Origin and molecular characterization of the human-infecting H6N1 influenza virus in Taiwan

In June 2013, the first human H6N1 influenza virus infection was confirmed in Taiwan. However, the origin and molecular characterization of this virus, A/Taiwan/2/2013 (H6N1), have not been well studied thus far. In the present report, we performed phylogenetic and coalescent analyses of this virus and compared its molecular profile/characteristics with other closely related strains. Molecular characterization of H6N1 revealed that it is a typical avian influenza virus of low pathogenicity, which might not replicate and propagate well in the upper airway in mammals. Phylogenetic analysis revealed that the virus clusters with A/chicken/Taiwan/A2837/2013 (H6N1) in seven genes, except PB1. For the PB1 gene, A/Taiwan/2/2013 was clustered with a different H6N1 lineage from A/chicken/Taiwan/ A2837/2013. Although a previous study demonstrated that the PB2, PA, and M genes of A/Taiwan/2/2013 might be derived from the H5N2 viruses, coalescent analyses revealed that these H5N2 viruses were derived from more recent strains than that of the ancestor of A/Taiwan/2/2013. Therefore, we propose that A/Taiwan/2/2013 is a reassortant from different H6N1 lineages circulating in chickens in Taiwan. Furthermore, compared to avian isolates, a single P186L (H3 numbering) substitution in the hemagglutinin H6 of the human isolate might increase the mammalian receptor binding and, hence, this strain's pathogenicity in humans. Overall, human infection with this virus seems an accidental event and is unlikely to cause an influenza pandemic. However, its co-circulation and potential reassortment with other influenza subtypes are still worthy of attention.

Prolonged excretion of a low-pathogenicity H5N2 avian influenza virus strain in the Pekin duck

H5N2 strains of low-pathogenicity avian influenza virus (LPAIV) have been circulating for at least 17 years in some Mexican chicken farms. We measured the rate and duration of viral excretion from Pekin ducks that were experimentally inoculated with an H5N2 LPAIV that causes death in embryonated chicken eggs (A/chicken/Mexico/2007). Leghorn chickens were used as susceptible host controls. The degree of viral excretion was evaluated with real-time reverse transcriptase-polymerase chain reaction (RRT-PCR) using samples from oropharyngeal and cloacal swabs. We observed prolonged excretion from both species of birds lasting for at least 21 days. Prolonged excretion of LPAIV A/chicken/Mexico/2007 is atypical.

Molecular analysis of an avian influenza virus isolate of H5N2 subtype from parrot / 病毒学报

In 2005, an avian influenza virus stain was isolated from Parrot in Guangdong, which was then genotyped as H5N2 subtype and designated as A/Parrot/Guangdong/268/2005. According to the current OIE definition on the low-pathogenicity of avian influenza virus, the strain was recognized as a low pathogenic avian influenza virus due to the presence of one basic amino acid residue at the HA cleavage site. Some molecular characteristics of the virus, such as potential glycosylation sites in HA and NA, receptor binding sites of HA, and drug resistance site of NA, showed no variations. To analyze molecular evolution of this strain, we selected the sequences of H5N2 subtype AIVs from GenBank and established the phylogenetic trees. Our results indicated that this strain shared the highest homologies with the H5N2 LPAI isolate A/Pheasant/NJ/1355/1998-like. Phylogenic analysis revealed the isolate, together with A/Chicken/Pennsylvania/1/1983 (H5N2), belonged to America lineages and clustered with A/Pheasant/NJ/1355/1998-like.

Analysis of the amino acid changes of the hemagglutinin of H5 avian influenza virus / 病毒学报

We introduced 38 single-point amino acid changes into the hemagglutinin (HA) protein of the reassortmented A/Duck/Mongolia/54/01 (H5N2) strain by a PCR random mutation method. The percentage of amino acid changes on the HA domain that did not abrogate hemadsorption activity was calculated to be 89%. Changes in the amino acids of the HA2 domain were observed to be about half of those in the HA1 domain of these mutants. We assumed that amino acid changes in the HA1 domain afforded more flexibility in maintaining the functions of the HA protein than did those in the HA2 domain. Changes at two positions allowed the mutants to have same characteristics with respect to HA function despite the difference in the substituted amino acid. The results suggested that the effect on hemadsorption activity of an amino acid change on the HA protein primarily depends on the position rather than the species of substituted amino acid. An amino acid change at residue 122 from Trp to Arg and 179 from His to Arg resulted in the loss of hemadsorption activity of the HA protein. Site 122 is near the antibody binding site A, and site 179 is in the receptor binding domain (RBD) of HSHA. So that we suggest residue position 179 or 122 is very important to maintain the structure of RBD or antigenic site of H5HA. Position 4 in HA1 changed from Cys to Arg and position 148 in HA2 changed from Cys to Tyr also resulted in the loss of hemadsorption activity of the HA protein. Cys plays an important role in maintaining the structure of HA protein by means of S-S bonds. 3 potential glycosylation sites (Asn-X-Ser/Thr) were lost in our experiment that did not lose the hemadsorption activity of HA. Some interesting positions need to be analyzed more finely. Some amino acid changes identified in vitro experiment may serve as molecular markers for assessing the pandemic potential of H5N1 field isolates.