H7N7 Avian Influenza Virus Mutation from Low to High Pathogenicity on a Layer Chicken Farm in the UK.

Alexander M P Byrne,Caroline J Warren,Stephen Essen,Scott M Reid,Alejandro Núñez,Susan Ridout,Ian H Brown,Anita Puranik,Ana B Obeso Prieto,Sharon M Brookes,Amanda H Seekings,Marek J Slomka,Jill Banks,Vanessa Ceeraz

doi:10.3390/v13020259

Alexander M P Byrne, Caroline J Warren + Show 12 more

Open Access

https://doi.org/10.3390/v13020259

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Journal: Viruses	Publication Date: Feb 8, 2021
Citations: 9	License type: CC BY 4.0

Affiliation: Animal and Plant Health Agency, Manchester Airport

Abstract

Avian influenza virus (AIV) subtypes H5 and H7 are capable of mutating from low to high pathogenicity strains, causing high mortality in poultry with significant economic losses globally. During 2015, two outbreaks of H7N7 low pathogenicity AIV (LPAIV) in Germany, and one each in the United Kingdom (UK) and The Netherlands occurred, as well as single outbreaks of H7N7 high pathogenicity AIV (HPAIV) in Germany and the UK. Both HPAIV outbreaks were linked to precursor H7N7 LPAIV outbreaks on the same or adjacent premises. Herein, we describe the clinical, epidemiological, and virological investigations for the H7N7 UK HPAIV outbreak on a farm with layer chickens in mixed free-range and caged units. H7N7 HPAIV was identified and isolated from clinical samples, as well as H7N7 LPAIV, which could not be isolated. Using serological and molecular evidence, we postulate how the viruses spread throughout the premises, indicating potential points of incursion and possible locations for the mutation event. Serological and mortality data suggested that the LPAIV infection preceded the HPAIV infection and afforded some clinical protection against the HPAIV. These results document the identification of a LPAIV to HPAIV mutation in nature, providing insights into factors that drive its manifestation during outbreaks.

Highlights

Avian Influenza (AI) caused by subtypes H5 and H7 is a notifiable avian disease (NAD) and a severe threat to the poultry industry globally, whilst the emergence of novel avian influenza virus (AIV) strains from wild bird reservoirs is a constant threat to animal and human health
The infected premises (IP) was a family-run business located in a poultry-dense area in the county of Lancashire in the northwest of England (Figure 1A,B), containing 170,000 laying hens housed in ten sheds
Evidence based on the clinical picture, laboratory results, epidemiological investigations and expert advice were considered in order to estimate the time of incursion and subsequent spread of virus during this H7N7 high pathogenicity AIV (HPAIV) outbreak in the United Kingdom (UK)

Summary

Introduction

Avian Influenza (AI) caused by subtypes H5 and H7 is a notifiable avian disease (NAD) and a severe threat to the poultry industry globally, whilst the emergence of novel avian influenza virus (AIV) strains from wild bird reservoirs is a constant threat to animal and human health. From 1959 to 2017, the United Kingdom (UK) had 11 outbreaks of low pathogenicity AIV (LPAIV, subtypes H5 and H7) and 13 outbreaks of high pathogenicity AIV (HPAIV) [1,2,3,4] These have included two LPAIV to HPAIV mutational events of the H7N7 subtype in layer chickens, occurring in 2008 [4] and 2015 [5]. Acquisition of HA CS alterations in LPAIV to become HPAIV occurs in part due to the insertion of basic amino acids [1] These insertions make the HA proteolytic CS more accessible to ubiquitous intracellular proteases, allowing for systemic spread of the virus within the host [1]. Observing this mutation on a single premises during an outbreak is rare and three other UK H7 LPAIVs

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