A new strain of a highly pathogenic bird flu known as H7N9 has surfaced at a poultry farm in Mississippi where chickens are raised for breeding. The finding of the new strain came as researchers separately reported a potentially positive development: Exposure to human seasonal flu may confer some immunity to H5N1 bird flu. The new strain found in Noxubee County, Miss., was confirmed March 12 and all of the roughly 46,000 birds either died or were euthanized after the infection spread, according to the U.S. Department of Agriculture’s Animal Plant Health Inspection Service and Mississippi’s Board of Animal Health. None of the birds entered the food supply.

The United States reported the first outbreak of the deadly H7N9 bird flu on a poultry farm since 2017, as the country continues to grapple with another bird flu strain that has infected humans and caused egg prices to hit record highs. The spread of avian influenza, commonly called bird flu, has ravaged flocks around the world, disrupting supply and fuelling higher food prices. Its spread to mammals, including dairy cows in the U.S., has raised concerns among governments about a risk of a new pandemic. The strain that has caused most damage to poultry in recent years and the death of one person in the U.S. is the H5N1. The H7N9 bird flu virus has proved to have a high death rate for humans worldwide killing 616 people, or 39%, of the 1,568 people infected worldwide since it was first detected in 2013 in China, the World Health Organisation said.

The infection of 47,654 commercial broiler-breeder chickens was confirmed on March 13 by the World Organization for Animal Health (WOAH). Samples of the flock were tested at the Mississippi Veterinary Research & Diagnostic Laboratory and came back positive for highly pathogenic avian influenza, the State of Mississippi Board of Animal Health announced in a press release on March 12. The affected area has been quarantined and birds on the property have been depopulated to prevent spread. None of the birds from the flock have entered the food system, according to the Mississippi board.

The virus, which has a high fatality rate in humans, was detected at a Mississippi poultry farm.

U.S. reports 1st outbreak of deadly H7N9 bird flu since 2017. Different strain killed 1 person in U.S., and devastated flocks. Latest outbreak detected on a farm of 47,654 commercial broiler breeder chickens in Noxubee, Miss.