Submitted to: Avian Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/15/2004
Publication Date: 6/1/2004
Citation: Lee, C.W., Senne, D., Linares, J.A., Woolcock, P., Stallknecht, D., Spackman, E., Swayne, D.E., Suarez, D.L. 2004. Characterization Of Recent H5 Subtype Avian Influenza Viruses From U.S. Poultry. Avian Pathology June 2004, 33(3), p.288-297. Interpretive Summary: Avian influenza virus can cause a mild to deadly disease in poultry, including chickens and turkeys. The disease can be separated into low pathogenic and highly pathogenic avian influenza. The highly pathogenic form of the virus is not normally found in U.S. poultry, but the highly pathogenic form of the virus can mutate from the low pathogenic form of the virus. Although, there are 15 hemagglutinin subtypes of the virus which represent different surface proteins, only the H5 and H7 subtypes have been associated with the highly pathogenic form of the virus. Because of this association with these subtypes, greater interest in tracking all H5 and H7 influenza viruses are carried out. This paper describes some of the recent studies of H5 influenza viruses isolates in the last five years. Most isolates came from ducks and were determined to similar to wild bird influenza viruses. Wild birds are the natural host for avian influenza. Two outbreaks in chickens and turkeys were examined more carefully. A influenza virus from Texas was unusual. The virus was different sequence wise from the other isolates and had some markers for being adapted to chickens. The virus in animal studies to grow well in chickens and had caused some disease, but it was not highly pathogenic. No further isolations of this virus have been made in the U.S.
Technical Abstract: H5 subtype avian influenza viruses (AIVs) are commonly isolated from poultry in the U.S. and have been related to three highly pathogenic avian influenza outbreaks in North America. Wild birds are commonly infected with AIVs, and these viruses are routinely transmitted from this reservoir to poultry. Sporadic isolations of H5 influenza virus has been made from the U.S. live bird markets or its supply chain. However, isolation of H5 subtype AIVs has not been common in chickens and turkeys in the recent five years. In 2002, two different outbreaks of H5 AIV occurred in chickens and turkeys. The first occurred in Texas and was identified as a H5N3 subtype AIV. The second was caused by a H5N2 virus isolated from a turkey farm in California. Most recent H5 subtype isolates from different sources shared a high sequence identity and phylogenetically assorted into a separate clade from the Pennsylvania/83 lineage isolates. Compared to other recent H5 isolates, the Texas H5N3 isolate had many unique changes in the HA gene including the HA cleavage site sequence of REKR/G (other recent isolates have the RETR/G which is a typical avirulent motif). This HA cleavage site sequence for H5 viruses is unusual and potentially could be the minimum basic amino acid sequence required for the virus to be highly pathogenic. Furthermore, this isolate had a 24 amino acid deletion in the stalk region of the NA gene, a characteristic of other 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, which further supports the idea that it is better adapted to chickens.