Lack of transmission of H5N1 avian–human reassortant influenza viruses in a ferret model

Abstract

Avian influenza A H5N1 viruses continue to spread globally among birds, resulting in occasional transmission of virus from infected poultry to humans. Probable human-to-human transmission has been documented rarely, but H5N1 viruses have not yet acquired the ability to transmit efficiently among humans, an essential property of a pandemic virus. The pandemics of 1957 and 1968 were caused by avian-human reassortant influenza viruses that had acquired human virus-like receptor binding properties. However, the relative contribution of human internal protein genes or other molecular changes to the efficient transmission of influenza viruses among humans remains poorly understood. Here, we report on a comparative ferret model that parallels the efficient transmission of H3N2 human viruses and the poor transmission of H5N1 avian viruses in humans. In this model, an H3N2 reassortant virus with avian virus internal protein genes exhibited efficient replication but inefficient transmission, whereas H5N1 reassortant viruses with four or six human virus internal protein genes exhibited reduced replication and no transmission. These findings indicate that the human virus H3N2 surface protein genes alone did not confer efficient transmissibility and that acquisition of human virus internal protein genes alone was insufficient for this 1997 H5N1 virus to develop pandemic capabilities, even after serial passages in a mammalian host. These results highlight the complexity of the genetic basis of influenza virus transmissibility and suggest that H5N1 viruses may require further adaptation to acquire this essential pandemic trait. transmissibility ͉ pandemic virus properties ͉ pandemic influenza ͉ animal model ͉ receptor specificity

Influenza virus aerosol exposure and analytical system for ferrets

“…Aerosol inoculation of mice and guinea pigs has been reported, but aerosol system validation and dosimetry were not described (23,24). Previous ferret studies in which high-dose IN inoculations (≥10,000 FID 50 ) of PN99 and TH16 viruses were administered for pathotype and transmissibility assessment report peak nasal wash titers similar to those achieved by any of the AR inoculations performed here (8,10,14). However, a difference in kinetics was observed; high-dose IN inoculations resulted in earlier peak titers (1 dpi) compared with lower dose IN or AR inoculations.…”

“…The ferret has become widely recognized as an excellent model of influenza virus transmission and pathogenesis, primarily because this host is naturally susceptible to influenza virus infection, displays clinical signs similar to those of infected humans, and reflects the general transmissibility phenotypes of influenza viruses reported in humans (6,(8)(9)(10)(11)(12)(13). Typically, inoculation of animal models is achieved by intranasal (IN) administration of a liquid virus suspension.…”

“…The relative predominance of these different modes of influenza virus transmission in different settings remains controversial and is a major public health question that needs to be addressed. Mammalian models of influenza transmission have been developed to better understand the process of transmission and to rapidly identify the emerging influenza viruses with transmissibility properties that may confer pandemic potential (5-8).The ferret has become widely recognized as an excellent model of influenza virus transmission and pathogenesis, primarily because this host is naturally susceptible to influenza virus infection, displays clinical signs similar to those of infected humans, and reflects the general transmissibility phenotypes of influenza viruses reported in humans (6,(8)(9)(10)(11)(12)(13). Typically, inoculation of animal models is achieved by intranasal (IN) administration of a liquid virus suspension.…”

“…The relative predominance of these different modes of influenza virus transmission in different settings remains controversial and is a major public health question that needs to be addressed. Mammalian models of influenza transmission have been developed to better understand the process of transmission and to rapidly identify the emerging influenza viruses with transmissibility properties that may confer pandemic potential (5)(6)(7)(8).…”

Antigenic drift in the evolution of H1N1 influenza A viruses resulting from deletion of a single amino acid in the haemagglutinin gene

“…Based on the phylogenetic tree, three strains were chosen for reverse genetic experiments to examine the genetic basis of the antigenic differences that arose during this period; A/ Hebei/52/94 was the Chinese virus precursor to the deletion mutant, A/Beijing/262/95, and A/Shenzhen/227/ 95 from the A/Bayern/7/95-like lineage, which did not give rise to a deletion and eventually became extinct. Viral RNA (vRNA) was extracted from A/Hebei/52/94-, A/ Beijing/262/95-and A/Shenzhen/227/95-infected chicken allantoic fluid using the QIAamp vRNA kit (Qiagen) and the full-length HA and NA genes were amplified and cloned into the bidirectional vector pBD as described previously (Maines et al, 2006). Lysine was inserted at position 134 in the A/Beijing/262/95 HA gene, or deleted in the A/Hebei/52/94 and A/Shenzhen/227/95 HA genes using the QuikChange Site-Directed Mutagenesis kit (Stratagene), and the resulting wild-type and mutant plasmids were sequenced both to confirm the plasmid identities and the absence of additional changes.…”