Enlarge (credit: Getty | Edwin Remsberg)

The highly pathogenic avian influenza H5N1 virus that spilled from wild birds into US dairy cows late last year may have recently seeped from a dairy farm in Colorado to a nearby poultry farm, where it then infected five workers tasked with culling the infected chickens

In a press briefing Tuesday, federal officials reported that four of the avian influenza cases have been confirmed by the Centers for Disease Control and Prevention, while the fifth remains a presumptive positive awaiting CDC confirmation.

All five people have shown mild illnesses, though they experienced variable symptoms. Some of the cases involved conjunctivitis, as was seen in other human cases linked to the H5N1 outbreak in dairy cows. Others in the cluster of five had respiratory and typical flu-like symptoms, including fever, chills, sore throat, runny nose, and cough. None of the five cases required hospitalization.

Enlarge / Fresh raw milk being poured into a container on a dairy farm on July 29, 2023, in De Lutte, Netherlands. (credit: Getty | Pierre Crom)

Despite the delusions of the raw milk crowd, drinking unpasteurized milk brimming with infectious avian H5N1 influenza virus is a very bad idea, according to freshly squeezed data published Friday in the New England Journal of Medicine.

Researchers at the University of Wisconsin-Madison squirted raw H5N1-containing milk from infected cows into the throats of anesthetized laboratory mice, finding that the virus caused systemic infections after the mice were observed swallowing the dose. The illnesses began quickly, with symptoms of lethargy and ruffled fur starting on day 1. On day 4, the animals were euthanized to prevent extended suffering. Subsequent analysis found that the mice had high levels of H5N1 bird flu virus in their respiratory tracts, as well their hearts, kidneys, spleens, livers, mammary glands, and brains.

"Collectively, our data indicate that HPAI [Highly Pathogenic Avian Influenza] A(H5N1) virus in untreated milk can infect susceptible animals that consume it," the researchers concluded. The researchers also found that raw milk containing H5N1 can remain infectious for weeks when stored at refrigerator temperatures.