The H5N1 bird flu virus has been around for decades, and the damage it wreaks on chickens and other poultry is well documented. But the recent discovery that the virus has jumped into dairy cattle — whose udders seem to be where the virus either infects or migrates to — has dumbfounded scientists and agricultural authorities.

Questions for which there are pretty clear answers when it comes to birds are suddenly unsettled science in cows. How are they getting infected? Are they transmitting the virus cow to cow, or are human actions — activities that are part of the day-to-day of farming — serving as an unrecognized amplifier of viral transmission? In the interface between infected cows and humans, how might people be at risk? Does consuming milk laced with live H5 virus pose a hazard?