Bird Flu Infects Cows With Tiny Viral Dose

A recent study indicates that a mere 10 viral particles of the H5N1 bird flu are enough to infect dairy cows, a concerning finding given the virus's minuscule size. Since March 2024, the outbreak has spread to over 1,000 dairy herds spanning 19 states.

Scientists at Ohio State University discovered that H5N1 primarily targets dairy cows' mammary glands, producing high viral concentrations in milk. This differs from typical respiratory infections, presenting significant challenges for containment efforts.

Further research has explored various transmission pathways, but common routes like contaminated milking equipment, feeding calves infected milk, or airborne spread showed limited evidence of significant infection. Even direct exposure through the nose did not sicken cows.

Despite extensive testing, the exact cow-to-cow transmission method remains elusive, complicating the development of effective prevention strategies. Andrew Bowman, a professor at Ohio State University, emphasized the need to understand how the virus moves between cows, potentially through milking practices.

As of the article's publication, over 1,000 outbreaks of the B3.13 genotype have been confirmed in dairy herds across 17 states. A national milk testing strategy has been implemented to control the spread by halting the movement of herds producing contaminated milk.

The spillover of avian influenza into cattle, particularly affecting the mammary glands, represents a significant paradigm shift. A larger mystery persists regarding how the virus initially transfers from wild birds' digestive systems to cows' mammary glands.