Viral adaptation to host species: assessing sequence variability in the genome of host adapted avian influenza viruses of a common origin
Date
2015
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Publisher
University of Delaware
Abstract
Migratory waterfowl and shorebirds routinely carry LPAIVs within their intestinal tract year round. Infection with more than one strain of AIV is possible and common. As a result of direct or indirect contact with AIV infected waterfowl, other avian species can contract the virus(es). Most AIVs require adaptation to non-waterfowl/non-shorebird host to efficiently replicate. AIVs exist as a pool of closely related but slightly different viruses known as quasi-species. As susceptible members of a flock are infected, selection of viral genotype(s) within the pool of viral quasi-species occurs. A wild bird origin (WBO) North American LPAIV isolate, A/mallard/Maryland/1159/2006 (H5N1) was serially passaged 10-times in turkeys, quail, chickens or ducks to create four host adapted viruses originating from a common progenitor virus. Each species supported the serial passage the viruses. Infected turkeys displayed a significant increase (p<0.05) in clinical disease signs (respiratory disease) correlating with increasing passage number. A whole genome cDNA sequencing library was prepared from the parental WBO A/mallard/Maryland/1159/2006 (H5N1) LPAIV RNA and sequenced using an ultra high-throughput sequencing platform. Analysis of the passage 10 host-adapted virus consensus sequences revealed little to no genetic change, however, in depth analysis of single nucleotide polymorphism (SNPs) revealed establishment of SNPs present in the parental WBO strain as well as the discovery of additional SNPs not represented within the parental WBO LPAIV. The diversity of SNPs in the passage 10 host-adapted viruses were greater than that of the parental WBO strain with the greatest number of SNPs observed within the HA and polymerase genes (PB1, PB2, PA). Mean bird infectious dose50 (MBID50) studies were used to compare the passage 10 host-adapted virus dose required to sustain infection within a homologous host compared to the parental WBO LPAIV. Lower MBID50 were observed the in turkeys, quail, and ducks infected with the respective passage 10 host-adapted viruses. Any expansion of the host range outside of the reservoir host is the result of ability of the virus to expand its genetic profile within a host through multiple rounds of replication.