Emergence of Highly Pathogenic Avian Influenza A(H5N1) Virus PB1-F2 Variants and Their Virulence in BALB/c Mice

ABSTRACTInfluenza A viruses (IAVs) express the PB1-F2 protein from an alternate reading frame within the PB1 gene segment. The roles of PB1-F2 are not well understood but appear to involve modulation of host cell responses. As shown in previous studies, we find that PB1-F2 proteins of mammalian IAVs frequently have premature stop codons that are expected to cause truncations of the protein, whereas avian IAVs usually express a full-length 90-amino-acid PB1-F2. However, in contrast to other avian IAVs, recent isolates of highly pathogenic H5N1 influenza viruses had a high proportion of PB1-F2 truncations (15% since 2010; 61% of isolates in 2013) due to several independent mutations that have persisted and expanded in circulating viruses. One natural H5N1 IAV containing a mutated PB1-F2 start codon (i.e., lacking ATG) was 1,000-fold more virulent for BALB/c mice than a closely related H5N1 containing intact PB1-F2.In vitro, we detected expression of an in-frame protein (C-terminal PB1-F2) from downstream ATGs in PB1-F2 plasmids lacking the well-conserved ATG start codon. Transient expression of full-length PB1-F2, truncated (24-amino-acid) PB1-F2, and PB1-F2 lacking the initiating ATG in mammalian and avian cells had no effect on cell apoptosis or interferon expression in human lung epithelial cells. Full-length and C-terminal PB1-F2 mutants colocalized with mitochondria in A549 cells. Close monitoring of alterations of PB1-F2 and their frequency in contemporary avian H5N1 viruses should continue, as such changes may be markers for mammalian virulence.IMPORTANCEAlthough most avian influenza viruses are harmless for humans, some (such as highly pathogenic H5N1 avian influenza viruses) are capable of infecting humans and causing severe disease with a high mortality rate. A number of risk factors potentially associated with adaptation to mammalian infection have been noted. Here we demonstrate that the protein PB1-F2 is frequently truncated in recent isolates of highly pathogenic H5N1 viruses. Truncation of PB1-F2 has been proposed to act as an adaptation to mammalian infection. We show that some forms of truncation of PB1-F2 may be associated with increased virulence in mammals. Our data support the assessment of PB1-F2 truncations for genomic surveillance of influenza viruses.

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Antibody responses to avian influenza viruses in wild birds broaden with age

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2016.2159 ◽

2016 ◽

Vol 283 (1845) ◽

pp. 20162159 ◽

Cited By ~ 11

Author(s):

Sarah C. Hill ◽

Ruth J. Manvell ◽

Bodo Schulenburg ◽

Wendy Shell ◽

Paul S. Wikramaratna ◽

...

Keyword(s):

Avian Influenza ◽

Haemagglutination Inhibition ◽

Wild Birds ◽

Influenza Viruses ◽

Antibody Responses ◽

Immune Recognition ◽

Avian Influenza Viruses ◽

Highly Pathogenic ◽

Age Related ◽

Pathogenic H5n1

For viruses such as avian influenza, immunity within a host population can drive the emergence of new strains by selecting for viruses with novel antigens that avoid immune recognition. The accumulation of acquired immunity with age is hypothesized to affect how influenza viruses emerge and spread in species of different lifespans. Despite its importance for understanding the behaviour of avian influenza viruses, little is known about age-related accumulation of immunity in the virus's primary reservoir, wild birds. To address this, we studied the age structure of immune responses to avian influenza virus in a wild swan population ( Cygnus olor ), before and after the population experienced an outbreak of highly pathogenic H5N1 avian influenza in 2008. We performed haemagglutination inhibition assays on sampled sera for five avian influenza strains and show that breadth of response accumulates with age. The observed age-related distribution of antibody responses to avian influenza strains may explain the age-dependent mortality observed during the highly pathogenic H5N1 outbreak. Age structures and species lifespan are probably important determinants of viral epidemiology and virulence in birds.

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A clue to the molecular mechanism of virulence of highly pathogenic H5N1 avian influenza viruses isolated in 2004

Uirusu ◽

10.2222/jsv.55.55 ◽

2005 ◽

Vol 55 (1) ◽

pp. 55-61 ◽

Cited By ~ 3

Author(s):

Masato HATTA ◽

Yoshihiro KAWAOKA

Keyword(s):

Avian Influenza ◽

Molecular Mechanism ◽

Influenza Viruses ◽

Avian Influenza Viruses ◽

Highly Pathogenic ◽

H5n1 Avian Influenza ◽

Pathogenic H5n1

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Highly Pathogenic H5N1 Avian Influenza Viruses Exhibit Few Barriers to Gene Flow in Vietnam

EcoHealth ◽

10.1007/s10393-012-0749-7 ◽

2012 ◽

Vol 9 (1) ◽

pp. 60-69 ◽

Cited By ~ 3

Author(s):

Margaret Carrel ◽

Xiu-Feng Wan ◽

Tung Nguyen ◽

Michael Emch

Keyword(s):

Gene Flow ◽

Avian Influenza ◽

Influenza Viruses ◽

Avian Influenza Viruses ◽

Highly Pathogenic ◽

H5n1 Avian Influenza ◽

Pathogenic H5n1

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Genetic Variation of Highly Pathogenic H5N1 Avian Influenza Viruses in Vietnam Shows Both Species-Specific and Spatiotemporal Associations

Avian Diseases Digest ◽

10.1637/9926-978511-digest.1 ◽

2011 ◽

Vol 6 (4) ◽

pp. e25-e27

Author(s):

Margaret Carrel ◽

Xiu-Feng Wan ◽

Tung Nguyen ◽

Michael Emch

Keyword(s):

Genetic Variation ◽

Avian Influenza ◽

Influenza Viruses ◽

Avian Influenza Viruses ◽

Highly Pathogenic ◽

H5n1 Avian Influenza ◽

Species Specific ◽

Pathogenic H5n1

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Molecular characterization of the surface glycoprotein genes of highly pathogenic H5N1 avian influenza viruses detected in Iran in 2011

Tropical Animal Health and Production ◽

10.1007/s11250-013-0528-7 ◽

2014 ◽

Vol 46 (3) ◽

pp. 549-554 ◽

Cited By ~ 4

Author(s):

Ebrahim Kord ◽

Amir Kaffashi ◽

Hadi Ghadakchi ◽

Fatemeh Eshratabadi ◽

Zakaria Bameri ◽

...

Keyword(s):

Avian Influenza ◽

Molecular Characterization ◽

Influenza Viruses ◽

Surface Glycoprotein ◽

Avian Influenza Viruses ◽

Highly Pathogenic ◽

H5n1 Avian Influenza ◽

Pathogenic H5n1

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Pathogenesis and Transmission Assessments of Two H7N8 Influenza A Viruses Recently Isolated from Turkey Farms in Indiana Using Mouse and Ferret Models

Journal of Virology ◽

10.1128/jvi.01646-16 ◽

2016 ◽

Vol 90 (23) ◽

pp. 10936-10944 ◽

Cited By ~ 13

Author(s):

Xiangjie Sun ◽

Jessica A. Belser ◽

Joanna A. Pulit-Penaloza ◽

Hui Zeng ◽

Amanda Lewis ◽

...

Keyword(s):

Avian Influenza ◽

Influenza A ◽

Influenza Viruses ◽

Avian Influenza Viruses ◽

Highly Pathogenic ◽

Pathogenic Avian Influenza ◽

Domestic Poultry ◽

Commercial Turkey

ABSTRACTAvian influenza A H7 viruses have caused multiple outbreaks in domestic poultry throughout North America, resulting in occasional infections of humans in close contact with affected birds. In early 2016, the presence of H7N8 highly pathogenic avian influenza (HPAI) viruses and closely related H7N8 low-pathogenic avian influenza (LPAI) viruses was confirmed in commercial turkey farms in Indiana. These H7N8 viruses represent the first isolation of this subtype in domestic poultry in North America, and their virulence in mammalian hosts and the potential risk for human infection are largely unknown. In this study, we assessed the ability of H7N8 HPAI and LPAI viruses to replicatein vitroin human airway cells andin vivoin mouse and ferret models. Both H7N8 viruses replicated efficientlyin vitroandin vivo, but they exhibited substantial differences in disease severity in mammals. In mice, while the H7N8 LPAI virus largely remained avirulent, the H7N8 HPAI virus exhibited greater infectivity, virulence, and lethality. Both H7N8 viruses replicated similarly in ferrets, but only the H7N8 HPAI virus caused moderate weight loss, lethargy, and mortality. The H7N8 LPAI virus displayed limited transmissibility in ferrets placed in direct contact with an inoculated animal, while no transmission of H7N8 HPAI virus was detected. Our results indicate that the H7N8 avian influenza viruses from Indiana are able to replicate in mammals and cause severe disease but with limited transmission. The recent appearance of H7N8 viruses in domestic poultry highlights the need for continued influenza surveillance in wild birds and close monitoring of the potential risk to human health.IMPORTANCEH7 influenza viruses circulate in wild birds in the United States, but when the virus emerges in domestic poultry populations, the frequency of human exposure and the potential for human infections increases. An H7N8 highly pathogenic avian influenza (HPAI) virus and an H7N8 low-pathogenic avian influenza (LPAI) virus were recently isolated from commercial turkey farms in Indiana. To determine the risk that these influenza viruses pose to humans, we assessed their pathogenesis and transmissionin vitroand in mammalian models. We found that the H7N8 HPAI virus exhibited enhanced virulence, and although transmission was only observed with the H7N8 LPAI virus, the ability of this H7 virus to transmit in a mammalian host and quickly evolve to a more virulent strain is cause for concern. Our findings offer important insight into the potential for emerging H7 avian influenza viruses to acquire the ability to cause disease and transmit among mammals.

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