Updated

A strain of bird flu (search) has been found at four live chicken markets in northern New Jersey, just days after outbreaks at two farms in Delaware led to the destruction of thousands of birds.

New Jersey health officials stressed that the findings are not unusual for the state's live poultry markets and said the strain is not known to be harmful to humans.

"To the best of our knowledge, it's been a recurring problem for years," said Ed Wengryn, field representative for the New Jersey Farm Bureau (search). "It's not contagious to humans. Humans can't get it by being exposed to it or eating it."

Nancy Halpern, the state veterinarian, said the markets likely got the virus from one of the many farms and distributors who supply them. New Jersey has about 35 live chicken markets across the state.

No birds have died from it in New Jersey, according to Halpern, who said avian influenza can contaminate markets via truck tires, people's feet, bird crates or through bird-to-bird transmission.

There is no reason to order the destruction of birds in New Jersey like the ones in Delaware, officials said.

"There's a vast difference in the scenarios we're looking at," Halpern said in a conference call for reporters. "In Delaware, you have commercial flocks affected. Hence, they were depopulated to prevent further spread.

"In the state of New Jersey, we do not have a broiler industry and further we've only documented it in our live bird markets and only a few of them," Halpern said.

Markets found to be infected are instructed to sell off all birds, and then clean and sanitize all cages and equipment before reopening.

Officials said the strain found in New Jersey is the same one found at two farms in Delaware since last week. The strain is not related to the virulent variety of avian influenza that is blamed for the deaths of at least 19 people in Vietnam and Thailand.

In Delaware, the disease was found last week on a farm operated by an independent grower. On Tuesday, Delaware agriculture officials announced that tests confirmed avian flu on a second farm, saying it creates a "serious situation" for the region's poultry industry.

Even before the announcement Tuesday, China joined Poland, Japan, Malaysia, Singapore and South Korea in banning U.S. poultry imports because of the previous discovery. Hong Kong had banned the import of live birds and poultry from Delaware only. Russia also temporarily banned Delaware imports.