In vivo evaluation of vaccine efficacy against challenge with a contemporary field isolate from the α cluster of H1N1 swine influenza virus.

Influenza A virus vaccines currently contain a mixture of isolates that reflect the genetic and antigenic characteristics of the currently circulating strains. This study was conducted to evaluate the efficacy of a trivalent inactivated swine influenza virus vaccine (Flusure XP) in pigs challenged with a contemporary α-cluster H1N1 field isolate of Canadian swine origin. Pigs were allocated to vaccinated, placebo, and negative-control groups and monitored for respiratory disease for 5 d after challenge.

The impact of maternally derived immunity on influenza A virus transmission in neonatal pig populations.

The commonality of influenza A virus (IAV) exposure and vaccination on swine farms in the United States ensures that the majority of neonatal pigs will have some degree of maternal immunity to IAV. The influence of maternal immunity on IAV transmission in neonatal pig populations will impact virus prevalence and infection dynamics across pig populations. The main objective of this study was to assess the impact of maternally derived immunity on IAV transmission in an experimental setting.

Relationship between airborne detection of influenza A virus and the number of infected pigs.

Influenza A virus infects a wide range of species including both birds and mammals (including humans). One of the key routes by which the virus can infect populations of animals is by aerosol transmission. This study explored the relationship between number of infected pigs and the probability of detecting influenza virus RNA in bioaerosols through the course of an acute infection.

Neutralizing DNA aptamers against swine influenza H3N2 viruses.

Triple reassortant influenza A viruses (IAVs) of swine, particularly the North American H3N2 subtype, circulate in swine herds and may reassort and result in the emergence of novel zoonotic strains. Current diagnostic tools rely on isolation of the viruses, followed by serotyping by hemagglutination or genome sequencing, both of which can be expensive and time-consuming. Thus, novel subtype-specific ligands and methods are needed for rapid testing and subtyping of IAVs in the field.

Comparison of Human-Like H1 (δ-Cluster) Influenza A Viruses in the Swine Host.

Influenza A viruses cause acute respiratory disease in swine. Viruses with H1 hemagglutinin genes from the human seasonal lineage (δ-cluster) have been isolated from North American swine since 2003. The objective of this work was to study the pathogenesis and transmission of δ-cluster H1 influenza viruses in swine, comparing three isolates from different phylogenetic subclusters, geographic locations, and years of isolation.

Genomic reassortment of influenza A virus in North American swine, 1998-2011.

Revealing the frequency and determinants of reassortment among RNA genome segments is fundamental to understanding basic aspects of the biology and evolution of the influenza virus. To estimate the extent of genomic reassortment in influenza viruses circulating in North American swine, we performed a phylogenetic analysis of 139 whole-genome viral sequences sampled during 1998-2011 and representing seven antigenically distinct viral lineages. The highest amounts of reassortment were detected between the H3 and the internal gene segments (PB2, PB1, PA, NP, M and NS), while the lowest reassortment frequencies were observed among the H1γ, H1pdm and neuraminidase segments, particularly N1.

Global transmission of influenza viruses from humans to swine.

To determine the extent to which influenza viruses jump between human and swine hosts, we undertook a large-scale phylogenetic analysis of pandemic A/H1N1/09 (H1N1pdm09) influenza virus genome sequence data. From this, we identified at least 49 human-to-swine transmission events that occurred globally during 2009-2011, thereby highlighting the ability of the H1N1pdm09 virus to transmit repeatedly from humans to swine, even following adaptive evolution in humans. Similarly, we identified at least 23 separate introductions of human seasonal (non-pandemic) H1 and H3 influenza viruses into swine globally since 1990.

Evolution of novel reassortant A/H3N2 influenza viruses in North American swine and humans, 2009-2011.

Novel H3N2 influenza viruses (H3N2v) containing seven genome segments from swine lineage triple-reassortant H3N2 viruses and a 2009 pandemic H1N1 (H1N1pdm09) matrix protein segment (pM) were isolated from 12 humans in the United States between August and December 2011. To understand the evolution of these novel H3N2 viruses in swine and humans, we undertook a phylogenetic analysis of 674 M sequences and 388 HA and NA sequences from influenza viruses isolated from North American swine during 2009-2011, as well as HA, NA, and M sequences from eight H3N2v viruses isolated from humans. We identified 34 swine influenza viruses (termed rH3N2p) with the same combination of H3, N2, and pM segments as the H3N2v viruses isolated from humans.

Pathogenicity and transmission in pigs of the novel A(H3N2)v influenza virus isolated from humans and characterization of swine H3N2 viruses isolated in 2010-2011.

Swine influenza virus (SIV) H3N2 with triple reassorted internal genes (TRIG) has been enzootic in Unites States since 1998. Transmission of the 2009 pandemic H1N1 (pH1N1) virus to pigs in the United States was followed by reassortment with endemic SIV, resulting in reassorted viruses that include novel H3N2 genotypes (rH3N2p). Between July and December 2011, 12 cases of human infections with swine-lineage H3N2 viruses containing the pandemic matrix (pM) gene [A(H3N2)v] were detected.

Genetic composition of contemporary swine influenza viruses in the West Central region of the United States of America.

Background: Because of continuous circulation in different animal species and humans, influenza viruses have host-specific phenotypic and genetic features. Reassortment of the genome segments can significantly change virus phenotype, potentially generating virus with pandemic potential. In 2009, a new pandemic influenza virus emerged.

Detection of Influenza A virus in porcine oral fluid samples.

Porcine oral fluids have been used for the detection of Porcine reproductive and respiratory syndrome virus and Porcine circovirus-2. The objective of the present study was to determine whether Influenza A virus (FLUAV) is present in porcine oral fluids at detectable levels and to validate a standard FLUAV molecular diagnostic test for porcine oral fluids. Pen-based oral fluid samples were collected on 3, 4, 5, and 6 days postinfection (DPI) from 4 groups of 6 pigs each that were inoculated intratracheally with A/Swine/Iowa/00239/2004 H1N1 and from 2 untreated or mock-inoculated groups of 6 pigs each that served as negative controls.

Comparison of the receptor binding properties of contemporary swine isolates and early human pandemic H1N1 isolates (Novel 2009 H1N1).

We have utilized glycan microarray technology to determine the receptor binding properties of early isolates from the recent 2009 H1N1 human pandemic (pdmH1N1), and compared them to North American swine influenza isolates from the same year, as well as past seasonal H1N1 human isolates. We showed that the pdmH1N1 strains, as well as the swine influenza isolates examined, bound almost exclusively to glycans with α2,6-linked sialic acid with little binding detected for α2,3-linked species. This is highlighted by pair-wise comparisons between compounds with identical glycan backbones, differing only in the chemistry of their terminal linkages.

Genetic and antigenic characterization of H1 influenza viruses from United States swine from 2008.

Prior to the introduction of the 2009 pandemic H1N1 virus from humans into pigs, four phylogenetic clusters (α-, β-, γ- and δ) of the haemagglutinin (HA) gene from H1 influenza viruses could be found in US swine. Information regarding the antigenic relatedness of the H1 viruses was lacking due to the dynamic and variable nature of swine lineage H1. We characterized 12 H1 isolates from 2008 by using 454 genome-sequencing technology and phylogenetic analysis of all eight gene segments and by serological cross-reactivity in the haemagglutination inhibition (HI) assay.

Antiviral susceptibility of avian and swine influenza virus of the N1 neuraminidase subtype.

Influenza viruses of the N1 neuraminidase (NA) subtype affecting both animals and humans caused the 2009 pandemic. Anti-influenza virus NA inhibitors are crucial early in a pandemic, when specific influenza vaccines are unavailable. Thus, it is urgent to confirm the antiviral susceptibility of the avian viruses, a potential source of a pandemic virus.

Swine influenza matrix 2 (M2) protein contributes to protection against infection with different H1 swine influenza virus (SIV) isolates.

A swine influenza virus (SIV) vaccine-challenge pig model was used to study the potential of a conserved matrix 2 (M2) protein vaccine alone or in combination with an inactivated H1N1-vaccine to protect against H1N1 and H1N2 viruses. The H1N1-vaccine and heterologous H1N2-challenge virus model has previously been shown to prolong fever and increase SIV-associated pneumonic lesions. The M2 vaccine in combination with the H1N1-vaccine reduced the H1N2 induced fever but not virus shedding.

The feasibility of using high resolution genome sequencing of influenza A viruses to detect mixed infections and quasispecies.

Background: The rapidly expanding availability of de novo sequencing technologies can greatly facilitate efforts to monitor the relatively high mutation rates of influenza A viruses and the detection of quasispecies. Both the mutation rates and the lineages of influenza A viruses are likely to play an important role in the natural history of these viruses and the emergence of phenotypically and antigenically distinct strains.

Methodology And Principal Findings: We evaluated quasispecies and mixed infections by de novo sequencing the whole genomes of 10 virus isolates, including eight avian influenza viruses grown in embryonated chicken eggs (six waterfowl isolates - five H3N2 and one H4N6; an H7N3 turkey isolate; and a bald eagle isolate with H1N1/H2N1 mixed infection), and two tissue cultured H3N2 swine influenza viruses.

Characterization of a newly emerged genetic cluster of H1N1 and H1N2 swine influenza virus in the United States.

H1 influenza A viruses that were distinct from the classical swine H1 lineage were identified in pigs in Canada in 2003–2004; antigenic and genetic characterization identified the hemagglutinin (HA) as human H1 lineage. The viruses identified in Canadian pigs were human lineage in entirety or double (human–swine) reassortants. Here, we report the whole genome sequence analysis of four human-like H1 viruses isolated from U.

Identification of H2N3 influenza A viruses from swine in the United States.

Although viruses of each of the 16 influenza A HA subtypes are potential human pathogens, only viruses of the H1, H2, and H3 subtype are known to have been successfully established in humans. H2 influenza viruses have been absent from human circulation since 1968, and as such they pose a substantial human pandemic risk. In this report, we isolate and characterize genetically similar avian/swine virus reassortant H2N3 influenza A viruses isolated from diseased swine from two farms in the United States.

Failure of protection and enhanced pneumonia with a US H1N2 swine influenza virus in pigs vaccinated with an inactivated classical swine H1N1 vaccine.

Two US swine influenza virus (SIV) isolates, A/Swine/Iowa/15/1930 H1N1 (IA30) and A/Swine/Minnesota/00194/2003 H1N2 (MN03), were evaluated in an in vivo vaccination and challenge model. Inactivated vaccines were prepared from each isolate and used to immunize conventional pigs, followed by challenge with homologous or heterologous virus. Both inactivated vaccines provided complete protection against homologous challenge.

Efficacy of swine influenza A virus vaccines against an H3N2 virus variant.

We compared the efficacy of 3 commercial vaccines against swine influenza A virus (SIV) and an experimental homologous vaccine in young pigs that were subsequently challenged with a variant H3N2 SIV, A/Swine/Colorado/00294/2004, selected from a repository of serologically and genetically characterized H3N2 SIV isolates obtained from recent cases of swine respiratory disease. The experimental vaccine was prepared from the challenge virus. Four groups of 8 pigs each were vaccinated intramuscularly at both 4 and 6 wk of age with commercial or homologous vaccine.

Serologic and genetic characterization of North American H3N2 swine influenza A viruses.

The H3N2 subtype of influenza A viruses isolated from pigs in the United States and Canada has shown both genetic and antigenic diversity. The objective of this study was to determine the serologic and genetic characteristics of contemporary strains of these viruses. Genetic analysis of 18 reference strains and 8 selected strains demonstrated differences in 1% to 9% of the nucleotides of the hemagglutinin (HA) gene.

Evaluation of hemagglutinin subtype 1 swine influenza viruses from the United States.

Swine influenza viruses (SIV) of the hemagglutinin subtype 1 (H1) isolated from the United States (U.S.) have not been well-characterized in the natural host.