LITTLE ROCK, Ark. – Nearly a third of all cocaine seized in the United States is laced with a dangerous veterinary medicine - a livestock de-worming drug that might enhance cocaine's effects but has been blamed in at least three deaths and scores of serious illnesses. The medication called levamisole has killed at least three people in the U.S. and Canada and sickened more than 100 others. It can be used in humans to treat colorectal cancer, but it severely weakens the body's immune system, leaving patients vulnerable to fatal infections. Scientific studies suggest levamisole might give cocaine a more...