Since 1997, highly pathogenic avian influenza viruses of the H5N1 subtype have infected humans with high case fatality rates, although no sustained human-to-human transmission has yet been reported. Currently, the molecular features and mechanisms that would result in human-to-human transmission of H5N1 viruses are not fully understood. Indeed, several attempts in the past to select transmissible H5 viruses (which typically do not transmit among mammals) were not successful, suggesting that influenza virus transmissibility is determined by several currently unknown factors. Recently, we screened H5 virus libraries possessing random mutations in the globular head region of the hemagglutinin (HA) protein and identified mutant H5 HAs that acquired the ability to bind to human-type receptors. These mutant H5 HAs did not support virus transmission among ferrets (an established influenza virus transmission model) via respiratory droplets, but acquired this ability after two passages of the virus in these animals, which resulted in the selection of additional mutations in HA. This marks the first conversion of an H5 virus that does not transmit among ferrets into one with efficient respiratory droplet transmission. Based on this finding, we propose to decipher the determinants of H5N1 virus transmission in mammals.
In Aim 1, we plan """"""""To Identify the Mechanisms That Control H5N1 Virus Transmissibility in Mammals"""""""". To gain a better understanding of the mutations in HA that result in transmissible viruses, we will select transmissible viruses based on H5 HA proteins derived from different subclades that have caused human infections. Our recent study suggested that HA stability may contribute to virus transmissibility. To test this concept, we also plan to identify mutations in HA that increase HA stability and then test these mutations for their significance in virus transmissibility. The HA proteins of all ferret-transmissible H5N1 viruses will then be characterized for their receptor-binding specificity, their structural consequences, their effects in other genetic backgrounds, and their pathogenicity in mice and ferrets. Mutations in HA that allow avian influenza viruses to bind to human-type receptors are most likely a prerequisite for transmission among mammals;however, findings by us and others indicate that human-type receptor binding is not sufficient for respiratory droplet transmission among ferrets, and that other viral genes also contribute to transmissibility.
In Aim 2 (""""""""To Characterize the Contribution of Viral Genes Other than HA to H5N1 Virus Transmissibility"""""""", we plan to passage non-transmissible viruses of different genetic backgrounds in ferrets to select transmissible mutants. Selected mutations will be characterized for their biological effects, using established assays for internalization, intracellular transport replication and transcription, assembly and budding, and interferon antagonism. Collectively, these studies are expected to generate critical information about the molecular determinants and mechanisms of H5N1 virus transmissibility in mammals.

Public Health Relevance

Our research seeks to understand the mechanisms that would allow highly pathogenic avian H5N1 influenza viruses to infect humans and transmit among them. This information is critical for basic research and the public health sector to monitor circulating and newly emerging H5N1 strains for their pandemic potential and to develop countermeasures to such viruses.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
3R01AI069274-07S1
Application #
8897039
Study Section
Virology - B Study Section (VIRB)
Program Officer
Hauguel, Teresa M
Project Start
2006-05-01
Project End
2017-08-31
Budget Start
2014-09-01
Budget End
2015-08-31
Support Year
7
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of Wisconsin Madison
Department
Pathology
Type
Schools of Veterinary Medicine
DUNS #
City
Madison
State
WI
Country
United States
Zip Code
53715
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Moncla, Louise H; Zhong, Gongxun; Nelson, Chase W et al. (2016) Selective Bottlenecks Shape Evolutionary Pathways Taken during Mammalian Adaptation of a 1918-like Avian Influenza Virus. Cell Host Microbe 19:169-80
Neumann, Gabriele (2015) H5N1 influenza virulence, pathogenicity and transmissibility: what do we know? Future Virol 10:971-980
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Imai, Masaki; Watanabe, Tokiko; Hatta, Masato et al. (2012) Experimental adaptation of an influenza H5 HA confers respiratory droplet transmission to a reassortant H5 HA/H1N1 virus in ferrets. Nature 486:420-8
Russell, Colin A; Fonville, Judith M; Brown, André E X et al. (2012) The potential for respiratory droplet-transmissible A/H5N1 influenza virus to evolve in a mammalian host. Science 336:1541-7

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