After a relatively quiet summer and fall, highly pathogenic avian influenza has once again made its way into Michigan and Ohio poultry operations, according to the U.S. Centers for Disease Control.

December has been a tough month. In Michigan, four Ottawa County commercial poultry operations tested positive, while Ohio’s Darke County reported one.

In Ottawa County, Avian flu was detected on a 75,500-head commercial turkey operation Dec. 23, followed by a Dec. 27 outbreak in the same county with 113,200 head, according to the CDC.

On Dec. 30, the Michigan Department of Agriculture and Rural Development announced one backyard flock from Jackson County and two commercial poultry facilities in Ottawa County also tested positive. The size and type of flocks have not yet been released.

Ohio’s Darke County operation had 1 million commercial egg layers. Earlier, Dec. 19, Greene County had a backyard flock test positive.

The infections are the first in Michigan poultry since May, when the state managed the largest outbreak of the disease. Ohio had only a couple backyard flocks test positive in February this year, but in December 2023, Ohio lost more than 4.5 million birds to the disease.

The disease is found in an array of wildlife and domestic animals — most recently affecting cats — and was first detected in a Michigan backyard flock in February 2022. To date, 66 human cases of HPAI have been confirmed, according to the CDC, including six Michigan farmworkers who have all recovered.

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HPAI is a highly contagious virus that spreads in various ways from flock to flock, including by wild birds, through contact with infected animals, by equipment, and on the clothing and shoes of farmworkers. The affected premises are under quarantine, and the birds will be depopulated to prevent disease spread.

Avian flu has claimed more than 7 million birds in Michigan (the majority in 2024) and more than 10.5 million in Ohio. The national outbreak, which started in February 2022, continues and has now claimed almost 129 million birds nationwide. There has been a surge of infections in December across the country, with 16.8 million birds affected, more than the three previous months combined.

Dairy infections continue

While the poultry infections were quieted for several months, Michigan continues to battle the disease in dairy operations, where it was first discovered in March 2024. Of the 30 dairy herds affected, the latest were Oct. 14 in Clinton County and Sept. 9 in Shiawassee County. No cattle have died as a result of infection.

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Ohio had one dairy operation confirmed with HPAI in April.

In Michigan, there are 12 dairy operations — including two in Ottawa and Isabella counties that tested HPAI-positive as far back as April 12 — still taking measures to rid the disease and striving to obtain “unaffected status.”

The virus continues to spread on farms. It is now in more than 900 dairies in 16 states, according to the CDC. A different strain of the H5N1 virus has also been confirmed in an Oregon pig.

Regardless of the species, biosecurity remains the best tool to combat HPAI, says MDARD Director Tim Boring, who sent a letter to dairy producers Nov. 25, outlining the next steps to safeguard the industry and its products.

Nationwide milk testing

As a result of the expanding scope of HPAI, USDA is directing nationwide, mandated milk testing of bulk tanks at the farm level, milk silos at processing plants, or some combination of the two in all states across the country to understand the prevalence of the virus in America’s dairy herd. “The sampling process should have minimal impact to your dairy,” Boring writes.

Mutation of the virus, possibly allowing it to spread between people — which it currently doesn’t — remains a top concern.

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“Mutated forms of the virus may develop the ability to rapidly spread between people and cause more serious disease, significantly threatening human health,” Boring writes. “From conversations with so many of you, I know human health and the safety of you, your family and your staff remains your highest priority.”

Biosecurity measures, he says, are vital in helping ensure the health of Michigan’s domestic animals, as well as the health of the general public.

“Since this disease is capable of affecting animals and the people who care for them, it is important for farmworkers to continue using personal protective equipment to protect themselves and their loved ones,” says Dr. Natasha Bagdasarian, Michigan’s chief medical executive. “Preventing spread from animals to humans is vital if we want to limit the impact of this virus.”