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 / Updated  / Source: NBC News
By Maggie Fox

An Iowa farm that has more than 5 million chickens has been hit by H5N2 bird flu, a deadly virus that can wipe out flocks within days.

Iowa state health officials said the outbreak affected a large flock of egg-laying hens — the largest commercial U.S. flock to be hit by the virus since it first showed up in the United States late last year.

“All the birds on the site will be euthanized. The site is also quarantined,” said Dustin Vande Hoef, a spokesman for the Iowa Department of Agriculture.

Experts think wild birds flying from Asia are carrying the virus, one of many different types of avian influenza. This strain has never been known to infect human beings.

Ducks, especially, can carry avian influenza viruses without getting sick and they can spread them in their droppings.

“These virus strains can travel in wild birds without those birds appearing sick. People should avoid contact with sick/dead poultry or wildlife,” the Iowa Department of Agriculture said in a statement.

“These virus strains can travel in wild birds without those birds appearing sick."

“If contact occurs, wash your hands with soap and water and change clothing before having any contact with healthy domestic poultry and birds.”

There are dozens of strains of avian influenza but, until late last year, U.S. flocks had been free of the highly pathogenic strains that can kill domestic chickens, turkeys and other poultry in a matter of hours. Now a dozen states have reported infections.

It’s bad news for the farms, which must act quickly to slaughter all the birds in an affected flock, destroy the carcasses and disinfect and quarantine the facility. Then, health officials must test domestic and wild birds in the area to make sure the virus is not still around.

While experts say cooked chicken and eggs cannot transmit H5N2, the standard procedure is to destroy all potentially affected birds and eggs.

Bird flu fears grow

April 21, 201501:17

"There is no reason to avoid any food. All poultry is processed under federal or state inspection," USDA advises in a statement.

So far, it’s not a major blow to the U.S. poultry industry. Last year, the U.S. produced about 9.2 billion broiler chickens, about 95 billion eggs and 235 million turkeys, according to USDA.

"There is no reason to avoid any food. All poultry is processed under federal or state inspection."

H5N2 has been reported in Arkansas, Idaho, Kansas, Minnesota, Missouri, Montana, North Dakota, Oregon, South Dakota, Washington and Wisconsin. It’s also been seen in Canada.

On Monday Wisconsin declared an emergency and activated the state’s National Guard to help disinfect trucks leaving affected facilities there.

While the H5N2 outbreaks are only affecting birds, avian influenza viruses can and do infect people and this adds a level or urgency to controlling any outbreak.

The World Health Organization says more than 780 people in 16 countries are known to have been infected with H5N1 since 2003 and more than 400 of them have died. A second strain called H7N9 has infected 622 people since 2013 and killed 227 of them.

H5N1 is actively infecting people in Egypt now. The virus doesn’t spread easily from person to person and almost all of those infected have had close contact with birds. They’re often small family flocks and people who get infected have handled the birds, slaughtered them or collected eggs.

Flu is a mutation-prone virus and there are hundreds of strains. Even with precise-sounding names such as H5N1, there can be a large degree of genetic variation. Scientists are watching for mutations and other genetic changes that can make a virus strain more likely to infect people and poultry.