A recent study has found evidence that avian influenza, which originated in birds, has now spread to dairy cattle in multiple states in the U.S. This transmission has led to the transfer of the virus from mammal to mammal, specifically between cows and from cows to cats and a raccoon.
“This is among the first instances where we have observed efficient and sustained transmission of highly pathogenic avian influenza H5N1 between mammals,” stated Diego Diel, who is an associate professor of virology and heads the Virology Laboratory at the Animal Health Diagnostic Center in the College of Veterinary Medicine.
Diel is one of the lead authors of the research paper titled “Spillover of Highly Pathogenic Avian Influenza H5N1 Virus to Dairy Cattle,” which was published in Nature.
Although the entire genome sequencing of the virus did not show any mutations that would increase the transmissibility of H5N1 to humans, evidence of mammal-to-mammal transmission is evident. This raises concerns as the virus could potentially adapt in mammals, warned Diel.
Up to now, 11 human cases have been reported in the U.S., with the initial case dating back to April 2022. Most cases had mild symptoms and were connected to either cattle or poultry farms. Recent cases in Colorado showed a strain matching the one found in dairy cows, indicating a likely origin from dairy farms in the same area.
Although the virus can infect and replicate in humans, the transmission efficiency is currently low. The worry is that mutations could occur, enabling adaptation to mammals, human-to-human transmission, and potentially efficient spread among humans in the future, explained Diel.
Continuous monitoring of the virus in affected animals and suspected infected humans is vital, emphasized Diel. The U.S. Department of Agriculture has initiated programs for H5N1 testing, free of charge for producers. Diel stressed the importance of early testing, improved biosecurity measures, and isolation in case of positive results to prevent further virus transmission.
Infections from H5N1 were first identified in January 2022, resulting in significant losses among both domestic and wild birds in the U.S. Scientists from Cornell AHDC and Texas A&M Veterinary Medical Diagnostic Laboratory were among the first to detect the virus in dairy cattle herds. Infected cows likely contracted the virus from wild birds, displaying symptoms such as reduced appetite, fecal changes, respiratory issues, and abnormal milk production.
The study highlighted the virus’s affinity for the mammary gland and the high levels of infectious viral particles found in milk from infected animals.
Using whole genome sequencing, modeling, and epidemiological data, researchers identified instances of cow-to-cow transmission, as well as transmission to cats, a raccoon, and wild birds. Cats and the raccoon were presumably infected by consuming raw milk from infected cows. The cause of infection in wild birds remains uncertain, but researchers suspect environmental contamination or aerosols during milking operations as potential sources.
One of the co-corresponding authors, Kiril Dimitrov, who serves as the assistant agency director for microbiology and research and development at the Texas A&M Veterinary Medical Diagnostic Laboratory, collaborated on the study.
Co-first authors involved in the research include Leonardo Caserta, Elisha Frye, Salman Butt, and others from Cornell University. The study received funding from AHDC, the Ohio Animal Disease and Diagnostic Laboratory, Texas A&M Veterinary Medical Diagnostic Laboratory, and the USDA.
