Bird flu has been spreading among dairy cows in the US Getty Images/Cavan Images Public health experts still don’t know how a virus has been spreading for months among dairy cows in the US – though early evidence points to contaminated milking equipment. Since late March, have tested positive for H5N1, a bird flu virus that has killed and thousands of worldwide. Genetic analysis of samples from infected cattle suggests the outbreak began when cows on a Texas farm contracted.
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