Comparative Pathogenicity and Transmissibility of the H7N9 Highly Pathogenic Avian Influenza Virus and the H7N9 Low Pathogenic Avian Influenza Virus in Chickens.

Hao Yu,Xumeng Ye,Kunpeng Zhang,Yun Guan,Peirong Jiao,Yong Wang,Xia Wang,Wenbo Wu,Wenqing Wang,Zhuoliang He

doi:10.3390/v11111047

Abstract

There were five outbreaks of H7N9 influenza virus in humans in China since it emerged in 2013, infecting >1000 people. The H7N9 low pathogenic influenza virus was inserted into four amino acids in the HA protein cleavage site to mutate into the H7N9 highly pathogenic virus. This emerging virus caused 15 outbreaks in chickens from the end of 2016 to date. Two H7N9 avian influenza virus (AIV) strains, A/chicken/Guangdong/A46/2013 (LPAIV) and A/chicken/Guangdong/Q29/2017 (HPAIV), were selected to compare the pathogenicity and transmissibility between H7N9 LPAIVs and HPAIVs in chickens. We inoculated 3- to 4-week-old specific-pathogen-free (SPF) chickens with 6 log10EID50/0.1 mL viruses via the ocular-nasal route and co-housed four chickens in each group. The inoculated chicken mortality rate in the A46 and Q29 groups was 1/5 and 5/5, respectively. Q29 virus replication was more efficient compared to the A46 virus in inoculated chickens. Infected chickens initiated viral shedding to naïve contact chickens through respiratory and digestive routes. Both viruses transmitted between chickens by naïve contact, but the Q29 virus had a higher pathogenicity in contact chickens than the A46 virus. Compared with early H7N9 LPAIVs, the pathogenicity and transmissibility of the emerging H7N9 HPAIV was stronger in chickens, indicating that H7N9 influenza virus may continue to threaten human and poultry health.

Highlights

Avian influenza is an infectious disease that is caused by avian influenza virus (AIV) and it infects poultry and various species of wild birds
These results indicated that both the A46 virus and the Q29 virus can be transmitted between chickens by naïve contact, but the Q29 virus had a higher pathogenicity in contact chickens compared to the A46 virus
In 2013, the first case of H7N9 low pathogenic influenza virus infection in a human was reported in East China

Summary

Introduction

Avian influenza is an infectious disease that is caused by avian influenza virus (AIV) and it infects poultry and various species of wild birds. AIV is a single-stranded negative-sense RNA virus belonging to the family Orthomyxoviridae and genus Influenzavirus A [1]. The virus contains eight gene segments encoding at least ten proteins, such as hemagglutinin (HA), neuraminidase (NA), polymerase acid (PA), polymerase basic 1 (PB1), PB2, nucleoprotein (NP), nonstructural 1 (NS1), NS2, matrix 1. 16 HA and nine NA subtypes of AIVs have been detected in wild birds and poultry all over the world [1,3,4,5]. According to the pathogenicity of the virus in chickens, AIV is classified into the highly pathogenic avian influenza virus (HPAIV) and the low pathogenic avian influenza virus (LPAIV).

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