tetano
Editor, Senior Moderator
Published ahead of print 16 April 2014, doi: 10.1128/JVI.00715-14 JVI.00715-14
Intra-host dynamics of influenza virus reassortment
Hui Tao,
John Steel and
Anice C. Lowen*
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia 30322
ABSTRACT
The segmented nature of the influenza virus genome allows reassortment between co-infecting viruses. This process of genetic exchange vastly increases the diversity of circulating influenza viruses. The importance of reassortment to public health is clear from its role in the emergence of a number of epidemiologically important viruses, including novel pandemic and epidemic strains. To gauge its impact on within-host genomic variation, we tracked reassortment in co-infected guinea pigs over time and given matched or discordant doses of co-infecting viruses. To ensure unbiased detection of reassortants, we used parental viruses of equivalent fitness that differ only by non-coding nucleotide changes. These viruses were based on the isolate A/Panama/2007/1999 (H3N2). At a dose of 2?102 PFU, one parental virus was absent from each guinea pig throughout the time course, indicating the presence of a bottleneck. With an intermediate dose of 2?103 PFU, genomic diversity present in nasal lavage samples increased from 1-3 days post-infection (d.p.i.) and then declined by 6 d.p.i. With a high dose of 2?106 PFU, however, reassortment levels were high (avg. 59%) at 1 d.p.i. and remained stable. Even late in the course of infection, parental viruses were not eclipsed by reassortants, suggesting that a uniformly high multiplicity of infection was not achieved in vivo. Inoculation with approximately 10-fold discordant doses did not reduce reassortment relative to equivalent inputs, but markedly changed the spectrum of genotypes produced. Our data reveal the potential for reassortment to contribute to intra-host diversity in mixed influenza virus infection.
Importance Influenza virus reassortment is prevalent in nature and is a major contributor to the diversity of influenza viruses circulating in avian, swine, human and other host species. This diversity, in turn, increases the potential for influenza viruses to evade selective pressures or adapt to new host environments. As examples, reassortment was key to the emergence of the 1957, 1968 and 2009 pandemics; the unusually severe influenza epidemics of 2003, 1951 and 1947; and the rise in adamantane resistance among currently circulating human H3N2 viruses. Herein we reveal the diversity of viral genotypes generated over time in a host co-infected with two influenza viruses. We find that intra-host diversity driven by reassortment is dynamic and dependent on the amount of each virus initiating infection. Our results demonstrate the readiness with which reassortant influenza viruses arise, offering new insight into this important mechanism of influenza virus evolution.
FOOTNOTES
↵*Address Correspondence: Anice C. Lowen, Department of Microbiology and Immunology, Emory School of Medicine, Rollins Research Center, 1510 Clifton Road, Atlanta, GA 30322, Phone: 404-727-4728, Fax: 404-727-8250, Email: anice.lowen{at}emory.edu
http://jvi.asm.org/content/early/2014/04/10/JVI.00715-14.abstract
Intra-host dynamics of influenza virus reassortment
Hui Tao,
John Steel and
Anice C. Lowen*
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia 30322
ABSTRACT
The segmented nature of the influenza virus genome allows reassortment between co-infecting viruses. This process of genetic exchange vastly increases the diversity of circulating influenza viruses. The importance of reassortment to public health is clear from its role in the emergence of a number of epidemiologically important viruses, including novel pandemic and epidemic strains. To gauge its impact on within-host genomic variation, we tracked reassortment in co-infected guinea pigs over time and given matched or discordant doses of co-infecting viruses. To ensure unbiased detection of reassortants, we used parental viruses of equivalent fitness that differ only by non-coding nucleotide changes. These viruses were based on the isolate A/Panama/2007/1999 (H3N2). At a dose of 2?102 PFU, one parental virus was absent from each guinea pig throughout the time course, indicating the presence of a bottleneck. With an intermediate dose of 2?103 PFU, genomic diversity present in nasal lavage samples increased from 1-3 days post-infection (d.p.i.) and then declined by 6 d.p.i. With a high dose of 2?106 PFU, however, reassortment levels were high (avg. 59%) at 1 d.p.i. and remained stable. Even late in the course of infection, parental viruses were not eclipsed by reassortants, suggesting that a uniformly high multiplicity of infection was not achieved in vivo. Inoculation with approximately 10-fold discordant doses did not reduce reassortment relative to equivalent inputs, but markedly changed the spectrum of genotypes produced. Our data reveal the potential for reassortment to contribute to intra-host diversity in mixed influenza virus infection.
Importance Influenza virus reassortment is prevalent in nature and is a major contributor to the diversity of influenza viruses circulating in avian, swine, human and other host species. This diversity, in turn, increases the potential for influenza viruses to evade selective pressures or adapt to new host environments. As examples, reassortment was key to the emergence of the 1957, 1968 and 2009 pandemics; the unusually severe influenza epidemics of 2003, 1951 and 1947; and the rise in adamantane resistance among currently circulating human H3N2 viruses. Herein we reveal the diversity of viral genotypes generated over time in a host co-infected with two influenza viruses. We find that intra-host diversity driven by reassortment is dynamic and dependent on the amount of each virus initiating infection. Our results demonstrate the readiness with which reassortant influenza viruses arise, offering new insight into this important mechanism of influenza virus evolution.
FOOTNOTES
↵*Address Correspondence: Anice C. Lowen, Department of Microbiology and Immunology, Emory School of Medicine, Rollins Research Center, 1510 Clifton Road, Atlanta, GA 30322, Phone: 404-727-4728, Fax: 404-727-8250, Email: anice.lowen{at}emory.edu
http://jvi.asm.org/content/early/2014/04/10/JVI.00715-14.abstract