Avian influenza infections could continue in fall, next spring

Published on May 13, 2015
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The highly pathogenic H5 avian influenza viruses now in U.S. poultry flocks could have continued effects during the next year of wild bird migrations.

Nearly 16 million birds were expected to be killed or depopulated so far because of flock infections with an H5N2 influenza virus strain that had spread to at least 13 states as of April 29. Another highly pathogenic avian influenza virus, an H5N8 strain, had spread to a few Western U.S. commercial flocks containing about 250,000 birds.

Highly pathogenic H5 avian influenza virus strains caused infections in 74 commercial turkey flocks, which contained 4.2 million turkeys, by late April. About 3.3 million of those turkeys were in Minnesota, which had 61 confirmed infections.

Dr. John Clifford, chief veterinary officer for the Department of Agriculture, said the H5 avian influenza viruses have become adapted to wild waterfowl and may cause outbreaks in fall 2015 and spring 2016. The USDA Animal and Plant Health Inspection Service is studying pathways the viruses can use to enter poultry barns and is working with industry to mitigate risk over the summer.

The avian influenza viruses affected a greater number of chickens than turkeys, although far more turkey farms than chicken farms had infections.

APHIS figures indicated that, from December 2014 through April 2015, highly pathogenic H5N2 and H5N8 avian influenza viruses had affected 100 commercial or backyard flocks that together contained 15.8 million birds, about 11.5 million of which were on chicken farms. Affected premises had been quarantined prior to depopulation to prevent spread of the disease, APHIS information states.

Of the 86 commercial flocks with infections, 73 turkey flocks and 10 chicken flocks were affected by H5N2 influenza virus. Only one chicken flock and one turkey flock had H5N8 influenza virus infections.

Dr. Clifford said the USDA would work with industry and state governments to develop strategies, and that could include expanded vaccine use. He noted that option was only one under consideration.

Asked about potential changes to physical structures on farms, he said he wanted to avoid hurrying into decisions and find out whether any investments into structures would reduce risk.

Dr. Clifford doesn’t expect the avian influenza viruses will cause long-term consequences in future generations of chickens and turkeys. But he expressed concern about the uncertainty of how long the highly pathogenic viruses will remain in wild waterfowl and when less-pathogenic strains will again be the more common strains.