Phone dating 619 954 4608
This virus retained the N2 NA from the circulating H2N2 viruses, but acquired an H3 HA, as well as a PB1 segment, of avian origin ( First reported in China in the spring of 1977, an H1N1 virus began to cause disease in young adults under the age of 23 years.
The high level of similarity between this virus and those circulating in the early 1950s prior to the H2N2 outbreak () prompts the suspicion that the 1977 H1N1 virus was an accidental release from a laboratory stock.
By June 11, 2009, the causative agent, 2009 S-OIV, had spread to 74 countries and been confirmed in nearly 29,000 patients, prompting the World Health Organization to raise the global pandemic alert level to 6, the pandemic phase ().
Genetic analysis suggests that 2009 S-OIV is composed of segments from two H1N1 swine virus lineages: classical swine viruses, which are descendents of the 1918 human influenza virus, and European avian-like influenza viruses (Figure 2 and refs. In the late 1990s, reassortment among North American avian, human H3N2, and classical swine H1N1 viruses resulted in triple-reassortant H3N2 and H1N2 swine viruses.
This observation agrees with the hypothesis that 2009 S-OIV had been circulating within the swine population asymptomatically prior to its transmission to humans, although definitive evidence will require the isolation of recent ancestors of 2009 S-OIV ().
To initiate infection, influenza virus HA binds to sialic acid–containing receptors on the target cell surface, triggering receptor-mediated endocytosis and subsequent fusion within the low-p H environment of the endosome ().These data suggest that HAs in swine viruses can remain antigenically frozen in time because of the lack of selection pressure in this host and can reemerge in the future.The 2009 S-OIV virus contains none of the hallmarks of highly pathogenic influenza viruses (see below), although results from infection of animal models suggest that this virus produces a more severe disease than seasonal H1N1 viruses ().However, pathogen-free animal models may be more reflective of the disease observed in the immunologically naive, younger human population, which was more susceptible to severe disease.Moreover, all seasonal, contemporary H1N1 strains are not created equally.
The nonstructural (NS) gene encodes two proteins: NS1 functions in evading host immune responses by limiting cellular IFN production and the activity of IFN-stimulated genes (ISGs); NEP mediates the export of viral RNPs (v RNPs) from the nucleus.