Washington - The United States is dealing with its worst outbreak of bird flu on record. More than 44 million chickens, turkeys and other birds have been culled since last December.
This is not the same avian influenza virus that has caused human infections in Africa, Asia and Europe. Migrating birds are believed to be responsible for some of the virus' spread and researchers are still studying how it is reaching poultry farms.
In the current outbreak, the US Department of Agriculture has confirmed bird flu in commercial and backyard flocks in 16 states so far.
Four states (Iowa, Minnesota, Wisconsin and Nebraska) have declared an emergency response to deal with the outbreak.
The H5N2 strain of the virus has been found in commercial and backyard flocks in 14 states so far: Arkansas, Idaho, Iowa, Kansas, Kentucky, Minnesota, Missouri, Montana, Nebraska, North Dakota, Oregon, South Dakota, Washington and Wisconsin.
The H5N8 strain has appeared in commercial and backyard flocks in California, Idaho, Indiana, Oregon and Washington.
In Canada, the H5N2 strain was confirmed in Ontario and British Columbia, and the H5N1 strain was confirmed in British Columbia.
Dozens of countries have imposed total or partial bans on U.S. poultry and egg imports since the outbreak of what is called highly pathogenic avian influenza (HPAI).
Each of the top 10 importers has introduced restrictions. Total bans have been imposed by China, South Korea and Angola, whose markets were valued at nearly $700m last year.
Top US poultry producing states of broiler chickens in 2014
Georgia: 1.414 billion, 15.5% of US total
Alabama: 1.140 billion, 12.5%
Arkansas: 1.029 billion, 11.3%
North Carolina: 855 million, 9.4%
Mississippi: 778 million, 8.5%
Meat-producing turkeys in 2014
Minnesota: 45 million, 19.1%of US total
Arkansas: 29 million, 12.3%
North Carolina: 28 million, 11.9%
Indiana: 19 million, 8.1%
Missouri: 16 million, 6.8%
Egg production in 2014
Iowa: 16.449 billion, 16.5% of US total
Ohio: 8.731 billion, 8.8%
Indiana: 7.747 billion, 7.8%
Pennsylvania: 7.570 billion, 7.6%
Texas: 5.109 billion, 5.1%