A Turkey-origin H9N2 Avian Influenza Virus Shows Low Pathogenicity but Different Within-Host Diversity in Experimentally Infected Turkeys, Quail and Ducks.

Edyta Świętoń,Krzysztof Śmietanka,Ewelina Iwan,Monika Olszewska-Tomczyk,Karolina Tarasiuk

doi:10.3390/v12030319

Abstract

Avian influenza virus (AIV) is a highly diverse and widespread poultry pathogen. Its evolution and adaptation may be affected by multiple host and ecological factors, which are still poorly understood. In the present study, a turkey-origin H9N2 AIV was used as a model to investigate the within-host diversity of the virus in turkeys, quail and ducks in conjunction with the clinical course, shedding and seroconversion. Ten birds were inoculated oculonasally with a dose of 106 EID50 of the virus and monitored for 14 days. Virus shedding, transmission and seroconversion were evaluated, and swabs collected at selected time-points were characterized in deep sequencing to assess virus diversity. In general, the virus showed low pathogenicity for the examined bird species, but differences in shedding patterns, seroconversion and clinical outcome were noted. The highest heterogeneity of the virus population as measured by the number of single nucleotide polymorphisms and Shannon entropy was found in oropharyngeal swabs from quail, followed by turkeys and ducks. This suggests a strong bottleneck was imposed on the virus during replication in ducks, which can be explained by its poor adaptation and stronger selection pressure in waterfowl. The high within-host virus diversity in quail with high level of respiratory shedding and asymptomatic course of infection may contribute to our understanding of the role of quail as an intermediate host for adaptation of AIV to other species of poultry. In contrast, low virus complexity was observed in cloacal swabs, mainly from turkeys, showing that the within-host diversity may vary between different replication sites. Consequences of these observations on the virus evolution and adaptation require further investigation.

Highlights

Influenza A viruses show the highest genetic diversity and the broadest host spectrum among the four known influenza virus types [1]
Evolution of viruses is a multifactorial process depending on the virus mutation rate, within-host replication dynamics, infection and transmission modes and other epidemiological and ecological factors [36,37,38,39]
It has been shown that avian influenza viruses evolve faster in poultry than in wild birds, which could be partially explained by differences in the ecology of wild birds and poultry resulting in distinct contact rates and transmission routes [40]

Summary

Introduction

Influenza A viruses show the highest genetic diversity and the broadest host spectrum among the four known influenza virus types [1]. A wide range of influenza viruses is found in birds, which can harbour 16 subtypes of HA (H1-H16) and 9 subtypes of NA (N1-N9) in almost all possible configurations [2]. Infections with LPAIV in wild birds are usually asymptomatic [6] but the clinical outcome in poultry varies and is highly dependent on host species. Chickens seem to be most resistant to LPAI infection among the gallinaceous poultry species [7]. Infected quail usually shed high amounts of virus in the absence of any clinical signs and mortality, it is thought that quail may support virus perpetuation and adaptation to other species of gallinaceous poultry [11,12]

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Results

Conclusion