STARKVILLE, Miss. -- Until an avian flu vaccine for chickens or other alternative is federally approved, commercial poultry operations in the U.S. will have to keep “stamping out” entire flocks with a confirmed case to prevent further exposure -- just like one in Noxubee County recently had to do.

On March 12, the Mississippi Board of Animal Health reported the detection of highly pathogenic avian influenza, or HPAI, in a commercial broiler breeder chicken flock -- the state’s first reported case in 2025. The World Health Organization reported that the culling operation led to the slaughter of 47,654 chickens.

Stamping out is a term for culling an entire flock, which federal policy dictates must be done in the event of a confirmed infection. The most common bird flu strain in the current outbreak is H5N1, but the strain at the Noxubee County facility was identified as H7N9 -- the first report of this avian flu strain since 2017.

According to the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, or USDA-APHIS, the H7N9 virus detected in Noxubee County is a North American virus originating from wild birds and is not related to the Eurasian H5N1 clade 2.3.4.4b virus currently circulating in the U.S.

Samples from the flock were tested at the Poultry Research and Diagnostic Laboratory, or PRDL, part of the Mississippi Veterinary Research and Diagnostic Laboratory System, and results were confirmed at the National Veterinary Services Laboratory in Ames, Iowa. PRDL is housed within the Mississippi State University College of Veterinary Medicine but located in Pearl.

PRDL director Dr. Natalie Armour Manginsay said avian influenza viruses are characterized according to the hemagglutinin (H) and neuraminidase (N) glycoproteins, which project from the surface of the virus. There are 16 different H subtypes and 9 different N subtypes.

“The surface structure of the H5N1 and H7N9 viruses differ because they have different combinations of these glycoproteins on their surface, and this makes them ‘look’ different to the immune system,” Manginsay said. “Unlike other avian influenza viruses, H5 and H7 avian influenza viruses have the potential to mutate from low- to highly pathogenic. The H7N9 virus detected in this broiler breeder flock and the H5N1 virus that has caused outbreaks in poultry and other birds globally are highly pathogenic, meaning that these viruses have the potential to cause high mortality and devastating losses in poultry.”

Since the HPAI outbreak began in 2022, more than 166 million birds from 776 commercial and 884 backyard flocks have been affected as of March 21.

In February, the USDA announced a $1 billion effort toward combating avian flu and lowering egg prices, including $100 million toward vaccine research. The American Association for the Advancement of Science reported in February that the USDA had granted a conditional license to animal medicine producer Zoetis, but widespread use would require federal approval.

Manginsay said culling of flocks leads to questions about animal welfare and the sustainability of continuing to depopulate large numbers of chickens, but the $1 billion federal commitment will go toward identifying solutions for those concerns.

“Vaccination of poultry has not been allowed in the U.S., but vaccines are commercially available outside of the U.S.,” she said. “Multiple studies found high-potency HPAI vaccines matched to the field virus to be effective. They can protect birds from illness and death and can increase resistance to disease while reducing virus shedding.

“But there are a lot of concerns around the use of vaccines in poultry,” Manginsay added, “especially from the broiler industry, which is very concerned about the potential loss of export markets as some trading partners would most likely currently not accept vaccinated products.”

While the latest Mississippi case applies to broilers, HPAI detections and mortality rates are roughly 10 times more common at layer farms -- more than 74 million layer hens and 6.8 million broiler chickens were culled from 2022 to 2024, according to USDA statistics.

Jonathan Moon, a commercial poultry specialist with the Mississippi State University Extension Service, said shorter grow-out times and more frequent production cycles of broilers make them easier and faster to replace than layers.

“Most of the time, commercial egg layers are kept for extended periods of time on large farms, so there are greater numbers of birds in a centralized location that have to be eradicated once they test positive. This makes them tougher and much more time-consuming to replace,” Moon said. “Broiler farms, including broiler breeder farms, are spread out over a larger area, so the infection site doesn’t have as many birds to cull.”

The USDA reported the national average price for a dozen eggs as of March 14 was nearly 40% cheaper than a week before. The average on that day was $4.15 compared to $6.85 on March 7. The average price per dozen on Feb. 21 was $8.15. On March 21, the average was $3.27 per dozen.

Find more on avian influenza and biosecurity measures online at https://extension.msstate.edu/avian-flu. Report sick or dead birds to the Mississippi Board of Animal Health online at https://www.mbah.ms.gov/.