LINCOLN, Neb. (DTN) -- Three more dairy herds in three additional Michigan counties have tested positive for highly pathogenic avian influenza, according to state officials, in tests confirmed by the USDA's National Veterinary Services Laboratory.

Earlier this week, HPAI was confirmed in dairy herds in North Carolina and South Dakota, bringing the total to eight states. The latest Michigan confirmations bring the total to 27 farms where a dairy herd contracted H5N1 avian influenza.

Officials with the Michigan Department of Agriculture and Rural Development said during a news conference on Friday that HPAI was detected in commercial dairy herds in Ionia, Isabella and Ottawa counties, bringing the number of affected Michigan herds to four.

The state announced on March 29 its first HPAI-positive herd in Montcalm County.

It had been previously reported that the first positive herd in Michigan had received cows from one of the infected Texas herds.

Michigan State Veterinarian Nora Wineland said on Friday that it was unclear whether there was a Texas connection to the new cases in Michigan.

"So, I think what we can say is our initial herd did have a history of movement of cattle from Texas," she said.

"Our other herds, we're still in the process of really understanding any kind of movements, both of cattle from perhaps other states as well as between herds within the state of Michigan. At this point, I would say we are still looking into that and do not have a definitive answer."

Wineland said the positive tests in Michigan have come primarily from large commercial herds of 500 or more animals.

Tim Boring, director of the Michigan Department of Agriculture and Rural Development, said it's unclear as to how the three additional Michigan herds were infected.

State officials are exploring what, if any, connection there might be between infected poultry and the dairies.

"We continue to work with a commercial (poultry) lot here in Michigan in Ionia County that has the virus on their farm," Boring said.

"As far as connection points there, we're continuing to evaluate what possible transmission mechanisms might have been. This is the same strain of the virus. So, both the dairy farms we're talking about here and that commercial poultry lot are highly pathogenic avian influenza. Still, a lot of questions remain around what those linkages might possibly look like."

TRANSMISSION INVESTIGATION

Wineland said scientists across the country continue to look at the possible methods for transmitting the virus.

"It's a national situation," she said. "So, we're seeing this same strain in wild birds that we're seeing in poultry that we're seeing in our dairies. And I think it's good to understand that you know people that study the whole genome sequence. So, the genetics of that virus are saying that it is not adjusted, adapted, whatever is the best term to use there to be more capable of affecting mammals than it was before. But, again, like the director said, that is something we are continuing to watch and study and pay attention to."

Wineland said tests performed on Michigan herds are finding the highest amount of the virus in milk samples. She said this may indicate milk is a vector to transmit the virus between dairy cows.

"The thought is that somehow the milk is involved in the transfer of the virus between cows and somehow also is involved in any transfers between farms," she said.

Michigan officials said farmers need to contact their veterinarians immediately if animals are showing clinical signs. This also allows scientists to get a better handle on how the virus is being transmitted.

The first cases of HPAI in cattle were confirmed March 25 by USDA, though Texas officials indicated cows at a pair of dairy farms were showing signs of illness earlier in the month.

Several other states also have banned or restricted the movement of dairy cattle. North Carolina and Tennessee suspended movement of cattle from affected herds in other states. Nebraska issued a restriction requiring a temporary permit for all breeding female dairy cattle from other states.

COMMERCIAL MILK SUPPLY SAFE

According to USDA, the Food and Drug Administration, and the Centers for Disease and Prevention, the commercial milk supply remains safe because of federal animal health requirements and pasteurization.

Federal experts continue to stress there is no concern about the safety of the commercial milk supply or that this circumstance poses any increased risk to consumer health.

In Michigan, state law requires pasteurization for any milk sold in stores. Pasteurization has continually proven to inactivate bacteria and viruses, like influenza, in milk.

"HPAI doesn't affect dairy cows the same way as it does with poultry," Wineland said.

"With proper veterinary care, cows are recovering. Biosecurity is the best line of defense. Still, we want to stress working with your veterinarian is fundamental for the recovery of affected dairy cows."

Michigan officials said dairies continue to be strongly encouraged to implement enhanced biosecurity measures to help prevent the spread of disease.

That includes limiting people coming onto dairies to employees and essential personnel only and following best management practices, including washing hands often.

Read more on DTN:

"HPAI in Dairy Cows Hits Two More States," https://www.dtnpf.com/…

Todd Neeley can be reached at todd.neeley@dtn.com

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