Prior exposure to immunogenic peptides found in human influenza A viruses may influence the age distribution of cases with avian influenza H5N1 and H7N9 virus infections.

N Komadina,K Leder,S M Quiñones-Parra,K Kedzierska,S G Sullivan,J Mcvernon

doi:10.1017/s095026881900102x

Abstract

The epidemiology of H5N1 and H7N9 avian viruses of humans infected in China differs despite both viruses being avian reassortants that have inherited six internal genes from a common ancestor, H9N2. The median age of infected populations is substantially younger for H5N1 virus (26 years) compared with H7N9 virus (63 years). Population susceptibility to infection with seasonal influenza is understood to be influenced by cross-reactive CD8+ T cells directed towards immunogenic peptides derived from internal viral proteins which may provide some level of protection against further influenza infection. Prior exposure to seasonal influenza peptides may influence the age-related infection patterns observed for H5N1 and H7N9 viruses. A comparison of relatedness of immunogenic peptides between historical human strains and the two avian emerged viruses was undertaken for a possible explanation in the differences in age incidence observed. There appeared to be some relationship between past exposure to related peptides and the lower number of H5N1 virus cases in older populations, however the relationship between prior exposure and older populations among H7N9 virus patients was less clear.

Highlights

The influenza viruses cause significant respiratory tract infections and economic burden globally, due to yearly epidemics and intermittent pandemics [1, 2]
Given the variety of factors that may affect observed epidemiology between countries, we focus here on a comparison of human cases of avian H5N1 and H7N9 influenza viruses restricted to those occurring in China
This study examined the temporal patterns of circulation of H5N1 and H7N9 viral immunogenic peptides that were present in the NP, PB1 and M1 proteins found in human influenza viruses

Summary

Introduction

The influenza viruses cause significant respiratory tract infections and economic burden globally, due to yearly epidemics and intermittent pandemics [1, 2]. The 1997 and 2003 H5N1 as well as the 2013 H7N9 influenza viruses were avian reassortants that had inherited all six internal genes from an avian H9N2 virus common ancestor [10] Both H5N1 and H7N9 viruses cause severe disease in humans, the epidemiology in humans differs for each virus [9]. Given the variety of factors that may affect observed epidemiology between countries, we focus here on a comparison of human cases of avian H5N1 and H7N9 influenza viruses restricted to those occurring in China. Years Number of cases in first year of outbreak Gender differences Case fatality rate Presence of underlying medical conditions Urban residents Exposure to poultry. Experimental studies have identified a number of conserved CD8+ T cell immunogenic peptides between seasonal, pandemic and avian influenza viruses including H7N9 [21]. We hypothesise that differences in relatedness of peptides between the historical human strains and the two avian-emerged strains could in part explain the differences in age–incidence of disease observed due to H5N1 and H7N9 viruses

Methods

Results

Discussion