Research Confirms Bird Flu Can Spread Among Mammals

A new study has provided evidence that avian influenza, a type of flu virus originating from birds, has spilled over to dairy cattle across several U.S. states and led to mammal-to-mammal transmission between cows and from cows to cats and a raccoon. This alarming finding was released by Cornell University. 
 
Diego Diel, Associate Professor of Virology in the Department of Population Medicine and Diagnostic Sciences at Cornell University’s College of Veterinary Medicine, commented: "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." 
 
Diel co-authored the research paper entitled "Spillover of Highly Pathogenic Avian Influenza H5N1 Virus to Dairy Cattle," published on July 25th in Nature journal. The work involved whole genome sequencing, which revealed no mutations leading to enhanced human transmissibility but did confirm mammal-to-mammal spread. 
 
Despite this, there have been 11 recorded human cases within the United States as early as April 2022; four were linked to cattle farms, while seven were connected to poultry farms, including an outbreak reported recently in Colorado. Experts believe these humans contracted the virus from infected dairy cows residing within their vicinity. 
 
While this strain can infect humans, it does not transmit efficiently among them yet. However, Diel notes potential future changes: “The concern is that potential mutations could arise that could lead to adaptation to mammals, spillover into humans, and potential efficient transmission in humans.” 
 
Thus far, since January 2022, when infections were first detected among domesticated birds, more than 100 million deaths have occurred, along with thousands of wild bird casualties too. Scientists at Cornell AHDC's and Texas A&M Veterinary Medical Diagnostic Laboratory became aware that dairy herds had become infected, likely due to wild bird contact, causing reduced appetite symptoms, respiratory distress issues, and a notable decrease in milk production. 
 
The research reveals a high tropism of the virus for the mammary gland and significant viral loads in milk from affected animals. Thankfully, pasteurization kills this virus, ensuring a safe milk supply. 
 
Through whole genome sequencing of characterized viral strains, modeling, and epidemiological information, researchers determined cases of cow-to-caw transmission when infected Texas cows were moved to an Ohio farm with healthy cows. Sequencing also revealed that the flu was transmitted to cats, a raccoon, and wild birds found dead on affected farms. Cats and raccoons likely became ill after consuming raw milk from infected cows, while wild birds may have been exposed via environmental contamination or aerosols during milking parlor cleaning. 
 
Kiril Dimitrov from the Texas A&M Veterinary Medical Diagnostic Laboratory is another co-corresponding author, along with several other contributors, including Leonardo Caserta, Elisha Frye, and Salman Butt, among others, all belonging to Cornell University’s Department of Population Medicine and Diagnostic Sciences team. 
 
This study received funding support from AHDC, Ohio Animal Disease & Diagnostic Laboratory, Texas A&M Veterinary Medical Diagnostic Laboratory, and the USDA, emphasizing the importance ongoing vigilance testing funded by the U.S. Department of Agriculture at no cost producers essential early detection alongside enhanced biosecurity quarantine measures if positive results are detected, helping limit further spread of potential dangerous disease outbreaks across the USA farming industry, potentially affecting the human population too.