No abstract

Pigs and humans have shared influenza A viruses (IAV) since at least 1918, and many interspecies transmission events have been documented since that time. However, despite this interplay, relatively little is known regarding IAV circulating in swine around the world compared with the avian and human knowledge base. This gap in knowledge impedes our understanding of how viruses adapted to swine or man impacts the ecology and evolution of IAV as a whole and the true impact of swine IAV on human health. The pandemic H1N1 that emerged in 2009 underscored the need for greater surveillance and sharing of data on IAV in swine. In this paper, we review the current state of IAV in swine around the world, highlight the collaboration between international organizations and a network of laboratories engaged in human and animal IAV surveillance and research, and emphasize the need to increase information in high-priority regions. The need for global integration and rapid sharing of data and resources to fight IAV in swine and other animal species is apparent, but this effort requires grassroots support from governments, practicing veterinarians and the swine industry and, ultimately, requires significant increases in funding and infrastructure.

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.

Characterisation of experimental infections of domestic pigs with genotype 2.1 and 3.3 isolates of classical swine fever virus.

Alterations of the receptor-binding properties of swine influenza A viruses (SIVs) during their isolation in embryonated chicken eggs have not been well studied. In this study, the receptorbinding properties of classical H1 SIVs isolated solely in eggs or Madin-Darby canine kidney (MDCK) cells were examined. Sequencing analysis revealed substitutions of D190V/N or D225G in the haemagglutinin (HA) proteins in egg isolates, whereas MDCK isolates retained HA genes identical to those of the original viruses present in the clinical samples. Egg isolates with substitution of either D190V/N or D225G had increased haemagglutinating activity for mouse and sheep erythrocytes, but reduced activity for rabbit erythrocytes. Additionally, egg isolates with D225G had increased haemagglutination activity for chicken erythrocytes. A direct binding assay using a sialyl glycopolymer that possessed either a 5-N-acetylneuraminic acid (Neu5Ac) a2,6galactose (Gal) or a Neu5Aca2,3Gal linkage revealed that the egg isolates used in this study showed higher binding activity to the Neu5Aca2,3Gal receptor than MDCK isolates. Increased binding activity of the egg isolates to the Neu5Aca2,3Gal receptor was also confirmed by haemagglutination assay with resialylated chicken erythrocytes by Galb1,3/4GlcNAca2,3-sialyltransferase. These observations were reinforced by flow-cytometric and N-glycan analyses of the erythrocytes. The a2,3-linked sialic acids were expressed predominantly on the surface of mouse and sheep erythrocytes. Chicken erythrocytes expressed Neu5Aca2,3Gal more abundantly than Neu5Aca2,6Gal, and rabbit erythrocytes expressed both 5-N-glycolylneuraminic acid (Neu5Gc) a2,6Gal and Neu5Aca2,6Gal. Our results demonstrate clearly that classical H1 SIVs undergo alterations in receptor-binding activity associated with an amino acid substitution in the HA protein during isolation and propagation in embryonated chicken eggs.