H7 avian flu hits UK; US chickens exposed to H7N3

Jun 4, 2008 (CIDRAP News) – Animal health officials in England yesterday announced that chicken deaths at a farm in Oxfordshire were caused by an H7 form of avian influenza, while a poultry company in Arkansas reported that chickens at a large commercial farm tested positive for antibodies to a low-pathogenic H7N3 strain of avian flu.

In an update today, England's Department for Environment, Food and Rural Affairs (DEFRA) said further laboratory tests have shown that the H7 strain found in birds at the farm in Banbury, about 80 miles northwest of London, is highly pathogenic and added that more tests are underway to determine the neuraminidase (N) type.

Authorities have launched a detailed epidemiologic investigation to determine how the birds became infected and if the latest findings have any links to previous outbreaks, DEFRA said.

Control zones were established yesterday within 3 and 10 kilometers around the outbreak site, and officials are considering if wider measures are needed, the DEFRA statement said.

Hilary Benn, secretary of state for Environment, Food, and Rural Affairs, said in a statement today that avian flu suspicions were first reported on Jun 2 following deaths in a laying flock and reduced egg production. The United Kingdom's National Farmers' Union said today that the family-run free-range poultry farm contained a flock of 25,000 chickens, which is slated for culling.

England's last avian flu outbreak involved the highly pathogenic H5N1 strain, which hit wild swans at a sanctuary on the country's southwestern coast in early January. Outbreaks involving low-pathogenic H7 strains occurred in May 2006 (eastern England) and May 2007 (Wales and northwestern England).

Meanwhile, Tyson Foods, based in Springdale, Ark., announced in a press release yesterday that routine preslaughter tests on breeder hens at one of its farms in northwestern Arkansas showed the birds had antibodies to H7N3 avian flu.

The 15,000 birds showed no signs of illness but were to be culled and disposed of as a precautionary measure, the Tyson statement said.

The company said it would increase avian influenza surveillance within a 10-mile radius of the area, including on breeder farms that supply birds to Tyson.

"The increased surveillance is in addition to Tyson's existing testing program, which involves the company checking birds for avian influenza before they leave the farm," Tyson said.

Frank Jones, associate director for extension at the Center for Excellence for Poultry Science at the University of Arkansas at Fayetteville, said 10 to 12 low-pathogenic avian flu infections occur in the state each year, the Arkansas Democrat Gazette reported today. He said migratory geese could have brought the low-pathogenic strain to northwestern Arkansas, where it could have spread to the breeder hens.

"Typically these things happen in spring and fall when we get waterfowl migration. There's been a lot of waterfowl that have come through," Jones told the newspaper.

Last September a highly pathogenic strain of H7N3 struck a commercial poultry operation in Saskatchewan, and both highly pathogenic and low-pathogenic types were involved in outbreaks in British Columbia in 2004.

The last reported H7N3 outbreaks in the United States occurred in 2004 at three Texas farms.

A recent report in the Proceedings of the National Academies of Science suggested that North American avian flu viruses of the H7 subtype are becoming more like human flu viruses in their ability to attach to host cells, which might mean they are becoming more likely to infect humans. H7 infections in humans have typically caused only mild conjunctivitis, but a Dutch veterinarian died of an H7N7 infection in 2003.

See also:

Jun 4 statement from Hilary Benn

Jun 3 DEFRA press release

Jun 3 Tyson press release

May 28 CIDRAP News story "Some avian flu H7 viruses growing more humanlike"

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