22.03.2012

Three unique triple reassortant (TR) H3N2 influenza viruses bearing gene segments from 2009 pandemic H1N1 (pH1N1) in domestic turkeys were reported by a Canadian group in PLoS One.

Triple reassortant (TR) H3N2 influenza viruses cause varying degrees of loss in egg production in breeder turkeys. In this study TR H3N2 viruses isolated from three geographically separate breeder turkey farms in southern Ontario with a drop in egg production, were characterized. The eight gene segments of the virus isolated from the first case submission (FAV-003) were all of TR H3N2 lineage. The samples 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. The turkeys on the latter two farms had been vaccinated before the outbreak with the only vaccine approved in Canada against H3N2 influenza in turkeys, an H3N4 oil emulsion vaccine. 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. The authors note that close proximity of turkey and swine farms, which is thought to play a role in the epidemiology of TR H3N2 flu virus infection in turkeys, is common in the area where the tested farms are located.

Phylogenetic analysis of the HA and NA genes from FAV-009 and FAV-0010 showed that they are closely related to A/Swine/QC/126553/2010 (H3N2) and A/Swine/QC/1268883/2010 (H3N2) which were isolated from pigs with respiratory illness in Quebec. The latter H3N2 isolate from swine also has pandemic

H1N1 internal genes, but of a different assemblage than those found in FAV-009 and FAV-010. The other TR H3N2 virus (FAV-003) was closely related to other TR H3N2 viruses that were isolated from pigs in 2009 in Quebec. Although phylogenetic analysis shows that these viruses were likely introduced to turkeys from pigs, no  epidemiologic link was found between the farms.

In contrast to the chicken reproductive tract that contains only alpha 2-3-linked sialic acids receptors, turkeys may contain both alpha 2-3-linked and alpha 2-6-linked sialic acids receptors in their reproductive tract which could be involved in the attachment and replication of human and swine-like influenza viruses. This is the first time pH1N1/TR H3N2 reassortant viruses have been reported in domestic poultry.

 

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