embedded lung sections obtained from apparently healthy pigs slaughtered at abattoirs located in Lagos, Ogun, and Oyo States, Southwest Nigeria using a streptavidin-biotin (ABC) immunoperoxidase (IP) staining. Two hundred four lungs consisting of 144 grossly pneumonic lungs and 60 apparently normal lungs were randomly collected, fixed in 10% neutral-buffered formalin, embedded in paraffin wax, and processed for histopathological examination and immunohistochemistry.

Results

The main gross lesions were marked pulmonary edema and mild bilateral consolidation of cranial lobes. Histopathology revealed suppurative bronchitis, and bronchiolitis with or without concurrent widespread degeneration and necrosis of epithelial cells (52.08%) and thickening of alveolar septa due to cellular infiltration consisting predominantly of neutrophils and mononuclear cells (macrophages and plasma cells) (39.58%). The lumina of most airways contained exudate consisting of neutrophils, desquamated epithelia cells, and necrotic debris. SIV antigen was immunohistochemically detected in 7/204 (3.43%) samples using SIV-specific (H1N1) monoclonal antibody. Positive cells exhibited a typical dark-brown reaction in the infected cells. A strong positive immunohistochemical staining was detected mainly in the alveolar macrophages and bronchial submucosal glandular epithelial cells while less intense staining was observed in the bronchiolar epithelial cells.

Conclusions

The present study describes the distribution and localization of SIV subtype H1N1 antigens in the lung tissues of the infected pigs and provides public awareness on the presence of the virus in pig population in Nigeria and the risk factors associated with the infection. Therefore, people working in pig farms should maintain high level of biosafety and personal hygiene. This is the first report of immunohistochemical detection of SIV subtype H1N1 antigen in naturally infected pigs in Nigeria and may indicate rapid dissemination of the virus in susceptible pigs in the study area. A further molecular epidemiological study to investigate other SIV subtypes circulating in Nigerian pig population is warranted.

Higher virulence of swine H1N2 influenza viruses containing avian-origin HA and 2009 pandemic PA and NP in pigs and mice

Pigs are capable of harbouring influenza A viruses of human and avian origin in their respiratory tracts and thus act as an important intermediary host to generate novel influenza viruses with pandemic potential by genetic reassortment between the two viruses. Here, we show that two distinct H1N2 swine influenza viruses contain avian-like or classical swine-like hemagglutinins with polymerase acidic (PA) and nucleoprotein (NP) genes from 2009 pandemic H1N1 influenza viruses that were found to be circulating in Korean pigs in 2018. Swine H1N2 influenza virus containing an avian-like hemagglutinin gene had enhanced pathogenicity, causing severe interstitial pneumonia in infected pigs and mice. The mortality rate of mice infected with swine H1N2 influenza virus containing an avian-like hemagglutinin gene was higher by 100% when compared to that of mice infected with swine H1N2 influenza virus harbouring classical swine-like hemagglutinin. Further, chemokines attracting inflammatory cells were strongly induced in lung tissues of pigs and mice infected by swine H1N2 influenza virus containing an avian-like hemagglutinin gene. In conclusion, it is necessary for the well-being of humans and pigs to closely monitor swine influenza viruses containing avian-like hemagglutinin with PA and NP genes from 2009 pandemic H1N1 influenza viruses.

Dry Taps? A Synthesis of Alternative "Wash" Methods in the Absence of Water and Sanitizers in the Prevention of Coronavirus in Low-Resource Settings

Objective: Social distancing and hand washing with soap and water have been advocated as the main proactive measures against the spread of coronavirus. We sought to find out what other alternative materials and methods would be used among populations without running water and who may not afford alcohol-based sanitizers. Results: We reviewed studies that reported use of sand, soil, ash, soda ash, seawater, alkaline materials, and sunlight as possible alternatives to handwashing with soap and water. We identified the documented mechanism of actions of these alternative wash methods on both inanimate surfaces and at cellular levels. The consideration of use of these alternative locally available in situations of unavailability of soap and water and alcohol-based sanitizers is timely in the face of coronavirus pandemic. Further randomized studies need to be carried out to evaluate the effectiveness of these alternatives in management of SARS-Cov-2.

Liposomal nanoparticle-based conserved peptide influenza vaccine and monosodium urate crystal adjuvant elicit protective immune response in pigs

Background

Influenza (flu) is a constant threat to humans and animals, and vaccination is one of the most effective ways to mitigate the disease. Due to incomplete protection induced by current flu vaccines, development of novel flu vaccine candidates is warranted to achieve greater efficacy against constantly evolving flu viruses.

Methods

In the present study, we used liposome nanoparticle (<200 nm diameter)-based subunit flu vaccine containing ten encapsulated highly conserved B and T cell epitope peptides to induce protective immune response against a zoonotic swine influenza A virus (SwIAV) H1N1 challenge infection in a pig model. Furthermore, we used monosodium urate (MSU) crystals as an adjuvant and co-administered the vaccine formulation as an intranasal mist to flu-free nursery pigs, twice at 3-week intervals.

Results

Liposome peptides flu vaccine delivered with MSU adjuvant improved the hemagglutination inhibition antibody titer and mucosal IgA response against the SwIAV challenge and also against two other highly genetically variant IAVs. Liposomal vaccines also enhanced the frequency of peptides and virus-specific T-helper/memory cells and IFN-γ response. The improved specific cellular and mucosal humoral immune responses in adjuvanted liposomal peptides flu vaccine partially protected pigs from flu-induced fever and pneumonic lesions, and reduced the nasal virus shedding and viral load in the lungs.

Conclusion

Overall, our study shows great promise for using liposome and MSU adjuvant- based subunit flu vaccine through the intranasal route, and provides scope for future, pre-clinical investigations in a pig model for developing potent human intranasal subunit flu vaccines.

Mycoplasma hyopneumoniae does not affect the interferon-related anti-viral response but predisposes the pig to a higher level of inflammation following swine influenza virus infection

In pigs, influenza A viruses and Mycoplasma hyopneumoniae (Mhp) are major contributors to the porcine respiratory disease complex. Pre-infection with Mhp was previously shown experimentally to exacerbate the clinical outcomes of H1N1 infection during the first week after virus inoculation. In order to better understand the interactions between these pathogens, we aimed to assess very early responses (at 5, 24 and 48 h) after H1N1 infection in pigs pre-infected or not with Mhp. Clinical signs and macroscopic lung lesions were similar in both infected groups at early times post-H1N1 infection; and Mhp pre-infection affected neither the influenza virus replication nor the IFN-induced antiviral responses in the lung. However, it predisposed the animals to a higher inflammatory response to H1N1 infection, as revealed by the massive infiltration of neutrophils and macrophages into the lungs and the increased production of pro-inflammatory cytokines (IL-6, IL-1β and TNF-α). Thus, it seems it is this marked inflammatory state that would play a role in exacerbating the clinical signs subsequent to H1N1 infection.

Integrative analysis of differentially expressed microRNAs of pulmonary alveolar macrophages from piglets during H1N1 swine influenza A virus infection

H1N1 swine influenza A virus (H1N1 SwIV) is one key subtype of influenza viruses with pandemic potential. MicroRNAs (miRNAs) are endogenous small RNA molecules that regulate gene expression. MiRNAs relevant with H1N1 SwIV have rarely been reported. To understand the biological functions of miRNAs during H1N1 SwIV infection, this study profiled differentially expressed (DE) miRNAs in pulmonary alveolar macrophages from piglets during the H1N1 SwIV infection using a deep sequencing approach, which was validated by quantitative real-time PCR. Compared to control group, 70 and 16 DE miRNAs were respectively identified on post-infection day (PID) 4 and PID 7. 56 DE miRNAs were identified between PID 4 and PID 7. Our results suggest that most host miRNAs are down-regulated to defend the H1N1 SwIV infection during the acute phase of swine influenza whereas their expression levels gradually return to normal during the recovery phase to avoid the occurrence of too severe porcine lung damage. In addition, targets of DE miRNAs were also obtained, for which bioinformatics analyses were performed. Our results would be useful for investigating the functions and regulatory mechanisms of miRNAs in human influenza because pig serves as an excellent animal model to study the pathogenesis of human influenza.

Comparative pathology of pigs infected with Korean H1N1, H1N2, or H3N2 swine influenza A viruses

Background

The predominant subtypes of swine influenza A virus (SIV) in Korea swine population are H1N1, H1N2, and H3N2. The viruses are genetically close to the classical U.S. H1N1 and triple-reassortant H1N2 and H3N2 viruses, respectively. Comparative pathogenesis caused by Korean H1N1, H1N2, and H3N2 SIV was evaluated in this study.

Findings

The H3N2 infected pigs had severe scores of gross and histopathological lesions at post-inoculation days (PID) 2, and this then progressively decreased. Both the H1N1 and H1N2 infected pigs lacked gross lesions at PID 2, but they showed moderate to severe pneumonia on PID 4, 7 and 14. The pigs infected with H1N1 had significant scores of gross and histopathological lesions when compared with the other pigs infected with H1N2, H3N2, and mock at PID 14. Mean SIV antigen-positive scores were rarely detected for pigs infected with H1N2 and H3N2 from PID 7, whereas a significantly increased amount of viral antigens were found in the bronchioles and alveolar epithelium of the H1N1infected pigs at PID 14.

Conclusions

We demonstrated that Korean SIV subtypes had different pulmonary pathologic patterns. The Korean H3N2 rapidly induced acute lung lesions such as broncho-interstitial pneumonia, while the Korean H1N1 showed longer course of infection as compared to other strains.

A novel reassortant H1N2 virus related to the pandemic H1N1 2009 influenza virus isolated from Korean pigs

Since the discovery of the pandemic H1N1 (pH1N1) virus in 2009, a novel reassortant H1N2 virus (A/Swine/Korea/VDS1/2010) containing the pH1N1 segments has been detected in Korean pig populations. The hemagglutinin and neuraminidase genes of this virus are derived from reassortant H1N1- and H1N2-group viruses, respectively, identified in Korean pigs, while other genes originate from contemporary circulating pH1N1 viruses. The antigenic and biological properties of this novel virus, as determined by clinical, pathological, serological, and genetic analyses, are similar to those of pH1N1 viruses, which infect swine easily (Weingartl et al. J Virol 84:2245-2256, 2010; Brookes et al. PLoS one 5:e9068, 2010; Lange et al. J Gen Virol 90:2119-2123, 2009). Determining whether this virus will become established and pose a threat to mammalian populations requires further investigation.

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

Local and systemic immune responses in pigs intranasally (IN) and intratracheally (IT) inoculated with swine influenza virus (SIV) were studied. No clinical signs were observed in IN-inoculated pigs, while IT-inoculated pigs developed typical signs of influenza. Significantly higher titres of specific antibodies and changes of haematological parameters were found only in IT-inoculated pigs. Because positive correlations between viral titre, local cytokine concentration, and lung pathology have been observed, we hypothesise that both viral load and the local secretion of cytokines play a role in the induction of lung lesions. It could be that a higher replication of SIV stimulates immune cells to secrete higher amounts of cytokines. The results of the present study indicate that pathogenesis of SIV is dependent on both, the damage caused to the lung parenchyma directly by virus, and the effects on the cells of the host's immune system.

Immune and inflammatory response in pigs during acute influenza caused by H1N1 swine influenza virus

Swine influenza (SI) is an acute respiratory disease of pigs, caused by swine influenza virus (SIV). Little is known about the inflammatory response in the lung during acute SI and its correlation with clinical signs or lung pathology. Moreover, until now there has been a limited amount of data available on the relationship between the concentrations of pro- and anti-inflammatory cytokines in the lungs and the serum concentration of acute-phase proteins (APPs) in SIV-infected pigs. In the present study, the porcine inflammatory and immune responses during acute influenza caused by H1N1 SIV (SwH1N1) were studied. Nine pigs were infected intratracheally, and five served as controls. Antibodies against SIV were measured by haemagglutination inhibition assay, and the influenza-virus-specific T-cell response was measured using a proliferation assay. C-reactive protein (CRP), haptoglobin (Hp), serum amyloid A (SAA), and pig major acute-phase protein (Pig-MAP) the concentrations in serum and concentration of IL-1β, IL-6, IL-8, IL-10, TNF-α and IFN-γ in lung tissues were measured using commercial ELISAs.

Antibody and inflammatory response-mediated severity of pandemic 2009 (pH1N1) influenza virus

Influenza A virus causes significant morbidity and mortality each year worldwide due to antigenic drift, punctuated by infrequent pandemics following antigenic shift. H1N1 subtype of pandemic 2009 (pH1N1) influenza virus lineages has continued to circulate in humans and raised severe concerns about its pandemic developments. The pathogenesis of the disease and its progression as post-infectious sequelae is not well understood. Moderate inflammatory response protects against the ill effects and hyper-inflammatory response promotes the pathogenesis in disease progression. Samples were screened by RT-PCR and classified in pandemic 2009 (pH1N1), Influenza A virus infected patient. Further antibody titer was analyzed by hemagglutination inhibition assay and cytokine/chemokine response by Cytometric bead array assy. Screening of 216 patients shows 63 were belongs to pH1N1 influenza virus infection and 47 were Influenza A virus infected and 106 samples were negative for these viruses, were used as a disease control. Apart from that 100 samples were taken for healthy control. Lower antibody titer was found in patient infected with pH1N1/Influenza A virus and expression of cytokines (IL-6, IL-8, and IL-10) and chemokine MCP-1 was higher in patient infected with pH1N1 compare to healthy/disease control however there was no significant difference observed in the expression of pro-inflammatory cytokines TNF-α and antiviral cytokine IFN-γ in pH1N1 influenza virus infected patients.

Cytokine and chemokine mRNA expression profiles in BALF cells isolated from pigs single infected or co-infected with swine influenza virus and Bordetella bronchiseptica

Pigs serve as a valuable animal experimental model for several respiratory pathogens, including Swine Influenza Virus (SIV) and Bordetella bronchiseptica (Bbr). To investigate the effect of SIV and Bbr coinfection on cytokine and viral RNA expression, we performed a study in which pigs were inoculated with SIV, Bbr or both pathogens (SIV/Bbr). Our results indicate that Bbr infection alters SIV clearance. Pulmonary lesions in the SIV/Bbr group were more severe when compared to SIV or Bbr groups and Bbr did not cause significant lesions. Broncho-alveolar lavage fluid (BALF) was examined for inflammatory mediators by qPCR. Interferon (IFN)-α, interleukin IL-8, IL-1 peaked in BALF at 2 DPI, while the virus titres and severity of clinical signs were maximal at the same time. Despite its increased expression in co-infected pigs, interferon-α did not enhance SIV clearance, since the viral replication was detected at the same day as the highest IFN levels. The mRNA levels for IFN-α, IL-1β and IL-8 were significantly higher in BALF of co-infected pigs and correlated with enhanced viral RNA titers in lungs, trachea and nasal swabs. Transcription of mRNA for IL-1β was stable in SIV and SIV/Bbr groups throughout all the study. In Bbr group, the levels of mRNAs for IL-1β were significantly higher at 2, 4 and 9 DPI. The mean levels of mRNAs for TNF-α were lower than the levels of other chemokines and cytokines in all infected groups. Transcript levels of IL-10 and IL-4 did not increase at each time points. Overall, SIV replication was increased by Bbr presence and the enhanced production of pro-inflammatory mediators could contribute to the exacerbated pulmonary lesions.

Pathogenesis and vaccination of influenza A virus in swine

Swine influenza is an acute respiratory disease of pigs caused by influenza A virus (IAV) and characterized by fever followed by lethargy, anorexia, and serous nasal discharge. The disease progresses rapidly and may be complicated when associated with other respiratory pathogens. IAV is one of the most prevalent respiratory pathogens of swine, resulting in substantial economic burden to pork producers. In the past 10-15 years, a dramatic evolution of the IAV in U.S. swine has occurred, resulting in the co-circulation of many antigenically distinct IAV strains, derived from 13 phylogenetically distinct hemagglutinin clusters of H1 and H3 viruses. Vaccination is the most common strategy to prevent influenza in pigs, however, the current diverse IAV epidemiology poses a challenge for the production of efficacious and protective vaccines. A concern regarding the use of traditional inactivated vaccines is the possibility of inducing vaccine-associated enhanced respiratory disease (VAERD) when vaccine virus strains are mismatched with the infecting strain. In this review, we discuss the current epidemiology and pathogenesis of swine influenza in the United States, different vaccines platforms with potential to control influenza in pigs, and the factors associated with vaccine-associated disease enhancement.

Influenza A virus infections in swine: pathogenesis and diagnosis

Influenza has been recognized as a respiratory disease in swine since its first appearance concurrent with the 1918 "Spanish flu" human pandemic. All influenza viruses of significance in swine are type A, subtype H1N1, H1N2, or H3N2 viruses. Influenza viruses infect epithelial cells lining the surface of the respiratory tract, inducing prominent necrotizing bronchitis and bronchiolitis and variable interstitial pneumonia. Cell death is due to direct virus infection and to insult directed by leukocytes and cytokines of the innate immune system. The most virulent viruses consistently express the following characteristics of infection: (1) higher or more prolonged virus replication, (2) excessive cytokine induction, and (3) replication in the lower respiratory tract. Nearly all the viral proteins contribute to virulence. Pigs are susceptible to infection with both human and avian viruses, which often results in gene reassortment between these viruses and endemic swine viruses. The receptors on the epithelial cells lining the respiratory tract are major determinants of infection by influenza viruses from other hosts. The polymerases, especially PB2, also influence cross-species infection. Methods of diagnosis and characterization of influenza viruses that infect swine have improved over the years, driven both by the availability of new technologies and by the necessity of keeping up with changes in the virus. Testing of oral fluids from pigs for virus and antibody is a recent development that allows efficient sampling of large numbers of animals.

Genetic characterization of H1N2 swine influenza virus isolated in China and its pathogenesis and inflammatory responses in mice

In 2009, two H1N2 influenza viruses were isolated from trachea swabs of pigs in Hubei in China. We compared these sequences with the other 18 complete genome sequences of swine H1N2 isolates from China during 2004 to 2010 and undertook extensive analysis of their evolutionary patterns. Six different genotypes - two reassortants between triple reassortant (TR) H3N2 and classical swine (CS) H1N1 virus, three reassortants between TR H1N2, Eurasian avian-like H1N1 swine virus and H9N2 swine virus, and one reassortant between H1N1, H3N2 human virus and CS H1N1 virus - were observed in these 20 swine H1N2 isolates. The TR H1N2 swine virus is the predominant genotype, and the two Hubei H1N2 isolates were located in this cluster. We also used a mouse model to examine the pathogenesis and inflammatory responses of the two isolates. The isolates replicated efficiently in the lung, and exhibited a strong inflammatory response, serious pathological changes and mortality in infected mice. Given the role that swine can play as putative "genetic mixing vessels" and the observed transmission of TR H1N2 in ferrets, H1N2 influenza surveillance in pigs should be increased to minimize the potential threat to public health.

Expression of innate immune genes, proteins and microRNAs in lung tissue of pigs infected experimentally with influenza virus (H1N2)

This study aimed at providing a better understanding of the involvement of innate immune factors, including miRNA, in the local host response to influenza virus infection. Twenty pigs were challenged by influenza A virus subtype H1N2. Expression of microRNA (miRNA), mRNA and proteins were quantified in lung tissue at different time points after challenge (24 h, 72 h and 14 d post-infection (p.i.). Several groups of genes were significantly regulated according to time point and infection status including pattern recognition receptors (TLR2, TLR3, TLR7, retinoic acid-inducible gene I, melanoma differentiation associated protein-5), IFN and IFN-induced genes (IFN-β, IFN-γ, IRF7, STAT1, ISG15 and OASL), cytokines (IL-1 β, IL-1RN, IL-6, IL-7, IL-10, IL-12A, TNF-α, CCL2, CCL3 and CXCL10) and several acute phase proteins. Likewise, the following miRNAs were differentially expressed in one or more time groups compared with the control pigs: miR-15a, miR-21, miR-146, miR-206, miR-223 and miR-451. At d 1 p.i. lung tissue protein levels of IL-6, IL-12 and IFN-α were significantly increased compared with the control group, and haptoglobin and C-reactive protein were significantly increased at d 3 p.i. Our results suggest that, in addition to a wide range of innate immune factors, miRNAs may also be involved in controlling acute influenza infection in pigs.

Theoretical investigation on the binding specificity of sialyldisaccharides with hemagglutinins of influenza A virus by molecular dynamics simulations

Recognition of cell-surface sialyldisaccharides by influenza A hemagglutinin (HA) triggers the infection process of influenza. The changes in glycosidic torsional linkage and the receptor conformations may alter the binding specificity of HAs to the sialylglycans. In this study, 10-ns molecular dynamics simulations were carried out to examine the structural and dynamic behavior of the HAs bound with sialyldisaccharides Neu5Acα(2-3)Gal (N23G) and Neu5Acα(2-6)Gal (N26G). The analysis of the glycosidic torsional angles and the pair interaction energy between the receptor and the interacting residues of the binding site reveal that N23G has two binding modes for H1 and H5 and a single binding mode for H3 and H9. For N26G, H1 and H3 has two binding modes, and H5 and H9 has a single binding mode. The direct and water-mediated hydrogen bonding interactions between the receptors and HAs play dominant roles in the structural stabilization of the complexes. It is concluded from pair interaction energy and Molecular Mechanic-Poisson-Boltzmann Surface Area calculations that N26G is a better receptor for H1 when compared with N23G. N23G is a better receptor for H5 when compared with N26G. However, H3 and H9 can recognize N23G and N26G in equal binding specificity due to the marginal energy difference (≈2.5 kcal/mol). The order of binding specificity of N23G is H3 > H5 > H9 > H1 and N26G is H1 > H3 > H5 > H9, respectively. The proposed conformational models will be helpful in designing inhibitors for influenza virus.

Pre-infection of pigs with Mycoplasma hyopneumoniae modifies outcomes of infection with European swine influenza virus of H1N1, but not H1N2, subtype

Swine influenza virus (SIV) and Mycoplasma hyopneumoniae (Mhp) are widespread in farms and are major pathogens involved in the porcine respiratory disease complex (PRDC). The aim of this experiment was to compare the pathogenicity of European avian-like swine H1N1 and European human-like reassortant swine H1N2 viruses in naïve pigs and in pigs previously infected with Mhp. Six groups of SPF pigs were inoculated intra-tracheally with either Mhp, or H1N1, or H1N2 or Mhp + H1N1 or Mhp + H1N2, both pathogens being inoculated at 21 days intervals in these two last groups. A mock-infected group was included. Although both SIV strains induced clinical signs when singly inoculated, results indicated that the H1N2 SIV was more pathogenic than the H1N1 virus, with an earlier shedding and a greater spread in lungs. Initial infection with Mhp before SIV inoculation increased flu clinical signs and pathogenesis (hyperthermia, loss of appetite, pneumonia lesions) due to the H1N1 virus but did not modify significantly outcomes of H1N2 infection. Thus, Mhp and SIV H1N1 appeared to act synergistically, whereas Mhp and SIV H1N2 would compete, as H1N2 infection led to the elimination of Mhp in lung diaphragmatic lobes. In conclusion, SIV would be a risk factor for the severity of respiratory disorders when associated with Mhp, depending on the viral subtype involved. This experimental model of coinfection with Mhp and avian-like swine H1N1 is a relevant tool for studying the pathogenesis of SIV-associated PRDC and testing intervention strategies for the control of the disease.

Transcription analysis on response of swine lung to H1N1 swine influenza virus

BACKGROUND

As a mild, highly contagious, respiratory disease, swine influenza always damages the innate immune systems, and increases susceptibility to secondary infections which results in considerable morbidity and mortality in pigs. Nevertheless, the systematical host response of pigs to swine influenza virus infection remains largely unknown. To explore it, a time-course gene expression profiling was performed for comprehensive analysis of the global host response induced by H1N1 swine influenza virus in pigs.

RESULTS

At the early stage of H1N1 swine virus infection, pigs were suffering mild respiratory symptoms and pathological changes. A total of 268 porcine genes showing differential expression (DE) after inoculation were identified to compare with the controls on day 3 post infection (PID) (Fold change ≥ 2, p < 0.05). The DE genes were involved in many vital functional classes, mainly including signal transduction, immune response, inflammatory response, cell adhesion and cell-cell signalling. Noticeably, the genes associated with immune and inflammatory response showed highly overexpressed. Through the pathway analysis, the significant pathways mainly concerned with Cell adhesion molecules, Cytokine-cytokine receptor interaction, Toll-like receptor signaling pathway and MAPK signaling pathway, suggesting that the host took different strategies to activate these pathways so as to prevent virus infections at the early stage. However, on PID 7, the predominant function classes of DE genes included signal transduction, metabolism, transcription, development and transport. Furthermore, the most significant pathways switched to PPAR signaling pathway and complement and coagulation cascades, showing that the host might start to repair excessive tissue damage by anti-inflammatory functions. These results on PID 7 demonstrated beneficial turnover for host to prevent excessive inflammatory damage and recover the normal state by activating these clusters of genes.

CONCLUSIONS

This study shows how the target organ responds to H1N1 swine influenza virus infection in pigs. The observed gene expression profile could help to screen the potential host agents for reducing the prevalence of swine influenza virus and further understand the molecular pathogenesis associated with H1N1 infection in pigs.

Genetic diversity of swine influenza viruses isolated from pigs during 2000 to 2005 in Thailand

Background  Recent studies have revealed the existence of genetic diversity in swine influenza viruses (SIVs) in the world. In Thailand, there has been a little information on the molecular characteristics of the SIVs since the first isolation of viruses of H1N1 and H3N2 subtypes in the late 1970s. Our previous study demonstrated that Thai H1N1 SIVs possessed the classical swine H1 and avian‐like swine N1 genes (Takemae et al., Proceedings of the Options for the Control of Influenza VI.2007;350–353).

Objectives  In the present study, we genetically characterized 12 SIVs including those of H1N1, H1N2 and H3N2 subtypes isolated between 2000 and 2005.

Methods  We determined the entire nucleotide sequences of the eight gene segments of those isolates.

Results  Phylogenetic analysis revealed the existence of nine distinct genotypes amongst the Thai SIVs. These genotypes arose from multiple introductions of classical swine, avian‐like swine and human viruses. The existence of two distinct sublineages within classical swine H1 and NS, avian‐like swine PA and M and human H3 and N2 genes of the Thai SIVs suggested that introduction of viruses of classical swine, avian‐like swine and human origins occurred twice respectively into the Thai pig population. The predominance of avian‐like swine genes amongst the Thai SIVs was evident. In particular, three polymerase (PB1, PB2 and PA) and matrix genes of avian‐like swine origin were retained in all the Thai SIVs examined.

Conclusions  These observations may suggest that genes of avian‐like swine lineages have some advantages to be maintained in pigs as seen in the SIVs established through multiple introductions in other regions.