Ten Viral Particles Trigger H5N1 Infection in Dairy Cattle

Since the virus first appeared in American dairy cattle in March 2024, it has surfaced in over 1,000 confirmed cases across 17 states. While current containment relies on testing milk to restrict herd movement, these findings highlight the extreme biological vulnerability of livestock. In controlled experiments, researchers introduced the virus directly into cow teats, triggering productive infections that resulted in high viral concentrations within the milk.

Despite this high infectivity, the transmission patterns remain largely mysterious. Tests attempting to spread the virus via milking equipment or by feeding calves contaminated milk yielded no infections. Furthermore, introducing the virus through the nasal passages failed to cause illness, suggesting the respiratory tract is not the primary entry point in cattle. Professor Andrew Bowman, the lead researcher, characterized the jump from waterfowl—where the virus replicates in the gut—to the cow’s mammary gland as a significant puzzle. While he cautioned that laboratory conditions may differ from the chaotic environment of a working farm, he emphasized that current protocols lack an effective strategy to prevent future spillover events or internal herd transmission.