Genetic Compatibility and Virulence of Reassortants Derived from Contemporary Avian H5N1 and Human H3N2 Influenza A Viruses

Abstract

The segmented structure of the influenza virus genome plays a pivotal role in its adaptation to new hosts and the emergence of pandemics. Despite concerns about the pandemic threat posed by highly pathogenic avian influenza H5N1 viruses, little is known about the biological properties of H5N1 viruses that may emerge following reassortment with contemporary human influenza viruses. In this study, we used reverse genetics to generate the 63 possible virus reassortants derived from H5N1 and H3N2 viruses, containing the H5N1 surface protein genes, and analyzed their viability, replication efficiency, and mouse virulence. Specific constellations of avian–human viral genes proved deleterious for viral replication in cell culture, possibly due to disruption of molecular interaction networks. In particular, striking phenotypes were noted with heterologous polymerase subunits, as well as NP and M, or NS. However, nearly one-half of the reassortants replicated with high efficiency in vitro, revealing a high degree of compatibility between avian and human virus genes. Thirteen reassortants displayed virulent phenotypes in mice and may pose the greatest threat for mammalian hosts. Interestingly, one of the most pathogenic reassortants contained avian PB1, resembling the 1957 and 1968 pandemic viruses. Our results reveal the broad spectrum of phenotypes associated with H5N1/H3N2 reassortment and a possible role for the avian PB1 in the emergence of pandemic influenza. These observations have important implications for risk assessment of H5N1 reassortant viruses detected in surveillance programs.

Reassortment between avian H5N1 and human H3N2 influenza viruses creates hybrid viruses with substantial virulence

“…Strikingly, three viruses exhibited substantial lethality for mice with MLD 50 s of ≤10 pfu. Our data suggest that of the eight segments in the human virus, Tok07 PB2 is indispensible for the conversion of reassortant H5 viruses into the highly pathogenic phenotype and that, in contrast to the findings of Chen et al (9), viruses with substantial virulence indeed can be generated by reassortment of avian H5N1 and human H3N2 viruses. Our study thus provides valuable information for preparedness for future pandemics that could be caused by reassortants between avian H5N1 and human influenza viruses, including the recently emerged pandemic H1N1 virus.…”

“…It therefore is important to evaluate the pathogenicity of such reassortants. Chen et al (9) attempted to generate 63 (2 6 − 1 parent virus) reassortant viruses between A/Thailand/16/04 (H5N1) and A/Wyoming/3/03 (H3N2) viruses containing the H5N1 HA and NA genes, together with an additional virus that had H5 HA and N2 NA genes and tested the virulence in mice of 39 of the reassortant viruses generated. They found that these reassortant viruses displayed a broad spectrum of pathogenicity in the mouse model.…”

“…We therefore asked whether the findings of Chen et al (9) could be generalized to all the avian H5N1 and human H3N2 influenza viruses currently cocirculating. To answer this question, we systematically generated all 254 (2 8 − 2 parent viruses) combinations of reassortant viruses between the avian H5N1 (A/Chicken/South Kalimantan/UT6028/06, SK06) and human H3N2 (A/Tokyo/Ut-Sk-1/07, Tok07) influenza viruses and tested the pathogenicity in mice of 75 reassortant viruses with H5 HA genes, which potentially would pose the greatest threat to humans.…”

Adaptive strategies of the influenza virus polymerase for replication in humans

“…The wholesale acquisition of polymerase genes encoding PB1 has been observed in two prior pandemic outbreaks; viruses responsible for the ''Asian'' influenza pandemic in 1957 and the ''Hong Kong'' influenza pandemic in 1968 were reassortants that contained a PB1 subunit of avian origin with the remainder of the polymerase derived from a human virus (29). Experimental analysis has shown that in certain cases, reassorted human influenza polymerases containing an avian PB1 have enhanced activity (30) or support a more pathogenic infection (31), although the potential contribution of PB1-F2 cannot be excluded (32). The current 2009 A(H1N1) pandemic virus is a reassortant as well, containing a replication complex composed of avian-origin PB2 and PA, human-origin PB1, and classic swine-origin NP (21,28).…”

Differential proteomic analysis of respiratory samples from patients suffering from influenza

“…In the last years great efforts have been undertaken to reveal the mechanisms of influenza-host cell interactions. Studies focused either on pathogenesis in humans [11], discovery of novel drug targets, antiviral therapies and biomarker research [1], or on analysis of virulence and adaptation strategies of avian influenza virus [5]. Among the Influenza viruses, influenza A has been shown to interact with host cell proteins throughout the virus life cycle [34].…”