WASHINGTON, United States ( AFP ) – US farmers have been forced to kill almost 40 million chickens and other birds, causing egg prices to soar as a deadly version of the avian flu attacks the poultry industry.

An outbreak of a particularly infectious version of the bird flu, believed to come initially from wild ducks and geese, has spread into 15 US states and two Canadian provinces, requiring the mass slaughter of egg-laying chickens and turkeys in particular.

That has turned into an 80 percent surge in the wholesale price of eggs, and a more modest hike in turkey meat costs, which could last for the rest of the year even if the flu outbreak can be successfully contained, according to industry officials.

The midwest state of Iowa, the largest US egg producer, has seen some 25 million birds, mostly chickens for egg production, killed.

The state has declared a state of emergency against the disease, and after discovering avian flu on a 63rd farm, on Thursday banned any public exhibition of live birds, including at fairs, auctions, swap meets and other events.

“The scale of this outbreak has been unprecedented, so we think it is important we take every possible step to limit the chance that this disease will spread any further,” said Iowa Secretary of Agriculture Bill Northey.

The disease first surfaced last year in the far northwest state of Washington, apparently transmitted by wild birds.

Since then it has appeared in farms in 15 states, including some of those with the largest poultry industries.

Scientists describe the disease, known as H5N2, as a highly pathogenic version of the avian flu. It is different from the H5N1 flu now found widely in farms in Asia that has proven able to jump from poultry to humans and killed hundreds of people after it first surfaced in 2004.

The US Centers for Disease Control says the risk of H5N2 jumping to humans is “low at this time,” though it does not rule out the possibility.

Figures from the US Department of Agriculture show that more than 39 million birds had been infected by or exposed to the new strain of bird flu as of this week.

Canada too has also seen H5N2 outbreaks in flocks at farms in British Columbia and Ontario.

Dustin Vande Hoef, spokesman for the Iowa Department of Agriculture, said the pace of new infections has slowed and the state thinks the disease will soon be under control, helped by the arriving summer.

“We have had less infections the last couple of weeks… It’s certainly on the downhill side,” Vande Hoef told AFP.

“Warmer weather makes it harder for the disease to survive.”

But he said the process of cleaning and sterilizing poultry facilities, inspecting them, and then stocking them with new chickens, means the tighter supply could last until next year.

“It will take time to put birds back in there,” he said.

The US outbreak has added to a recent surge of infections by numerous strains of avian flu worldwide, which spurred the World Organization for Animal Health (OIE) to issue a general warning earlier this week.

“To prevent the disease from spreading, it is vital to implement OIE-recommended sub security measures in farms, in commerce and in live bird markets, disease surveillance and early detection,” the organization said.

“While the role of wild birds as reservoirs and vectors of the virus has been highlighted in these various epidemics, other factors of transmission, especially among poultry farms, could rise to prominence unless appropriate precautions are taken.”