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. So far, the risk to humans remains low, officials said, but scientists are wary that the virus could change to spread more easily among people. [time-brightcove not-tgx=”true”] The virus, known as Type A H5N1, has been detected in nearly three dozen dairy herds in eight states.