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Introduction The lack of proofreading activity of the viral polymerase and the segmented nature of the influenza A virus (IAV) genome are responsible for the genetic diversity of IAVs and for their ability to adapt to a new host. We tried to adapt avian IAV (avIAV) to the pig by serial passages in vivo and assessed the occurrence of point mutations and their influence on viral fitness in the pig’s body. Material and Methods A total of 25 in vivo avIAV passages of the A/duck/Bavaria/77 strain were performed by inoculation of 50 piglets, and after predetermined numbers of passages 20 uninoculated piglets were exposed to the virus through contact with inoculated animals. Clinical signs of swine influenza were assessed daily. Nasal swabs and lung tissue were used to detect IAV RNA by real-time RT-PCR and isolates from selected passages were sequenced. Results Apart from a rise in rectal temperature and a sporadic cough, no typical clinical signs were observed in infected pigs. The original strain required 20 passages to improve its replication ability noticeably. A total of 29 amino-acid substitutions were identified. Eighteen of them were detected in the first sequenced isolate, of which 16 were also in all other analysed strains. Additional mutations were detected with more passages. One substitution, threonine (T) 135 to serine (S) in neuraminidase (NA), was only detected in an IAV isolate from a contact-exposed piglet. Conclusion Passaging 25 times allowed us to obtain a partially swine-adapted IAV. The improvement in isolate replication ability was most likely related to S654 to glycine (G) substitution in the basic protein (PB) 1 as well as to aspartic acid (D) 701 to asparagine (N) and arginine (R) 477 to G in PB2, glutamic acid (E) 204 to D and G239E in haemagglutinin and T135S in NA.

The aim of the study was to monitor genetic diversity and antigenic changes in the genome of influenza A(H1N1)pdm09 viral isolates detected during the post-pandemic period in Poland. Clinical specimens obtained from three suspected cases of influenza were analysed by sequencing. Among the differences identified in amino acids sequences, nine substitutions were located within the antigenic HA1 sites and in five residues forming receptor-binding pocket. The HA(D222G) mutation was shown in the isolate Swine/Poland/134312/12 obtained from a mild case of the disease. It must be emphasized that, in general, clinically mild cases are caused by the viruses in which that specific mutation, i.e. haemagglutinin (D222G), does not occur.

The kinetics of C-reactive protein (CRP), haptoglobin (Hp), serum amyloid A (SAA), and pig major acute protein (Pig-MAP) response in pigs co-infected with H3N2 swine influenza virus (SwH3N2) and Bordetella bronchiseptica (Bbr) was studied, with assessment of potential correlations between the concentration of acute phase proteins (APPs) in serum samples, lung lesions, and the clinical course of the disease in co-infected pigs. The standard bacteriological methods for detection of Bbr and PCR technique for identification of Bbr and SwH3N2 were used. The serum concentrations of APPs were measured using ELISA. The concentration of CRP, SAA, and Pig-MAP was significantly higher from 2 to 4 or 5 dpi. The concentration of Hp was elevated until the end of the study. Significant correlations were found between the serum concentration of SAA and Pig-MAP and clinical score, and between the concentration of SAA and lung score. Apart from their potential as biological markers for co-infections, SAA and Pig-MAP levels have additive value since they are related to the severity of infection. The results indicate that measurement of APP (i.e SAA) may prove valuable in assessing the severity of respiratory infection in pigs, and may be of supportive value in the clinical evaluation of animals and in the selection of more appropriate treatment.

The outbreaks of pandemic H1N1 influenza A virus (pdm-like H1N1 2009), detected for the first time in farrow-to-finish farms in Poland, were described. The nasal swabs and lung tissue collected from diseased/dead animals were tested using molecular techniques (RRT-PCR, MRT-PCR, RT-PCR, SSG-PCR, sequencing) and virus isolation. The amplification of the genetic material extracted from the tested samples confirmed the presence of the M1 gene sequence of type A influenza virus. Using MRT-PCRs no products characteristic for HA and NA of any swine influenza virus subtypes were obtained. Using SSGPCR, products specific for pandemic HA and NA gene fragments were detected. Six new pdm-like H1N1 2009 strains were isolated and characterised. Phylogenetic analysis of the HA and NA genes revealed that they belong to one lineage with the pandemic strain A/California/04/2009 and other human strains, including human strains isolated in Poland in 2011.

The paper describes an outbreak of swine influenza, which was the first H1N2 outbreak confirmed in pig farm in Poland. The outbreak occurred in October 2011 in the farrows to finish farm, first in the fattening units, and subsequently in the reproduction and weaning sectors. Samples of the lungs taken from dead gilts were tested by the use of real time and multiplex PCR, sequencing, and virus isolation methods. The amplification of the genetic material extracted from the lungs confirmed the presence of the M1 gene sequence of type A influenza virus. Using multiplex PCR, the bands of 241 bp, typical for HA1 human-like type, and of 791 bp, typical for NA2, were demonstrated. The new isolates of swine influenza virus, named A/swine/Poland/15817/2011, were obtained in embryonated SPF chicken eggs and MDCK cells. Phylogenetic analysis of the HA and NA genes of the isolate revealed that the virus is of human swine linkage closely related to European human-like viruses. On the basis of such results, it can be stated that A/Swine/Poland/15817/2011 is a new swine influenza virus, representing the H1N2 subtype strain, which emerged in Poland.