A strain of bird flu entered the Pacific Northwest in December and has been moving east ever since. (Reuters)

Maryland is banning poultry exhibits at state and county fairs and will quarantine out-of-state hatching eggs and chickens in hopes of preventing a bird flu outbreak that could be catastrophic for a key driver of the state economy.

Agriculture Secretary Joe ­Bartenfelder said the arrival of the virus in Maryland “could very well bring economic disaster to our largest agricultural sector,” which in 2013 produced nearly $1 billion in chicken meat and $52 million worth of eggs.

“I strongly encourage all flock owners and managers to take this disease as seriously as they have ever taken anything and to practice enhanced biosecurity at all times,” Bartenfelder said.

Bird flu, which is formally known as Highly Pathogenic Avian Influenza, is not known to threaten human health. But it can wipe out flocks of chickens within days, agriculture officials said.

The strain, which is carried by migratory waterfowl such as ducks and geese, entered the Pacific Northwest in December 2014 and has been spreading eastward, with 48 million birds affected in 15 states.

Officials said the bird flu virus does not survive in hot weather, so infections have declined over the summer. But animal-health experts expect the bug to reemerge during the fall migratory season, which starts in early September for Maryland.

To prevent the spread of the virus, state officials said there will be no chickens or other poultry on display after Aug. 25. The ban will affect the Maryland State Fair, which begins Aug. 28 in Baltimore County, and at least seven other county or local fairs.

Fairs that take place earlier in August, such as the Montgomery County Fair, can still have chickens, officials said.

Andrew McLean, who operates a farm with six chicken houses in Queen Anne’s County, said the new rules are unlikely to have much effect on Maryland’s poultry producers, many of whom receive their hatching eggs from certified clean sources and do not exhibit their birds at shows.

But the cost of not taking action, he said, would be devastating if farmers’ flocks became infected.

“Imagine not having any income for a year but still having all your payments,” McLean said. “Whatever we can do to minimize the risk, I’m all in favor of that.”

All hatching eggs and poultry that are brought into Maryland from outside the state will be quarantined and tested within 10 days if they do not come from certified clean sources, officials said. The quarantine order is in effect until at least the end of June.

The new rules do not affect poultry auctions, where state officials examine and test birds. However, the Agriculture Department said it will close down auctions if bird flu is suspected in the region.

Jenny Rhodes, another chicken farmer from Queen Anne’s County, said the threat of bird flu has made her extra vigilant about biosecurity measures, such as cleaning bird droppings from equipment, washing footwear before entering chicken houses and using dedicated clothing for working with her flock.

“Whatever we wear in the chicken houses, we don’t wear into town or anywhere else,” Rhodes said.

The measures taken by Maryland, which consistently ranks among the nation’s largest poultry producers, appear to be among the strictest in the Mid-Atlantic.

Delaware implemented a ban on waterfowl entries for poultry competitions at the Delaware State Fair that began Thursday, but the state has not imposed a similar prohibition on chickens.

Virginia has advised poultry operations not to allow unnecessary visitors and to take maximum biosecurity precautions with suppliers, veterinarians and others.

The agency has also asked flock owners to prevent their chickens from being exposed to flyovers or droppings from wild waterfowl.

And in North Carolina, the nation’s fifth-largest poultry producer, the state is requiring all poultry owners to register so that officials can warn them in case of infections near their properties. Those who own more than 200 chickens must also submit an outbreak plan.

A 2004 bird flu outbreak in Maryland forced the slaughter of nearly 330,000 chickens at a farm in Worcester County and prompted a quarantine on eight other farms in the area.

The outbreak also led to a restriction on farms located north of U.S. 50 on the Eastern Shore from using manure from chicken houses to fertilize their fields.