A 20-Amino-Acid Deletion in the Neuraminidase Stalk and a Five-Amino-Acid Deletion in the NS1 Protein Both Contribute to the Pathogenicity of H5N1 Avian Influenza Viruses in Mallard Ducks

Abstract

Since 2003, H5N1-subtype avian influenza viruses (AIVs) with both a deletion of 20 amino acids in the stalk of the neuraminidase (NA) glycoprotein (A−) and a deletion of five amino acids at positions 80 to 84 in the non-structural protein NS1 (S−) have become predominant. To understand the influence of these double deletions in the NA and NS1 proteins on the pathogenicity of H5N1-subtype AIVs, we selected A/mallard/Huadong/S/2005 as a parental strain to generate rescued wild-type A−S− and three variants (A−S+ with a five-amino-acid insertion in the NS1 protein, A+S− with a 20-amino-acid insertion in the NA stalk, and A+S+ with insertions in both NA and NS1 proteins) and evaluated their biological characteristics and virulence. The titers of the AIVs with A− and/or S− replicated in DEF cells were higher than that of A+S+, and the A−S− virus exhibited a replication predominance when co-infected with the other variants in DEF cells. In addition, A−S− induced a more significant increase in the expression of immune-related genes in peripheral blood mononuclear cells of mallard ducks in vitro compared with the other variants. Furthermore, an insertion in the NA and/or NS1 proteins of AIVs resulted in a notable decrease in virulence in ducks, as determined by intravenous pathogenicity index, and the two insertions exerted a synergistic effect on the attenuation of pathogenicity in ducks. In addition, compared with A+S+ and A+S−, the A−S+ and A−S− viruses that were introduced via the intranasal inoculation route exhibited a faster replication ability in the lungs of ducks. These data indicate that both the deletions in the NA stalk and the NS1 protein contribute to the high pathogenicity of H5N1 AIVs in ducks.

Betacoronavirus Adaptation to Humans Involved Progressive Loss of Hemagglutinin-Esterase Lectin Activity

“…Of broader relevance, they provide a general paradigm for dynamic, catalysis-driven virus-sialoglycan interactions in relation to host selectivity. This notion is supported by observations for influenza A viruses, where neuraminidase (NA) activity toward multivalent substrates varies with differences in the length of the stalk domain and positively correlates with NA size (Castrucci and Kawaoka, 1993;Els et al, 1985), where NA catalytic activity is modulated by the absence or presence of a second Sia-binding site (Uhlendorff et al, 2009;Varghese et al, 1997) and where changes in NA stalk length and NA lectin affinity have been implicated in host specificity (Blumenkrantz et al, 2013;Castrucci and Kawaoka, 1993;Lai et al, 2012;Li et al, 2014;Matrosovich et al, 1999;Munier et al, 2010;Uhlendorff et al, 2009;Varghese et al, 1997). These observations can be readily interpreted in the context of our data and model proposed.…”

Loss of Fitness of Mexican H7N3 Highly Pathogenic Avian Influenza Virus in Mallards after Circulating in Chickens

“…Two changes in NP, M105V and S377N, have been repeatedly found in several independent studies as being associated with increased pathogenicity in chickens and adaptation in chickens and turkeys (30,33,35,37,38). Some studies report that deletions in either NA or NS are associated with an increase in pathogenicity in avian species (28,38,66). However, no deletions were observed in the Mexican H7N3 viruses.…”

Stop-codon variations in non-structural protein NS1 of avian influenza viruses

“…NS segments with this deletion, which are easier to track than the C-terminal truncations, are predominant in currently circulating H5N1 viruses and have spread to several non-H5N1 viruses. 20,21 The work by Abdelwhab et al is therefore one of the studies that could enhance our understanding of the flow of influenza virus genomic segments within and between the viral pools, in the wild avifauna reservoir, in gallinaceous poultry and in mammals.…”