Mutations in the Neuraminidase-Like Protein of Bat Influenza H18N11 Virus Enhance Virus Replication in Mammalian Cells, Mice, and Ferrets.

To characterize bat influenza H18N11 virus, we propagated a reverse genetics-generated H18N11 virus in Madin-Darby canine kidney subclone II cells and detected two mammal-adapting mutations in the neuraminidase (NA)-like protein (NA-F144C and NA-T342A, N2 numbering) that increased the virus titers in three mammalian cell lines (i.e., Madin-Darby canine kidney, Madin-Darby canine kidney subclone II, and human lung adenocarcinoma [Calu-3] cells).

Differentiated swine airway epithelial cell cultures for the investigation of influenza A virus infection and replication.

Background: Differentiated human airway epithelial cell cultures have been utilized to investigate cystic fibrosis, wound healing, and characteristics of viral infections. These cultures, grown at an air-liquid interface (ALI) in media with defined hormones and growth factors, recapitulate many aspects of the in vivo respiratory tract and allow for experimental studies at the cellular level.

Objectives: To optimize growth conditions for differentiated swine airway epithelial cultures and to use these cultures to examine influenza virus infection and replication.

Infectivity phenotypes of H3N2 influenza A viruses in primary swine respiratory epithelial cells are controlled by sialic acid binding.

Background: In the late 1990s, triple reassortant H3N2 influenza A viruses emerged and spread widely in the US swine population. We have shown previously that an isolate representative of this virus-lineage, A/Swine/Minnesota/593/99 (Sw/MN), exhibits phenotypic differences compared to a wholly human-lineage H3N2 virus isolated during the same time period, A/Swine/Ontario/00130/97 (Sw/ONT). Specifically, Sw/MN was more infectious for pigs and infected a significantly higher proportion of cultured primary swine respiratory epithelial cells (SRECs).

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.

Transmission of influenza A viruses between pigs and people, Iowa, 2002-2004.

Background: Triple-reassortant (tr) viruses of human, avian, and swine origin, including H1N1, H1N2, and H3N2 subtypes, emerged in North American swine herds in 1998 and have become predominant. While sporadic human infections with classical influenza A (H1N1) and with tr-swine influenza viruses have been reported, relatively few have been documented in occupationally exposed swine workers (SW).

Methods: We conducted a 2-year (2002-2004) prospective cohort study of transmission of influenza viruses between pigs and SW from a single pork production company in Iowa.

Maternal influenza infection during pregnancy impacts postnatal brain development in the rhesus monkey.

Background: Maternal infection with influenza and other pathogens during pregnancy has been associated with increased risk for schizophrenia and neurodevelopmental disorders. In rodent studies, maternal inflammatory responses to influenza affect fetal brain development. However, to verify the relevance of these findings to humans, research is needed in a primate species with more advanced prenatal corticogenesis.

Amino acid 226 in the hemagglutinin of H4N6 influenza virus determines binding affinity for alpha2,6-linked sialic acid and infectivity levels in primary swine and human respiratory epithelial cells.

Avian lineage H4N6 influenza viruses previously isolated from pigs differ at hemagglutinin amino acids 226 and 228 from H4 subtype viruses isolated from birds. Using a parental H4N6 swine isolate and hemagglutinin mutant viruses (at residues 226 and/or 228), we determined that viruses which contain L226 had a higher affinity for sialic acid alpha2,6 galactose (SAalpha2,6Gal) and a higher infectivity level for primary swine and human respiratory epithelial cells, whereas viruses which contain Q226 had lower SAalpha2,6Gal affinity and lower infectivity levels for both types of cells. Using specific neuraminidases, we found that irrespective of their relative binding preferences, all of the influenza viruses examined utilized SAalpha2,6Gal to infect swine and human cells.

Identification of amino acids in the HA of H3 influenza viruses that determine infectivity levels in primary swine respiratory epithelial cells.

In the late 1990s, triple reassortant H3N2 influenza A viruses emerged and spread widely within the swine population of the United States. We have shown previously that an isolate representative of this lineage of viruses, A/Swine/Minnesota/593/99 (Sw/MN), has higher infectivity and accelerated replication kinetics in pigs, compared to a human-lineage H3N2 virus isolated from a pig during the same time period, A/Swine/Ontario/00130/97 (Sw/ONT [Landolt, G.A.

Triple reassortant H3N2 influenza A viruses, Canada, 2005.

Since January 2005, H3N2 influenza viruses have been isolated from pigs and turkeys throughout Canada and from a swine farmer and pigs on the same farm in Ontario. These are human/classical swine/avian reassortants similar to viruses that emerged in US pigs in 1998 but with a distinct human-lineage neuraminidase gene.

Identification of human H1N2 and human-swine reassortant H1N2 and H1N1 influenza A viruses among pigs in Ontario, Canada (2003 to 2005).

Since 2003, three novel genotypes of H1 influenza viruses have been recovered from Canadian pigs, including a wholly human H1N2 virus and human-swine reassortants. These isolates demonstrate that human-lineage H1N2 viruses are infectious for pigs and that viruses with a human PB1/swine PA/swine PB2 polymerase complex can replicate in pigs.

Restricted infectivity of a human-Lineage H3N2 influenza A virus in pigs is hemagglutinin and neuraminidase gene dependent.

Influenza A viruses cause pandemics at sporadic intervals. Pandemic viruses can potentially be introduced into the human population through in toto transfer of an avian influenza virus or through reassortment between avian and human strains. Pigs are believed to play a central role in the creation of pandemic viruses through reassortment because of their susceptibility to infection with both avian and human influenza viruses.

Receptor-binding properties of swine influenza viruses isolated and propagated in MDCK cells.

To study the receptor specificities of H1 and H3 influenza viruses isolated recently from pigs, we employed the analogues of natural receptors, namely sialyloligosaccharides conjugated with polyacrylamide in biotinylated and label free forms. All Madin-Darby canine kidney (MDCK) cell-propagated viruses with human H3 or classical swine H1 hemagglutinins bound only to Neu5Acalpha2-6Galbeta1-bearing polymers, and not to Neu5Acalpha2-3Galbeta1-bearing polymers. This receptor-binding pattern is typical for human influenza viruses and it differs from the previously described receptor-binding specificity of egg-adapted swine influenza viruses.

Use of real-time reverse transcriptase polymerase chain reaction assay and cell culture methods for detection of swine influenza A viruses.

Objective: To evaluate sensitivity and specificity of a real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay performed on pooled nasal swab specimens, compared with virus isolation performed on individual nasal swab specimens by use of 2 cell culture lines for detection of swine influenza A viruses.

Sample Population: 900 nasal swab specimens obtained from pigs at an abattoir and 62 nasal swab specimens submitted for diagnostic testing.

Procedures: Primers were chosen to amplify a conserved portion of the influenza virus matrix gene.

Characterization of avian H3N3 and H1N1 influenza A viruses isolated from pigs in Canada.

H3N3 and H1N1 influenza A viruses were isolated from Canadian pigs in 2001 and 2002. These viruses are phylogenetically related to waterfowl viruses and antigenically distinct from reference swine influenza viruses. The isolation of these viruses reemphasizes the potential for interspecies transmission of influenza viruses from waterfowl to pigs in North America.

Comparison of the pathogenesis of two genetically different H3N2 influenza A viruses in pigs.

In 1997 and 1998, H3N2 influenza A viruses emerged among pigs in North America. Genetic analyses of the H3N2 isolates demonstrated that they had distinctly different genotypes. The most commonly isolated viruses in the United States have a triple-reassortant genotype, with the hemagglutinin, neuraminidase, and PB1 polymerase genes being of human influenza virus origin, the nucleoprotein, matrix, and nonstructural genes being of classical swine influenza virus origin, and the PA and PB2 polymerase genes being of avian influenza virus origin.

Characterization of a swine-like reassortant H1N2 influenza virus isolated from a wild duck in the United States.

An H1N2 influenza virus (A/Duck/North Carolina/91347/01) (Dk/NC) was isolated from a wild duck in the United States in 2001. Genetic analyses showed that this duck virus has the same human/classical swine/avian reassortant genotype as the H1N2 viruses that have been isolated from pigs and turkeys in the US since 1999. Phylogenetic analyses of each gene segment further confirmed that the Dk/NC virus is closely related to the domestic animal H1N2 isolates.

Genetic characterization of H1N2 influenza A viruses isolated from pigs throughout the United States.

An H1N2 influenza A virus was isolated from a pig in the United States for the first time in 1999 (A. I. Karasin, G.