Dairy Cattle Become Hosts for Avian Flu Transmission

A new study reveals evidence that avian influenza has spilled over from birds to dairy cattle across several U.S. states, resulting in mammal-to-mammal transmission between cows and from cows to cats and a raccoon.

This is one of the first times that we are seeing evidence of efficient and sustained mammalian-to-mammalian transmission of highly pathogenic avian influenza H5N1.”

Diego Diel, Associate Professor and Study Co-Corresponding Author, Virology, Department of Population Medicine and Diagnostic Sciences, Cornell University

Diel is also the Director of the Virology Laboratory at the Animal Health Diagnostic Center (AHDC) in the College of Veterinary Medicine.

Diel is the co-corresponding author of the study published in Nature.

Despite the fact that the data clearly indicates mammal-to-mammal transmission, whole genome sequencing of the virus did not find any mutations that would increase the transmissibility of H5N1 in humans. This is concerning because the virus may adapt in mammals, according to Diel.

Around 11 human cases have been reported in the United States to date, the first of which dates back to April 2022. All of the cases have mild symptoms, and four of them have been connected to cattle farms and seven to poultry farms, including an outbreak of four cases that has been reported in Colorado in recent weeks.

These recent patients fell ill with the same strain identified in the study as circulating in dairy cows, leading researchers to suspect that the virus likely originated from dairy farms within the same county.

Although the virus can infect and multiply in humans, the effectiveness of these infections is quite low.

The concern is that potential mutations could arise that could lead adaptation to mammals, spillover into humans and potential efficient transmission in humans in the future.”

Diego Diel, Associate Professor and Study Co-Corresponding Author, Virology, Department of Population Medicine and Diagnostic Sciences, Cornell University

Therefore, according to Diel, it is imperative to keep an eye out for any possible human infection as well as for the virus in afflicted animals. The US Department of Agriculture has funded programs for free H5N1 testing for farmers. Diel said that in order to stop the virus from spreading further, early testing, increased biosecurity, and quarantines in the event of positive results would be required.

Since the H5N1 virus was discovered for the first time in January 2022, thousands of wild birds and over 100 million domestic birds have perished in the United States. Scientists from the Texas A&M Veterinary Medical Diagnostic Laboratory and the Cornell AHDC were among the first to report finding the virus in dairy cattle herds.

The cows' symptoms, which included decreased appetite, altered fecal matter consistency, respiratory distress, and abnormal milk with noticeably less milk production, were probably caused by wild birds infecting them.

According to the study, the virus has a strong affinity for the mammary gland and can infect specific cells. It also exhibits high infectious viral loads in the milk of animals that are afflicted. Pasteurization kills the virus, ensuring a safe supply of milk.

When infected Texas cows were transferred to an Ohio farm with healthy cows, the researchers discovered instances of cow-to-cow transmission using whole genome sequencing of identified virus strains, modeling, and epidemiological data. According to sequencing data, the virus was also linked to cats, a raccoon, and wild birds that were discovered dead on afflicted farms.

It is highly likely that the raccoons and cats contracted illnesses from consuming raw milk from sick cows. The researchers believe that the infection of the wild birds may have been caused by environmental contamination or aerosols raised during milking or cleaning of the milking parlors, even though the exact cause of the infection is unknown.