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.
Highlights
Cases of poultry infected with H9N2 avian influenza virus (AIV) have occurred repeatedly in many countries since its isolation in America in 1966 [1-4]
NA is important for aerosol transmission of H9N2 AIV in chickens To determine whether NA influences SD01 transmission in chickens, we first tested two recombinant viruses: recombinant SD01 virus recovered using reverse genetics; and r01/NASS virus, in which the NA of virus SD01 was replaced by that of SS94 (Figure 1A)
These results indicate that recombinant virus recombinant SD01 (rSD01) was detected in the air and transmitted by aerosols between chickens, but recombinant virus r01/NASS, in which the NA of virus SD01 was replaced by that of virus SS94, was not detected in the air and was not aerially transmitted
Summary
Cases of poultry infected with H9N2 avian influenza virus (AIV) have occurred repeatedly in many countries since its isolation in America in 1966 [1-4]. H9N2 AIV mainly infected feral birds and wild ducks in South America, and were unable to form a stable lineage in poultry [5,6]. H9N2 AIV infection of chickens, turkeys, pheasants, and domestic ducks has been reported throughout Asia, the Middle East, Europe and Africa from 1995 to 1997 [5,7-9]. H9N2 AIV isolated from diseased chickens in Guangdong province in 1994, represented the first documented case of H9N2 AIV in mainland China, and since 1998 the virus has spread widely [10-13]. It was considered a low pathogenic AIV, H9N2 caused high morbidity and mortality in poultry when co-infected with other pathogens [3,14]. It was reported that H9N2 AIV had crossed the species barrier, infecting humans in Hong Kong and Guangzhou, China [15,16]
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