Emergence and Evolution of Avian H5N2 Influenza Viruses in Chickens in Taiwan

Abstract

Sporadic activity by H5N2 influenza viruses has been observed in chickens in Taiwan IMPORTANCE H5N2 avian influenza viruses first appeared in chickens in Taiwan in 2003 and caused a series of outbreaks afterwards. Phylogenetic analyses show that the chicken H5N2 viruses have H5 and N2 genes that are closely related to those of a vaccine strain originating from Mexico in 1994, while the contemporary duck H5N2 viruses in Taiwan belong to the Eurasian gene pool. The unusually high similarity of the chicken H5N2 viruses to the Mexican vaccine strain suggests that these viruses might have been introduced to Taiwan by using inadequately inactivated or attenuated vaccines. These chicken H5N2 viruses are developing varying levels of pathogenicity that could lead to significant consequences for the local poultry industry. These findings emphasize the need for strict quality control and competent oversight in the manufacture and usage of avian influenza virus vaccines and indicate that alternatives to widespread vaccination may be desirable.

Hemagglutinin-Neuraminidase Balance Influences the Virulence Phenotype of a Recombinant H5N3 Influenza A Virus Possessing a Polybasic HA 0 Cleavage Site

“…To illustrate, a H5N2 virus isolated from a broiler flock and two live bird markets in Texas in 2004 was phenotypically low pathogenic, although possessing the HA 0 cleavage site PQRKKR/ GLF and hence genotypically HPAIV (7). Discordant results between molecular and in vivo tests used to characterize virus patho- genicity were retrospectively recognized for other H5 field virus isolates (8,9), as well as non-H5/H7 viruses that had been engineered to contain polybasic HA 0 cleavage sites (25,26,27). For example Stech et al (26) showed that inserting a polybasic cleavage site identical to that of HPAI A/chicken/Italy/8/98 (H5N2) into the HA of the LPAI A/duck/Ukraine/1/63 (H3N8) virus was not sufficient to immediately transform it into a highly pathogenic virus, despite the fact that it was able to replicate in tissue culture in the absence of exogenous trypsin.…”

“…During receptor mediated endocytosis of the virus, a low-pH-induced conformational change of the HA takes place, and this allows the fusion peptide to initiate the merging of the viral envelope with host endosomal membranes, a step necessary for influenza virus infectivity (5). Even though a polybasic HA 0 cleavage site is considered to be the dominant virulence determinant of HPAI H5 and H7 viruses (reviewed in reference 6), there have been instances where it has not been sufficient to confer a highly pathogenic phenotype (7,8,9). This implies that the evolution of a LPAI virus to a HPAI virus must involve additional changes in the other gene segments.…”

Genetic characterization of highly pathogenic H5 influenza viruses from poultry in Taiwan, 2015

“…The sequences obtained have been deposited in GenBank (accession numbers KT388441-KT388712). Phylogenetic analysis, as described previously (Lee et al, 2014b), was performed using these full genome sequences and closely related sequences from GenBank, GISAID and the publicly available government website (http://ai.gov.tw/index.php?id=720), which gave the sequences of the 16 H5 viruses isolated by the Council of Agriculture (COA), Taiwan during the recent outbreaks.…”

“…Six of these H5N2 chicken isolates belonged to the Mexican/95-like H5N2 viruses circulating in Taiwan since 2003, which obtained their internal genes from the enzootic chicken H6N1 lineage (Lee et al, 2014b).…”

Antigenic Analyses of Highly Pathogenic Avian Influenza A Viruses

“…Extensive reassortments have replaced the internal genes and NA, but the HA genes descend from an ancestor that resembles a virus that was used for vaccine manufacturing in Mexico. It has been postulated that incompletely inactivated poultry vaccines may have resulted in the introduction of the exotic virus into Japan and Taiwan (Lee et al 2014a). …”