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. 2016 Jul 7:7:1066.
doi: 10.3389/fmicb.2016.01066. eCollection 2016.

Pathogenesis and Phylogenetic Analyses of Two Avian Influenza H7N1 Viruses Isolated from Wild Birds

Hongmei Jin  1 , Deli Wang  2 , Jing Sun  3 , Yanfang Cui  2 , Guang Chen  4 , Xiaolin Zhang  1 , Jiajie Zhang  1 , Xiang Li  1 , Hongliang Chai  1 , Yuwei Gao  5 , Yanbing Li  2 , Yuping Hua  1
Affiliations

Pathogenesis and Phylogenetic Analyses of Two Avian Influenza H7N1 Viruses Isolated from Wild Birds

Hongmei Jin et al. Front Microbiol. .

Abstract

The emergence of human infections with a novel H7N9 influenza strain has raised global concerns about a potential human pandemic. To further understand the character of other influenza viruses of the H7 subtype, we selected two H7N1 avian influenza viruses (AIVs) isolated from wild birds during routine surveillance in China: A/Baer's Pochard/Hunan/414/2010 (BP/HuN/414/10) (H7N1) and A/Common Pochard/Xianghai/420/2010 (CP/XH/420/10) (H7N1). To better understand the molecular characteristics of these two isolated H7N1 viruses, we sequenced and phylogenetically analyzed their entire genomes. The results showed that the two H7N1 strains belonged to a Eurasian branch, originating from a common ancestor. Phylogenetic analysis of their hemagglutinin (HA) genes showed that BP/HuN/414/10 and CP/XH/420/10 have a more distant genetic relationship with A/Shanghai/13/2013 (H7N9), with similarities of 91.6 and 91.4%, respectively. To assess the replication and pathogenicity of these viruses in different hosts, they were inoculated in chickens, ducks and mice. Although, both CP/XH/420/10 and BP/HuN/414/10 can infect chickens, ducks and mice, they exhibited different replication capacities in these animals. The results of this study demonstrated that two low pathogenic avian influenza (LPAI) H7N1 viruses of the Eurasian branch could infect mammals and may even have the potential to infect humans. Therefore, it is important to monitor H7 viruses in both domestic and wild birds.

Keywords: Avian influenza virus; H7N1; H7N9; pathogenic analyses; phylogenetic analysis.

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Figures

Figure 1
Figure 1
A phylogenetic tree based on the open reading frame sequences of the HA (A), NA (B), PB2 (C), PB1 (D), PA (E), NP (F), M (G), and NS (H) gene segments of two H7N1 AIVs. The two isolated H7N1 viruses are indicated by a closed circle and highlighted in purple. Human isolates are highlighted in red. Different lineages are highlighted in different colors. The trees were constructed using the neighbor-joining method of MEGA6.0 6 with 1000 bootstrap trials to assign confidence to the groupings.
Figure 1
Figure 1
A phylogenetic tree based on the open reading frame sequences of the HA (A), NA (B), PB2 (C), PB1 (D), PA (E), NP (F), M (G), and NS (H) gene segments of two H7N1 AIVs. The two isolated H7N1 viruses are indicated by a closed circle and highlighted in purple. Human isolates are highlighted in red. Different lineages are highlighted in different colors. The trees were constructed using the neighbor-joining method of MEGA6.0 6 with 1000 bootstrap trials to assign confidence to the groupings.
Figure 1
Figure 1
A phylogenetic tree based on the open reading frame sequences of the HA (A), NA (B), PB2 (C), PB1 (D), PA (E), NP (F), M (G), and NS (H) gene segments of two H7N1 AIVs. The two isolated H7N1 viruses are indicated by a closed circle and highlighted in purple. Human isolates are highlighted in red. Different lineages are highlighted in different colors. The trees were constructed using the neighbor-joining method of MEGA6.0 6 with 1000 bootstrap trials to assign confidence to the groupings.
Figure 1
Figure 1
A phylogenetic tree based on the open reading frame sequences of the HA (A), NA (B), PB2 (C), PB1 (D), PA (E), NP (F), M (G), and NS (H) gene segments of two H7N1 AIVs. The two isolated H7N1 viruses are indicated by a closed circle and highlighted in purple. Human isolates are highlighted in red. Different lineages are highlighted in different colors. The trees were constructed using the neighbor-joining method of MEGA6.0 6 with 1000 bootstrap trials to assign confidence to the groupings.
Figure 1
Figure 1
A phylogenetic tree based on the open reading frame sequences of the HA (A), NA (B), PB2 (C), PB1 (D), PA (E), NP (F), M (G), and NS (H) gene segments of two H7N1 AIVs. The two isolated H7N1 viruses are indicated by a closed circle and highlighted in purple. Human isolates are highlighted in red. Different lineages are highlighted in different colors. The trees were constructed using the neighbor-joining method of MEGA6.0 6 with 1000 bootstrap trials to assign confidence to the groupings.
Figure 1
Figure 1
A phylogenetic tree based on the open reading frame sequences of the HA (A), NA (B), PB2 (C), PB1 (D), PA (E), NP (F), M (G), and NS (H) gene segments of two H7N1 AIVs. The two isolated H7N1 viruses are indicated by a closed circle and highlighted in purple. Human isolates are highlighted in red. Different lineages are highlighted in different colors. The trees were constructed using the neighbor-joining method of MEGA6.0 6 with 1000 bootstrap trials to assign confidence to the groupings.
Figure 1
Figure 1
A phylogenetic tree based on the open reading frame sequences of the HA (A), NA (B), PB2 (C), PB1 (D), PA (E), NP (F), M (G), and NS (H) gene segments of two H7N1 AIVs. The two isolated H7N1 viruses are indicated by a closed circle and highlighted in purple. Human isolates are highlighted in red. Different lineages are highlighted in different colors. The trees were constructed using the neighbor-joining method of MEGA6.0 6 with 1000 bootstrap trials to assign confidence to the groupings.
Figure 1
Figure 1
A phylogenetic tree based on the open reading frame sequences of the HA (A), NA (B), PB2 (C), PB1 (D), PA (E), NP (F), M (G), and NS (H) gene segments of two H7N1 AIVs. The two isolated H7N1 viruses are indicated by a closed circle and highlighted in purple. Human isolates are highlighted in red. Different lineages are highlighted in different colors. The trees were constructed using the neighbor-joining method of MEGA6.0 6 with 1000 bootstrap trials to assign confidence to the groupings.
Figure 2
Figure 2
Viral titers of the two isolated H7N1 viruses in the organs of chickens (A) and ducks (B) at 3 dpi. Viral titers are shown as the mean ± standard deviation. The dashed line indicates the lower limit of viral detection.
Figure 3
Figure 3
Replication and virulence of the two isolated H7N1 viruses in mice: (A) Viral titers in the various tissues of the mice at 3 dpi. Viral titers are shown as the mean ± standard deviation. The dashed line indicates the lower limit of viral detection. (B) Weight changes in mice throughout the experiment. Weight changes are shown as the mean ± standard deviation. The weight changes of the CP/XH/420/10 and control groups differed significantly (P < 0.05). The BP/HuN/414/10 and control groups showed no significant difference (P > 0.05).
Figure 4
Figure 4
Representative histopathological changes in the organs of the experimental mice (A) inoculated with the BP/HuN/414/10 (H7N1) virus and (B–D) with the CP/XH/420/10 (H7N1) virus. (A) Pulmonary congestion and moderate broadening of the alveolar septum. (B) Granular degeneration of renal tubular epithelial cells. (C) Pulmonary congestion. (D) Mild granular degeneration of some liver cells.
Figure 5
Figure 5
The results of A/chicken/Jilin/HU/02 (H5N1) (A), A/Jilin/31/2005 (H1N1) (B), A/Baer's Pochard/Hunan/414/2010 (H7N1) (C), and A/Common Pochard/Xianghai/420/2010 (H7N1) (D) agglutination of different red blood cells. a: Chicken red blood cells (with α-2,3-linked sialic acid receptors and α-2,6-linked sialic acid receptors). b: Sheep red blood cells (with only α-2,3-linked sialic acid receptors). c: Chicken red blood cells treated with α-2,3-sialidase (with only α-2,6-linked sialic acid receptors). d: Chicken red blood cells treated with VCNA (no receptors).
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