Participants in the 119th Boston Marathon are at risk of developing hypothermia as they battle wind, rain and unseasonably cold temperatures on the way to the finish line, doctors say.“There are going to be a lot of cold, wet people,” said Dr. Pierre Rouzier, a family practice physician at UMass Amherst.Doctors volunteering at the race — a total of 120 across two tents — are equipped with blankets and Bair Huggers, which are devices that inflate with hot air and wrap around the patient.