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More than 23 million birds in 24 states have been affected by the ongoing bird flu outbreak as the highly contagious virus infects flock after flock.

The poultry industry, regulators and politicians have repeatedly assured consumers it is not a food safety issue. No human cases have been reported.

Highly transmissible bird viruses do, however, have the potential to do economic damage. The 2015 outbreak caused millions of dollars in losses. That episode caused the death of 50 million birds — including 9 million in Minnesota, the nation's leading turkey producer.

As of Wednesday, 21 sites in 11 Minnesota counties have reported infections, affecting more than a million birds, according to the state Board of Animal Health. Other than two backyard poultry operations, all of those have been turkey operations since the first reported infections on March 26.

"This is an active situation in Minnesota and other states across the country, and it is too early at this point to determine the outbreak's impact on the overall turkey industry," the National Turkey Federation said Tuesday. "To date, turkey losses have not reached the levels experienced in the 2015 outbreak, with approximately 1% of U.S. turkey production affected by avian influenza at this time."

Minnesota has more than 660 turkey farms that raise about 40 million birds per year.

Jennie-O Turkey Store, based in Willmar, Minn., said the virus has hit several of the Minnesota farms in its supply chain.

The brand, owned by Hormel Foods, said in a statement it "has been preparing for this situation and took extensive precautions to protect the health of the turkeys in its supply chain."

A U.S. Department of Agriculture emergency response team has been deployed to the state to assist farmers and help prevent further spread.

Here are answers to common questions about the outbreak.

What is bird flu?

The H5N1 highly pathogenic avian influenza virus — HPAI or simply bird flu — is a respiratory disease spread by a variety of bird species. Wild migratory birds are believed to be the primary source of spread across state lines. The first case of the current outbreak was reported at a commercial turkey farm in Indiana in February.

What is the risk to humans?

Very minimal. No human cases have been reported in the U.S. so far, though the Centers for Disease Control and Prevention say "some people may have job-related or recreational exposures to birds that put them at higher risk of infection."

"Infected birds shed avian influenza A viruses in their saliva, mucous and feces," the CDC says. "Human infections with bird flu viruses can happen when enough virus gets into a person's eyes, nose or mouth, or is inhaled."

The type of avian influenza spreading in the U.S. has infected a total of just 880 people worldwide in the past 25 years, according to the agency.

Can it reach the food supply in meat or eggs?

Unlikely. And if it did, cooking poultry and eggs to an internal temperature of 165 degrees kills the virus.

"Avian influenza is not transmissible by eating properly prepared poultry," the USDA says. "The chance of infected poultry or eggs entering the food chain is extremely low because of the rapid onset of symptoms in poultry as well as the safeguards USDA has in place, which include testing of flocks and federal inspection programs."

What happens when a flock is infected?

Behavior changes and sudden die-off can tip off a farmer that avian influenza has reached their flock. The Minnesota Poultry Testing Laboratory or the University of Minnesota Veterinary Diagnostic Laboratory will test samples, which are then confirmed by the USDA's National Veterinary Services Laboratories in Ames, Iowa.

Birds are quarantined and killed to prevent the virus from spreading, and human movement on and between farms is severely restricted. A six-mile control area around the site of the outbreak is monitored, and at least four weeks pass before barns can be restocked.

How are farmers affected financially?

The federal government spent $879 million responding to the 2015 outbreak — including $200 million in payments for lost birds, according to a USDA report.

The biggest shock to the industry could come from lower demand as consumers avoid poultry and eggs. Further hurting demand, prices for eggs are rising as egg-laying hens are killed in the outbreak, limiting supplies.

What about backyard chickens?

Backyard poultry owners need to follow biosecurity basics and report illness immediately. The Minnesota Board of Animal Health said it is most important to prevent exposure to wild waterfowl.

Neighbors worried about avian flu going unchecked on their block can call the Minnesota Avian Influenza Hotline at 1-833-454-0156.

What about wild birds?

The CDC says wild birds can be infected without appearing sick, and the following precautions should be taken:

  • Avoid direct contact with wild birds and observe them only from a distance.
  • Avoid contact with poultry that appear ill or have died.
  • Avoid contact with surfaces that appear to be contaminated with feces from wild or domestic birds.

Bird feeders pose a low risk of contamination, but extra precautions should be taken and waterfowl should not be fed for the time being.

How does this outbreak compare to 2015?

The deadliest avian flu outbreak in the United States claimed 50 million turkeys and chickens between December 2014 and June 2015. The majority of the infections occurred between April and May. About 12% of the country's egg-laying hens and 8% of turkeys grown for meat were killed by the virus or culled to prevent its spread, according to the USDA.

As the outbreak reaches its third month, the National Turkey Federation says "industry, USDA and state animal health officials are engaged in a coordinated effort to respond quickly to avian influenza incidences in commercial turkey flocks. Growers continue to focus on biosecurity and closely monitoring the health of flocks."

Can I help?

Report sick or dead birds to the Minnesota Avian Influenza Hotline: 1-833-454-0156.

Report sick or dead wild waterfowl or birds in groups of five or more to the Department of Natural Resources: 1-888-646-6367.

Flock owners and poultry workers can call the Minnesota Farm and Rural Helpline at 1-833-600-2670 or text FARMSTRESS to 898211.