Humans and horses may be falling victim to the same tick-borne ailment, until now believed to have been two separate diseases that mimic Lyme disease. The twin diseases -- human granulocytic ehrlichiosis (HGE) and equine granulocytic ehrlichiosis (EGE) -- are a mouthful to pronounce and equally tricky to diagnose. Symptoms in humans include a fever, headache, shaking chills and nausea. "Humans and horses appear to be getting the same disease, but they aren't catching it from each other," says Dr. John Madigan, a professor of equine medicine at UC Davis and lead author of a study that will appear in the October issue of the Journal of Infectious Diseases. After comparing the genetic makeup of the bacterium that causes the human disease with that found in horses, Madigan and colleagues found they were 99.8 percent the same. He hopes this discovery will lead to quicker and more accurate diagnosis and treatment in humans.