Amino acid substitutions in the neuraminidase protein of an H9N2 avian influenza virus affect its airborne transmission in chickens

Abstract

Cases of H9N2 avian influenza virus (AIV) in poultry are increasing throughout many Eurasian countries, and co-infections with other pathogens have resulted in high morbidity and mortality in poultry. Few studies have investigated the genetic factors of virus airborne transmission which determine the scope of this epidemic. In this study, we used specific-pathogen-free chickens housed in isolators to investigate the airborne transmissibility of five recombinant H9N2 AIV rescued by reverse genetic technology. The results show that airborne transmission of A/Chicken/Shandong/01/2008 (SD01) virus was related to the neuraminidase (NA) gene, and four amino acid mutations (D368E, S370L, E313K and G381D) within the head region of the SD01 NA, reduced virus replication in the respiratory tract of chickens, reduced virus NA activity, and resulted in a loss of airborne transmission ability in chickens. Similarly, reverse mutations of these four amino acids in the NA protein of r01/NASS virus, conferred an airborne transmission ability to the recombinant virus. We conclude that these four NA residues may be significant genetic markers for evaluating potential disease outbreak of H9N2 AIV, and propose that immediate attention should be paid to the airborne transmission of this virus.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-014-0142-3) contains supplementary material, which is available to authorized users.

A small-scale study on airborne transmission of H9N2 avian influenza virus under field conditions

“…These results showed that the chicken flocks infected by H9N2 AIV form and transmit viral aerosols. In addition, the results support previously published papers where exposure to H9N2 AIV aerosols is considered an important route of airborne transmission within chicken flocks [25][26][27].…”

Prevalence and diversity of H9N2 avian influenza in chickens of Northern Vietnam, 2014

“…This deletion, although minor compared to the 20 + amino acid deletions found recently in the N1 of HPAI H5N1 viruses, has been shown experimentally to increase the pathogenicity of H9N2 viruses in chickens and mice, and has become predominant in Chinese H9N2 circulation (94.8% of viruses since 2013) ( Sun et al, 2013 ). Although the Vietnamese NA genes had a number of additional molecular markers of virulence and airborne transmission in mammals and poultry ( Lv et al, 2015 ; Z. Zhang et al, 2011 ) (Table S1), they did not have any known molecular markers of oseltamivir resistance, and thus probably remain susceptible to the drug ( Gubareva, 2004 ).…”

A Global Perspective on H9N2 Avian Influenza Virus

“…One of the key molecular markers that facilitates adaptation of an AIV from wild aquatic birds to poultry is the deletion of amino acids from the stalk domain of NA, which have been shown to mediate the switch to respiratory tropism in chickens [77,78]. There is good evidence to suggest that many LPAIV strains transmit by the airborne route, the oral-faecal route and the waterborne route [15,75,79]. However, the favoured mechanism of transmission between individuals varies by host species and viral strain.…”

“…H9N2 viruses appear to have intrinsically more stable HAs compared to AIVs of the H5 and H7 subtype, in a similar range to early H1N1pdm09 viruses [135]. Furthermore, several adaptive mutations have been identified in field viruses that allow them to transmit by an airborne route between chickens, it is thought these would probably have the added effect of allowing more efficient transmission between humans as well [79,150].…”