Role of Substitutions in the Hemagglutinin in the Emergence of the 1968 Pandemic Influenza Virus.

Hemagglutinin (HA) of H3N2/1968 pandemic influenza viruses differs from the putative avian precursor by seven amino acid substitutions. Substitutions Q226L and G228S are known to be essential for adaptation of avian HA to mammals. We found that introduction of avian-virus-like amino acids at five other HA positions (positions 62, 81, 92, 144, and 193) of A/Hong Kong/1/1968 virus decreased viral replication in human cells and transmission in pigs.

Infection of swine ex vivo tissues with avian viruses including H7N9 and correlation with glycomic analysis.

Objectives: Swine have been regarded as intermediate hosts in the spread of influenza from birds to humans but studies of the sialylated glycans that comprise their respiratory tract have not been extensively studied in the past. This study analyzed the sialylated N-glycan and O-glycan profile of swine trachea and lung and correlated this with ex-vivo infection of swine explants with avian influenza viruses.

Sample: Lungs and tracheal samples were obtained from normal farm and laboratory raised swine and used for ex vivo infection as well as mass spectrometric analysis.

Effect of receptor specificity of A/Hong Kong/1/68 (H3N2) influenza virus variants on replication and transmission in pigs.

Background: Several arguments plead for an important role of pigs in human influenza ecology, including the similar receptor expression pattern in the respiratory tract of both species. How virus receptor binding specificity affects transmission in pigs, on the other hand, has not been studied so far.

Objectives:   Using recombinant viruses R1-HK, which harbored all genes from the original pandemic virus A/Hong Kong/1/68 (H3N2), and R2-HK, which differed by L226Q and S228G mutations in the hemagglutinin and conversion to an avian-virus-like receptor specificity, we assessed the role of receptor specificity on (i) replication in porcine respiratory explants, (ii) pig-to-pig transmission, and (iii) replication and organ tropism in pigs.

Detection of highly pathogenic influenza and pandemic influenza virus in formalin fixed tissues by immunohistochemical methods.

Tissues infected with highly pathogenic avian influenza viruses such as H5N1 and H7N7 are normally required to be fixed in formalin or paraformaldehyde before examination in order to inactivate the virus. In this study commercially available monoclonal antibodies to the influenza nucleoprotein (NP) were evaluated in order to determine which antibodies would identify positive cells in tissues fixed in formalin or paraformaldehyde. An assessment of which antigen retrieval process would unmask antigens blocked by formalin fixation was also made.

Cross-protection between antigenically distinct H1N1 swine influenza viruses from Europe and North America.

Background: An avian-like H1N1 swine influenza virus (SIV) is enzootic in swine populations of Western Europe. The virus is antigenically distinct from H1N1 SIVs in North America that have a classical swine virus-lineage H1 hemagglutinin, as does the pandemic (H1N1) 2009 virus. However, the significance of this antigenic difference for cross-protection among pigs remains unknown.

Replication of avian, human and swine influenza viruses in porcine respiratory explants and association with sialic acid distribution.

Background: Throughout the history of human influenza pandemics, pigs have been considered the most likely "mixing vessel" for reassortment between human and avian influenza viruses (AIVs). However, the replication efficiencies of influenza viruses from various hosts, as well as the expression of sialic acid (Sia) receptor variants in the entire porcine respiratory tract have never been studied in detail. Therefore, we established porcine nasal, tracheal, bronchial and lung explants, which cover the entire porcine respiratory tract with maximal similarity to the in vivo situation.

Efficient transmission of swine-adapted but not wholly avian influenza viruses among pigs and from pigs to ferrets.

Background: Pigs are considered to be intermediate hosts for the transmission of avian influenza viruses (AIVs) between birds and humans, but the transmissibility of AIVs among pigs and from pigs to other mammals remains largely unexplored.

Methods: In an initial study, we confirmed the replication potential of various low-pathogenic AIVs in pigs and ferrets, which we used as a model for humans. We then examined the transmissibility of 6 selected low-pathogenic AIVs among pigs (by direct contact) and from pigs to ferrets (by air contact).