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By Karl Plume and Tom Polansek
CHICAGO, June 8 (Reuters) - The death of more than 46 million chickens and turkeys in a bird flu outbreak is opening a rare fissure within the usually tight-knit U.S. poultry industry, pitting farmers with infected flocks against those who so far largely have sidestepped the worst outbreak in U.S. history.
At issue: whether to vaccinate poultry against the highly pathogenic bird flu virus.
Hard-hit turkey producers in the Midwest say they will continue to urge the U.S. Department of Agriculture (USDA) to approve a vaccine to protect their flocks, even after the agency decided on Wednesday against releasing a vaccine it was developing because tests showed it was not effective enough.
Chicken farmers in states not yet hit by the bird flu, such as Mississippi, are lobbying against approval of a vaccination program without more testing and economic analysis. Many producers worry vaccinated birds could spread the virus, while exporters say a vaccination program could act as a trigger for rejection of U.S. poultry in foreign markets.
James Sumner, president of the USA Poultry and Egg Export Council, highlighted the economic risks of vaccinating birds but said the organization did not have an official position on whether USDA should approve a vaccination program.
"Certain segments of the industry certainly do want to vaccinate, but it comes with complications," he said. "I don't think there are too many countries that have vaccinated and found it successful for their industry."
The stakes in the U.S. decision on whether to approve a vaccine are particularly high for farmers who raise broiler chickens for meat. U.S. producers export about $5.7 billion worth of poultry and eggs each year, about three-quarters of which comes from the broiler industry.
The USA Poultry and Egg Export Council estimates about $600 million in trade losses in the first quarter of this year alone due to restrictions imposed by importing countries because of bird flu infections.
So far, most countries that have imposed restrictions due to the outbreak have restricted shipments from geographic areas with infections. However exporters worry that more buyers may impose nationwide bans on imports of U.S. poultry if a vaccine is used. The exact impact is unknown because the United States has never before used a vaccine to fight highly pathogenic bird flu.
The dispute over vaccination is unusual for the poultry industry, where chicken and turkey growers usually present a united front on issues involving regulation and trade.
The National Chicken Council, a trade group representing the broiler industry, asked the USDA in a letter last month to determine how the top 20 export markets for U.S. poultry would react to vaccine use before approving an immunization plan.
The group also said it was uncertain that a vaccine would reduce the number of infected flocks. Some poultry makers are concerned that inoculated birds might "shed" the live virus, putting other birds at risk of catching the fatal disease.
"We are opposed to using it without it being tested fully," Mike Cockrell, chief financial officer of Sanderson Farms Inc , the third largest U.S. poultry producer, said last week.
For a vaccination program to be effective, it would need to be part of a broader strategy, including improving disinfection methods on farms and swiftly killing infected flocks, said John Glisson, vice president of research for the U.S. Poultry and Egg Association.
Otherwise, it will be difficult to distinguish between flocks infected with the virus and those that are vaccinated.
"We know we can't just vaccinate the birds and live with the virus," Glisson said. "We've got to get rid of this virus."
The USDA has said it views the use of a vaccine as a last resort, preferring attempts to eliminate the virus by quarantining infected farms and culling birds there. The large death toll of birds in the current outbreak is partly because of culling.
Even so, scientists at the USDA's Southeast Poultry Research Laboratory in Georgia tested the vaccine that the USDA developed and found it to be about 60 percent effective on chickens. They are still evaluating its effectiveness in turkeys, according to the agency. The USDA said it will encourage the development of other vaccines and evaluate them when they are ready.
In poultry-rearing states hard hit by the virus, vaccination is viewed as an important tool.
"For us in Minnesota, the biggest turkey-producing area in the country, without that vaccine I worry about the future of the industry," said U.S. Representative Collin Peterson, a Minnesota Democrat and the ranking member on the House Agriculture Committee.
Farmers in Minnesota would like to begin vaccinating turkeys this summer in anticipation of a potential resurgence of infections when water fowl begin migrating south in the autumn, said Steve Olson, executive director of the Minnesota Turkey Growers Association. Bird flu has wiped out about 9 million birds in the state.
Wild birds are thought to be carriers of the virus, which also can be tracked onto poultry farms by people or trucks that come into contact with contaminated feces. It may also be carried into barns by wind blowing in contaminated dirt or dust. (Editing by Frances Kerry)