Key result
Texas H5N3 isolate with a 28-amino acid deletion replicates better than other H5 strains in chickens.
Why the study?
Isolation of H5 subtype avian influenza viruses has been uncommon in US commercial poultry, with recent outbreaks requiring characterization to understand virus origins and adaptation.
Observational
The identification of a more chicken-adapted H5N3 virus in Texas highlights the need for ongoing surveillance of H5 subtype avian influenza in US poultry.
May signal greater H5N3 adaptation in US poultry; leaves open surveillance priorities pending confirmatory studies.
In the US, the isolation of H5 subtype avian influenza (AI) viruses has been uncommon in commercial chickens and turkeys, although sporadic isolations have been made from the live bird markets or its supply chain since 1986. In 2002, two different outbreaks of H5 AI occurred in commercial chicken or turkey operations. The first occurred in Texas and was identified as a H5N3 subtype AI virus. The second outbreak was caused by a H5N2 virus isolated from a turkey farm in California. In this study we analyzed recent H5 subtype AI viruses from different avian species and different sources in the US. Most recent H5 subtype isolates shared a high sequence identity and phylogenetically assorted into a separate clade from the Pennsylvania/83 lineage isolates. However, no established lineage was found within this clade and the recent H5 subtype isolates seemed to be the result of separate introductions from the wild bird reservoir. The Texas H5N3 isolate shared the lowest homology with the other recent isolates in the haemagglutinin gene and had a unique haemagglutinin cleavage site sequence of REKR/G (other recent isolates have the typical avirulent motif, RETR/G). Furthermore, this isolate had a 28 amino acid deletion in the stalk region of the neuraminidase protein, a common characteristic of chicken adapted influenza viruses, and may indicate that this virus had actually been circulating in poultry for an extended period of time before it was isolated. In agreement with genetic evidence, the Texas H5N3 isolate replicated better than other H5 isolates in experimentally infected chickens. The outbreak in Texas with a more chicken-adapted H5N3 virus underscores the importance of ongoing surveillance and control efforts regarding the H5 subtype AI virus in the US.
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Lee et al. (2004) conducted an observational in H5 subtype avian influenza. Texas H5N3 isolate vs. Other recent H5 isolates was evaluated on Genetic characteristics and replication in experimentally infected chickens. The Texas H5N3 isolate exhibited unique genetic features, including a 28 amino acid deletion in the neuraminidase stalk, and replicated better than other H5 isolates in infected chickens.