Bird flu transmission occurs among cows via this mechanism.
The avian flu virus H5N1, initially found on an American dairy farm around springtime, has since spread quickly among cattle, impacting more herds as time passes. This transmission route of the virus has sparked interest, leading a research team to investigate. According to Martin Beer from the Friedrich-Loeffler-Institute (FLI) in Greifswald and Jürgen Richt from Kansas State University in Manhattan, the main method of transmission among cattle is through milk, primarily through milking equipment. These findings were published in the journal "Nature".
In their experiments, researchers infected calves and dairy cows with the H5N1 virus, specifically variant B3.13. This variant was first reported in March 2023 in dairy cows in the U.S. state of Texas, affecting 190 dairy operations in 13 U.S. states by early August.
Beer, Richt, and colleagues discovered that the B3.13 variant is a mix of an original European and North American avian flu virus. This pathogen may have jumped to cattle at the end of 2023 or the beginning of 2024 before spreading further.
No viral RNA found in blood and other tissues
Intriguingly, the researchers discovered varied outcomes depending on the method of infection. Cattle infected via the nose and mouth showed minimal symptoms, including nasal discharge and coughing. While some animals displayed these symptoms, they did not develop fever or experience other illness symptoms.
Upon adding additional calves twice later, none of them became infected. After seven days, only half of the originally infected calves exhibited small traces of viral genetic material within the upper respiratory tract tissue. Blood and other tissues, however, contained no viral RNA.
The story is different for cows infected through the udder, displaying compromised general health, ataxia, and lethargy within a day. Milk production dropped drastically, falling more than 90 percent for all affected cows. Milk became thick and mucus-like, quickly separating into liquid and solid components. This impacted both cows infected with variant B3.13 and test animals given a related European H5N1 variant.
Two cows, one from each group, grew so ill that they required euthanasia three days after infection. Milk samples from both groups revealed high viral loads. Autopsies revealed significant damage to milk glands, with dead cells appearing in high numbers. Genetic analyses uncovered a mutation that likely allows the virus to amplify within certain udder cells.
Significant barriers yet unsurmounted
Despite these findings, the FLI admits limitations to their study, citing the use of an early U.S. variant and testing a limited number of animals. "Fortunately, no human-to-human transmission has been reported so far," the study authors write. "This supports the assumption that these strains have not yet overcome critical barriers to enable human-to-human transmission." However, the U.S. dairy industry team emphasizes the importance of heightened vigilance if unusual milk characteristics are detected. Unusual cases could potentially be linked to avian flu infection and require further investigation. An effective surveillance strategy is vital for managing outbreaks among cattle.
In light of these findings, global health organizations in the United States of America are closely monitoring the spread of the B3.13 variant, given its potential impact on the dairy industry within the country. The United States of America, being a major exporter of dairy products, needs to mitigate any potential threats to ensure food safety and maintain global market stability.
