U.S. authorities no longer ruling out cow-to-cow transmission of avian influenza

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Editor’s note: Updated with CDC confirmation of a human HPAI case in Texas.

U.S. animal health authorities say they cannot rule out cow-to-cow transmission of highly pathogenic avian influenza (HPAI) after detecting bird flu in dairy herds in another three states.

The U.S. Department of Agriculture’s National Veterinary Services Laboratories (NVSL) has confirmed the presence of HPAI in a Michigan dairy herd that recently received cows from a farm in Texas. The department says “presumptive positive test results” have also been received for additional herds in New Mexico, Idaho, and Texas, after confirmations in two herds in Texas and two in Kansas early last week.

“Spread of symptoms among the Michigan herd also indicates that HPAI transmission between cattle cannot be ruled out,” says a joint statement issued by USDA, Food and Drug Administration, and Centers for Disease Control and Prevention (CDC) on March 29.

The CDC also announced on April 1 that a person exposed to one of the infected herds in Texas has tested positive for the HPAI virus, with the main symptom being eye redness. While people with close or prolonged exposure to infected animals face a greater risk of infection, the CDC says the risk to the general public is still low.

HPAI has not been found in dairy cattle in Canada to date, according to an April 1 update from Alberta Milk and a subsequent emailed statement from the Canadian Food Inspection Agency.

“The CFIA has not detected HPAI in dairy cattle or other livestock in Canada,” an agency spokesperson tells RealAgriculture. “We are monitoring the situation closely.”

The new developments mean there is a need to heighten biosecurity measures on Canadian dairy farms now, says Alberta Milk, noting Dairy Farmers of Canada is working with the Canadian Food Inspection Agency and other experts on specific Canadian recommendations for heightened vigilance and biosecurity on Canadian farms.

One of the symptoms in U.S. herds has been reduced milk production, but affected animals have recovered after isolation with little to no associated mortality reported, the federal U.S. agencies say.

Initial testing is also not showing any changes to the virus that would make it more transmissible to humans, say U.S authorities. The virus found in Michigan is very similar to the wild bird strain confirmed in Texas and Kansas (H5N1, Eurasian lineage goose/Guangdong clade 2.3.4.4b.)

The USDA is also advising veterinarians and producers to practice good biosecurity, test animals before necessary movements, minimize animal movements, and isolate sick cattle from the herd.

As for food safety, the agencies say there is no concern about the commercial milk supply as dairies are required to divert milk from sick animals and all products are pasteurized, which inactivates bacteria and viruses, like influenza.

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