Novel Swine Influenza Virus Reassortants in Pigs, China

China Agricultural University, Beijing, People's Republic of China.
Emerging Infectious Diseases (Impact Factor: 6.75). 07/2010; 16(7):1162-4. DOI: 10.3201/eid1607.091881
Source: PubMed


During swine influenza virus surveillance in pigs in China during 2006-2009, we isolated subtypes H1N1, H1N2, and H3N2 and found novel reassortment between contemporary swine and avian panzootic viruses. These reassortment events raise concern about generation of novel viruses in pigs, which could have pandemic potential.

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    • "The public health importance of influenza infections in swine arises from the fact that swine are susceptible to co-infections with multiple lineages of the influenza virus, which can generate novel strains via reassortment [8,11]. Reassortant viruses containing genes from pH1N1 and other influenza subtypes have already been isolated from swine in China, the United States, and the United Kingdom [7,12,13]. As a consequence there is concern that the next pandemic strain could arise in swine, although the spread of reassortant virus among humans would require further adaptation in order to replicate efficiently in humans and spread between them [14,15]. "
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    ABSTRACT: The 2009 pH1N1 influenza pandemic resulted in at least 18,500 deaths worldwide. While pH1N1 is now considered to be in a post-pandemic stage in humans it has nevertheless spilled back into swine in at least 20 countries. Understanding the factors that increase the risk of spillover events between swine and humans is essential to predicting and preventing future outbreaks. We assessed risk factors that may have led to spillover of pH1N1 from humans to swine in Cameroon, Central Africa. We sampled swine, domestic poultry and wild birds for influenza A virus at twelve sites in Cameroon from December 2009 while the pandemic was ongoing, to August 2012. At the same time we conducted point-count surveys to assess the abundance of domestic livestock and wild birds and assess interspecific contact rates. Random forest models were used to assess which variables were the best predictors of influenza in swine. We found swine with either active pH1N1 infections or positive for influenza A at four of our twelve sites. Only one swine tested positive by competitive ELISA in 2011-2012. To date we have found pH1N1 only in the North and Extreme North regions of Cameroon (regions in Cameroon are administrative units similar to provinces), though half of our sites are in the Central and Western regions. Swine husbandry practices differ between the North and Extreme North regions where it is common practice in to let swine roam freely, and the Central and Western regions where swine are typically confined to pens. Random forest analyses revealed that the three best predictors of the presence of pH1N1 in swine were contact rates between free-ranging swine and domestic ducks, contact rates between free-ranging swine and wild Columbiformes, and contact rates between humans and ducks. Sites in which swine were allowed to range freely had closer contact with other species than did sites in which swine were kept penned. Results suggest that the practice of allowing swine to roam freely is a significant risk factor for spillover of influenza from humans into swine populations.
    Full-text · Article · Mar 2014 · BMC Veterinary Research
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    • "From our swine influenza surveillance work from 2006 to 2009, samples were inoculated into specific pathogen free (SPF) eggs for viral isolation [8]. It was found that inoculated embryonated eggs of some SIV-positive isolates died during the isolation procedure. "
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    ABSTRACT: Background Influenza virus virulence can be exacerbated by bacterial co-infections. Swine influenza virus (SIV) infection together with some bacteria is found to enhance pathogenicity. Methods SIV-positive samples suspected of containing bacteria were used for bacterial isolation and identification. Antimicrobial susceptibility testing was performed by disc diffusion methods. To investigate the interaction of SIV and the bacteria in vitro, guinea pigs were used as mammalian hosts to determine the effect on viral susceptibility and transmissibility. Differences in viral titers between groups were compared using Student’s t-test. Results During surveillance for SIV in China from 2006 to 2009, seven isolates (24.14%) of 29 influenza A viruses were co-isolated with Stenotrophomonas maltophilia from nasal and tracheal swab samples of pigs. Antimicrobial susceptibility testing showed that the bacteria possessed a high level of resistance towards clinically used antibiotics. To investigate the interaction between these two microorganisms in influencing viral susceptibility and transmission in humans, guinea pigs were used as an infection model. Animals were inoculated with SIV or S. maltophilia alone or co-infected with SIV and S. maltophilia. The results showed that although no transmission among guinea pigs was observed, virus–bacteria co-infections resulted in higher virus titers in nasal washes and trachea and a longer virus shedding period. Conclusions This is the first report of influenza virus co-infection with S. maltophilia in the Chinese swine population. Increased replication of virus by co-infection with multidrug resistant bacteria might increase the infection rate of SIV in humans. The control of S. maltophilia in clinics will contribute to reducing the spread of SIV in pigs and humans.
    Full-text · Article · Aug 2012 · Virology Journal
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    • "Given the fact that swine are susceptible to both human and animal influenza viruses and that pigs have been considered important intermediate hosts, acting as mixing vessels for genetic reassortment (Vincent et al., 2008), the co-circulation of different influenza strains including human and pandemic H1N1 viruses in swine increase the potential of viral reassortment. Thus, novel reassortants may continue to emerge in swine populations around the world (Balint et al., 2009;Bi et al., 2010;Vincent et al., 2009). Here we report the isolation of swine H1N2 reassortant influenza viruses from pigs in OH, U.S. The molecular characterization and phylogenetic analysis of the new isolates revealed that they possess a humanlike HA and NA genes, swine TRIG internal genes PB2, PB1, PA, and NS, and pandemic H1N1 lineage NP and M genes. "
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    ABSTRACT: In October and November 2010, novel H1N2 reassortant influenza viruses were identified from pigs showing mild respiratory signs that included cough and depression. Sequence and phylogenetic analysis showed that the novel H1N2 reassortants possesses HA and NA genes derived from recent H1N2 swine isolates similar to those isolated from Midwest. Compared to the majority of reported reassortants, both viruses preserved human-like host restrictive and putative antigenic sites in their HA and NA genes. The four internal genes, PB2, PB1, PA, and NS were similar to the contemporary swine triple reassortant viruses’ internal genes (TRIG). Interestingly, NP and M genes of the novel reassortants were derived from the 2009 pandemic H1N1. The NP and M proteins of the two isolates demonstrated one (E16G) and four (G34A, D53E, I109T, and V313I) amino acid changes in the M2 and NP proteins, respectively. Similar amino acid changes were also noticed upon incorporation of the 2009 pandemic H1N1 NP in other reassortant viruses reported in the U.S. Thus the role of those amino acids in relation to host adaptation need to be further investigated. The reassortments of pandemic H1N1 with swine influenza viruses and the potential of interspecies transmission of these reassortants from swine to other species including human indicate the importance of systematic surveillance of swine population to determine the origin, the prevalence of similar reassortants in the U.S. and their impact on both swine production and public health.
    Full-text · Article · Feb 2012 · Veterinary Microbiology
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