Molecular and Antigenic Characterization of Reassortant H3N2 Viruses from Turkeys with a Unique Constellation of Pandemic H1N1 Internal Genes

Yohannes Berhane,Davor Ojkic,Wanhong Xu,Tamiko Hisanaga,John Pasick,Helen Kehler,Katherine Handel,Leo L M Poon

doi:10.1371/journal.pone.0032858

Yohannes Berhane, Davor Ojkic + Show 6 more

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https://doi.org/10.1371/journal.pone.0032858

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Journal: PLoS ONE	Publication Date: Mar 21, 2012
Citations: 32	License type: CC BY 4.0

Affiliation: University of Guelph, Canadian Food Inspection Agency

Abstract

Triple reassortant (TR) H3N2 influenza viruses cause varying degrees of loss in egg production in breeder turkeys. In this study we characterized TR H3N2 viruses isolated from three breeder turkey farms diagnosed with a drop in egg production. The eight gene segments of the virus isolated from the first case submission (FAV-003) were all of TR H3N2 lineage. However, viruses from the two subsequent case submissions (FAV-009 and FAV-010) were unique reassortants with PB2, PA, nucleoprotein (NP) and matrix (M) gene segments from 2009 pandemic H1N1 and the remaining gene segments from TR H3N2. Phylogenetic analysis of the HA and NA genes placed the 3 virus isolates in 2 separate clades within cluster IV of TR H3N2 viruses. Birds from the latter two affected farms had been vaccinated with a H3N4 oil emulsion vaccine prior to the outbreak. The HAl subunit of the H3N4 vaccine strain had only a predicted amino acid identity of 79% with the isolate from FAV-003 and 80% for the isolates from FAV-009 and FAV-0010. By comparison, the predicted amino acid sequence identity between a prototype TR H3N2 cluster IV virus A/Sw/ON/33853/2005 and the three turkey isolates from this study was 95% while the identity between FAV-003 and FAV-009/10 isolates was 91%. When the previously identified antigenic sites A, B, C, D and E of HA1 were examined, isolates from FAV-003 and FAV-009/10 had a total of 19 and 16 amino acid substitutions respectively when compared with the H3N4 vaccine strain. These changes corresponded with the failure of the sera collected from turkeys that received this vaccine to neutralize any of the above three isolates in vitro.

Highlights

Type A influenza viruses belong to the family Orthomyxoviridae and have a segmented genome composed of 8 single-stranded RNAs of negative sense [1]
Clinical submission # 1 (FAV-003) All 5 swab specimens that were submitted to National Centre for Foreign Animal Disease (NCFAD) on February 25, 2011 tested positive with the influenza A matrix real time RT-PCR assay developed by USDA [22]
Samples were inoculated into embryonating SPF chicken eggs with only one yielding virus after 2nd passage which did not hemagglutinate chicken red blood cells (CRBC)

Summary

Introduction

Type A influenza viruses belong to the family Orthomyxoviridae and have a segmented genome composed of 8 single-stranded RNAs of negative sense [1]. The HA protein is an important target of the host immune response and subtype specific anti-HA antibodies usually provide protection against infection with viruses of same HA subtype [4], new antigenic variants that result from the accumulation of point mutations (antigenic drift) within antigenic sites, frequently emerge in response to host immune pressure. This results in the appearance of antigenic variants within the same subtype that are capable of evading the host’s immune response [5,6]. This process leads to the appearance of new subtypes with dramatic changes in antigenicity [5,7]

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Conclusion