Abstract
The study presents molecular characterization of H9N2 avian influenza (AI) isolates from field outbreaks in turkeys that occurred in Poland in 2013–2014. Sequences of all gene segments of one isolate from 2013 (A/turkey/Poland/14/2013(H9N2)) and two isolates from 2014 (A/turkey/Poland/08/2014(H9N2), A/turkey/Poland/09/2014(H9N2)) were obtained and analyzed in search of the phylogenetic relationship and molecular markers of zoonotic potential or increased pathogenicity. All gene segments were shown to originate from the wild bird reservoir and the close relationship of the analyzed isolates proved the link between the outbreaks in 2013 and 2014. However, remarkable molecular differences between isolates from 2013 to 2014 were identified, including mutation in the HA cleavage site (CS) leading to conversion from the PAASNR*GLF to the PAASKR*GLF motif and truncation of the PB1-F2 protein. Additionally, T97I substitution in the PA protein in A/turkey/Poland/08/2014 was detected which can be responsible for enhanced activity of viral polymerase in mammalian cells. However, experimental infection of mice with both isolates from 2014 showed their low pathogenicity, and no statistically significant differences in virus replication were observed between the viruses. Nevertheless, these findings indicate the dynamic evolution of H9N2 in the field emphasizing the need for monitoring of the situation in terms of H9N2 AI in Europe.
Highlights
Avian influenza virus (AIV) is an avian pathogen characterized by high diversity resulting from a high mutation rate and segmented genome enabling an exchange of genes in a reassortment event [1]
A close relationship with H10N7 from seals was observed for the PA gene (Fig. 2S in Electronic Supplementary Material (ESM)) indicating that H9N2 and H10N7 viruses share a common ancestor for both genes
The H9N2 subtype is one of the most common AIV occurring in poultry in the world
Summary
Avian influenza virus (AIV) is an avian pathogen characterized by high diversity resulting from a high mutation rate and segmented genome enabling an exchange of genes in a reassortment event [1]. The AIV genome consists of eight negative—sense single—stranded RNA segments coding for at least 11 viral proteins [2]. The two new subtypes H17N10 and H18N11 have been detected in bats, but so far they have not been found in birds [3, 4]. The natural reservoir for all AIV subtypes is wild aquatic birds, mainly Anseriformes and Charadriiformes [5]. There have been many cases of introduction of low pathogenicity (LP) AIV of various subtypes from the wild bird reservoir to poultry, usually resulting in transient outbreaks [6].
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