Genetic Characterization and Pathogenicity of H7N7 and H7N9 Avian Influenza Viruses Isolated from South Korea

Abstract

H7 low pathogenic avian influenza viruses (LPAIVs) can mutate into highly pathogenic avian influenza viruses (HPAIVs). In addition to avian species, H7 avian influenza viruses (AIVs) also infect humans. In this study, two AIVs, H7N9 (20X-20) and H7N7 (34X-2), isolated from the feces of wild birds in South Korea in 2021, were genetically analyzed. The HA cleavage site of the two H7 Korean viruses was confirmed to be ELPKGR/GLF, indicating they are LPAIVs. There were no amino acid substitutions at the receptor-binding site of the HA gene of two H7 Korean viruses compared to that of A/Anhui/1/2013 (H7N9), which prefer human receptors. In the phylogenetic tree analysis, the HA gene of the two H7 Korean viruses shared the highest nucleotide similarity with the Korean H7 subtype AIVs. In addition, the HA gene of the two H7 Korean viruses showed high nucleotide similarity to that of the A/Jiangsu/1/2018(H7N4) virus, which is a human influenza virus originating from avian influenza virus. Most internal genes (PB2, PB1, PA, NP, NA, M, and NS) of the two H7 Korean viruses belonged to the Eurasian lineage, except for the M gene of 34X-2. This result suggests that active reassortment occurred among AIVs. In pathogenicity studies of mice, the two H7 Korean viruses replicated in the lungs of mice. In addition, the body weight of mice infected with 34X-2 decreased 7 days post-infection (dpi) and inflammation was observed in the peribronchiolar and perivascular regions of the lungs of mice. These results suggest that mammals can be infected with the two H7 Korean AIVs. Our data showed that even low pathogenic H7 AIVs may infect mammals, including humans, as confirmed by the A/Jiangsu/1/2018(H7N4) virus. Therefore, continuous monitoring and pathogenicity assessment of AIVs, even of LPAIVs, are required.

Prevalence, Seroprevalence and Risk Factors of Avian Influenza in Wild Bird Populations in Korea: A Systematic Review and Meta-Analysis

“…Studies that reported both prevalence and seroprevalence had a risk of bias, assessed by sorting each result. Prevalence studies that used samples from the entire nation [ 8 , 17 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ] or major migratory bird habitats [ 2 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ] determined that the sampling frame was properly chosen, as samples were taken from within the pertinent regions to calculate the prevalence therein. The sampling frame made for the studies whose primary goal was to identify the characteristics of isolated AIVs [ 64 , 65 , 66 , 67 ] was judged to be at a high risk of bias because the isolation rate reported in the studies was constrained to a particular region.…”

“…Seven primary studies that evaluated the prevalence of AIVs were judged to have a low bias in the sampling method, owing to proper capture methods from randomized wild birds [ 2 , 41 , 42 , 43 , 48 , 50 , 57 ]. All studies, except for two [ 59 , 66 ] that did not describe the isolation method in detail, recorded the condition of the samples by examining them with the proper techniques, such as RT-PCR [ 2 , 8 , 17 , 41 , 42 , 43 , 44 , 48 , 49 , 50 , 51 , 52 , 54 , 55 , 56 , 58 , 60 , 61 , 62 , 65 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 ], rRT-PCR [ 53 , 63 , 64 , 75 , 76 ], or HA tests [ 41 , 42 , 46 , 47 , 57 , 77 ]. All investigations, except for 12 studies [ 8 , 46 ,…”

“…All investigations, except for 12 studies [ 8 , 46 , 55 , 57 , 58 , 59 , 65 , 66 , 67 , 68 , 75 , 77 ], had read the experimental results with distinguishing criteria. Prevalence studies with small [ 56 , 57 , 58 , 59 , 64 , 65 , 66 , 67 , 68 , 69 , 71 , 73 , 74 ] and large sample sizes [ 2 , 8 , 17 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 60 , 61 , 62 , 63 , 70 , 72 , 75 , 76 ] were differentiated according to adequate sample size (1000 samples).…”

“…All studies unambiguously stated the number of examined samples and the number of positive or virus-detected samples. Studies that assessed prevalence in subgroups subdivided into sampling month [ 46 , 60 , 64 , 68 , 70 , 72 ], sampling year [ 2 , 8 , 48 , 49 , 51 , 54 , 55 , 72 ], province [ 17 , 41 , 42 , 43 , 51 , 58 , 59 , 60 , 68 , 75 ], and bird species [ 42 , 43 , 46 , 48 , 49 , 50 , 51 , 52 , 57 , 58 , 59 , 68 , 75 ] allowed for comparisons between the study sample and the population of interest. A low coverage bias was determined in prevalence studies [ 2 , 41 , 42 , 43 , 48 , 50 , 52 , 60 , 72 , 75 ] that used a similar sample number for each distinct subgroup.…”

“…A low coverage bias was determined in prevalence studies [ 2 , 41 , 42 , 43 , 48 , 50 , 52 , 60 , 72 , 75 ] that used a similar sample number for each distinct subgroup. Otherwise, coverage bias was assessed as high [ 8 , 17 , 46 , 49 , 51 , 54 , 55 , 57 , 58 , 59 , 64 , 68 , 70 ].…”