Differential replication properties among H9N2 avian influenza viruses of Eurasian origin.

Rokshana Parvin,Antje Rueckner,Thomas W Vahlenkamp,Kristin Heenemann,Mohammad Y Halami,Awad A Shehata,Malgorzata Gac

doi:10.1186/s13567-015-0198-8

Rokshana Parvin, Antje Rueckner + Show 5 more

Open Access

https://doi.org/10.1186/s13567-015-0198-8

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Abstract

Avian influenza H9N2 viruses have become panzootic in Eurasia causing respiratory manifestations, great economic losses and occasionally being transmitted to humans. To evaluate the replication properties and compare the different virus quantification methods, four Eurasian H9N2 viruses from different geographical origins were propagated in embryonated chicken egg (ECE) and Madin-Darby canine kidney epithelial cell systems. The ECE-grown and cell culture-grown viruses were monitored for replication kinetics based on tissue culture infectious dose (TCID50), Hemagglutination (HA) test and quantitative real time RT-PCR (qRT-PCR). The cellular morphology was analyzed using immunofluorescence (IF) and cellular ELISA was used to screen the sensitivity of the viruses to amantadine. The Eurasian wild type-H9N2 virus produced lower titers compared to the three G1-H9N2 viruses at respective time points. Detectable titers were observed earliest at 16 h post inoculation (hpi), significant morphological changes on cells were first observed at 32 hpi. Few nucleotide and amino acid substitutions were noticed in the HA, NA and NS gene sequences but none of them are related to the known conserved region that can alter pathogenesis or virulence following a single passage in cell culture. All studied H9N2 viruses were sensitive to amantadine. The G1-H9N2 viruses have higher replication capabilities compared to the European wild bird-H9N2 probably due to their specific genetic constitutions which is prerequisite for a successful vaccine candidate. Both the ECE and MDCK cell system allowed efficient replication but the ECE system is considered as the better cultivation system for H9N2 viruses in order to get maximum amounts of virus within a short time period.

Highlights

Avian influenza H9N2 is a low pathogenic avian influenza virus (LPAIV) which in many countries continues to cause respiratory diseases, drop in egg production and increase in mortality among commercial domestic poultry and wild birds [1,2,3]
Comparison of hemagglutination (HA) titer The HA titer was calculated both from the harvested Allantoic fluids (AFs) and cell culture supernatants (CCSs) of embryonated chicken egg (ECE)- grown and cell culture-grown viruses, respectively
Efficient isolation and propagation of influenza viruses is important in epidemiological surveillance, study of hostpathogen interactions, diagnosis and vaccine production

Summary

Introduction

Avian influenza H9N2 is a low pathogenic avian influenza virus (LPAIV) which in many countries continues to cause respiratory diseases, drop in egg production and increase in mortality among commercial domestic poultry and wild birds [1,2,3]. H9N2 viruses become endemic in poultry in many Eurasian countries in some Asian and Middle Eastern countries [4]. Molecular genetic analyses of H9N2 viruses, isolated during the last two decades revealed that these viruses are highly evolving and a genetically diverse population [5]. Its extensive species tropism, distribution and ability to donate internal genes to the highly pathogenic H5 and H7 subtypes [11,12,13,14] evoke particular concerns.

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