Evolution of H9N2 avian influenza virus in embryonated chicken eggs with or without homologous vaccine antibodies

Abstract

BackgroundVaccines constitute a unique selective pressure, different from natural selection, drives the evolution of influenza virus. In this study, A/Chicken/Shanghai/F/1998 (H9N2) was continually passaged in specific pathogen-free embryonated chicken eggs with or without selective pressures from antibodies induced by homologous maternal antibodies. Genetic mutations, antigenic drift, replication, and pathogenicity of the passaged virus were evaluated.ResultsAntigenic drift of the passaged viruses occurred in the 47th generation (vF47) under selective pressure on antibodies and in the 52nd generation (nF52) without selective pressure from antibodies. Seven mutations were observed in the vF47 virus, with three in PB2 and four in HA, whereas 12 mutations occurred in the nF52 virus, with three in PB2, two in PB1, four in HA, one in NP, one in NA, and one in NS. Remarkably, the sequences of the HA segment from vF47 were 100% homologous with those of the nF52 virus. Both the vF47 and nF52 viruses showed enhanced replication compared to the parental virus F/98, but higher levels of replication and pathogenicity were displayed by nF52 than by vF47. An inactive vaccine derived from the parental virus F/98 did not confer protection against challenges by either the vF47 or nF52 virus, but inactive vaccines derived from the vF47 or nF52 virus were able to provide protection against a challenge using F/98.ConclusionTaken together, the passage of H9N2 viruses with or without selective pressure of the antibodies induced by homologous maternal antibodies showed genetic variation, enhanced replication, and variant antigenicity. Selective pressure of the antibody does not seem to play a key role in antigenic drift in the egg model but may impact the genetic variation and replication ability of H9N2 viruses. These results improve understanding of the evolution of the H9N2 influenza virus and may aid in selecting appropriate vaccine seeds.

Effect of the Selection Pressure of Vaccine Antibodies on Evolution of H9N2 Avian Influenza Virus in Chickens

“…Previous studies have shown that serial passaging of the influenza virus in nonimmunized animals can lead to increased pathogenicity and transmission of the virus [13,[41][42][43]. Moreover, the infectivity of virus serially passaged without selection pressure of vaccine antibodies also increases [40,44]. In this experiment, the infectivity of progeny virus of the F/98 strain after serial passaging for more than 20 generations was obviously increased (P<0.01), which was in line with the previous research results.…”

“…In 2007-2010, h9.4.2.5 had become the advantageous popular strain [26,39]; after 2010, the h9.4.2.6 virus represented by A/chicken/Guangdong/FZH/2011 also appeared in southern China [4]. To control the infection and transmission of the H9N2 subtype avian influenza virus, a vaccination measure was taken in mainland China to control and prevent the virus [40]. At present, the H9N2 subtype avian influenza virus is still pervasive in most provinces of China.…”

Genetic Characteristics and Pathogenicity Analysis in Chickens and Mice of Three H9N2 Avian Influenza Viruses

“…However, most of the H9N2 viruses were not lethal for chickens, and these studies only detect the ability of these viruses to replicate in the respiratory tract and intestinal tract of chickens. It is still unclear whether these viruses could replicate in other organs [1,9,27,[32][33][34]. In the present study, we demonstrated that all of these viruses were generally shed in higher titers from the respiratory tract and the intestinal tract.…”

Effect of the Selection Pressure of Vaccine Antibodies on Evolution of H9N2 Avian Influenza Virus in Chickens

“…Previous studies have shown that serial passaging of the influenza virus in nonimmunized animals can lead to increased pathogenicity and transmission of the virus (Guarnaccia et al,2013,Li et al,2014,Murcia et al,2012,Pavulraj et al,2015. Moreover, the infectivity of virus serially passaged without selection pressure of vaccine antibodies also increases (Jin et al,2018,Shanmuganatham et al,2016. In this experiment, the infectivity of progeny virus of the F/98 strain after serial passaging for more than 20 generations was obviously increased (P<0.01), which was in line with the previous research results.…”