A recent study sheds light on why dairy cows infected with highly pathogenic avian influenza are transmitting the virus through their milk. These findings could help in developing strategies to mitigate the spread of the disease.
Sialic acid, a sugar molecule present on the surfaces of certain animal cells, acts as a receptor for influenza viruses. This receptor is crucial for the virus to attach, invade, and infect the host.
Prior to the recent outbreak of highly pathogenic avian influenza in dairy herds, little research had been conducted on sialic acid levels in the mammary glands of cattle. Scientists had not considered milk-producing organs as potential targets for influenza.
“In livestock, we typically focused on testing milk for bacteria rather than viruses,” stated Eric Burrough, a professor of veterinary diagnostic and production animal medicine.
A team of researchers from Iowa State University analyzed samples from the mammary glands of infected cows and found an abundance of sialic acid. This discovery could help understand how the virus attaches to hosts and aid in developing preventive measures.
“One hypothesis to prevent transmission could involve milking machines. Although their role in spreading the virus is unclear, it is a possibility,” said Todd Bell, a professor of veterinary pathology.
All commercially sold milk is pasteurized, which has been shown to deactivate viruses like influenza. However, the presence of the flu virus in the mammary glands of cows emphasizes the risks associated with consuming raw milk and raises concerns about the disposal of milk from infected cows.
“This research dismisses the idea of passive infection in mammary glands. Infected cows are producing a significant amount of virus, which poses a risk,” Burrough added.
While highly pathogenic avian influenza is not typically fatal for cows, it can be deadly for birds. The outbreak in the U.S. has affected over 97 million birds, leading to the euthanization of infected commercial poultry flocks.
The samples from infected dairy cattle examined by the ISU researchers showed receptors for flu strains originating from birds, humans, and pigs. The presence of these receptors increases the likelihood of dangerous mutations if a single cell is infected by both avian and mammalian viruses.
The study was published in the July issue of Emerging Infectious Diseases, the peer-reviewed journal of the Centers for Disease Control and Prevention. Most of the co-authors, 13 out of 14, were from Iowa State University, representing various departments in the College of Veterinary Medicine.
Rahul Nelli, a research assistant professor of veterinary diagnostic and production animal medicine, emphasized the importance of collaborative teamwork in addressing emerging public health threats.
Ongoing research may explore influenza receptors in other species and organs, with a specific focus on dairy cattle, according to Bell. As more data is gathered and herds are continuously screened, scientists’ understanding of how influenza affects cattle will advance.
“Surveillance will play a critical role in the future, not only during this event but in the years ahead,” Burrough concluded.
