More cows are being tested and tracked for bird flu. Here's what that means

U.S. health and agriculture officials are ramping up testing and tracking of bird flu in dairy cows in an urgent effort to understand and stop the growing outbreak. Officials say the risk to humans remains low. Scientists fear that the virus that's been detected in cattle in several states could change to spread more easily among people. Experts say genetic details show that the virus may have been spreading in cows since late last year. One scientist likens the situation to a tornado watch: there are some of ingredients for a threat but it's not certain to happen.