WASHINGTON (Reuters) - The United States and Europe face a new health threat from a mosquito-borne disease far more unpleasant than the West Nile virus. Chikungunya virus has spread beyond Africa since 2005, causing outbreaks and scores of fatalities in India and the French island of Reunion. It also has been detected in Italy, where it has begun to spread locally, as well as France. Unlike West Nile virus, where nine out of 10 people are going to be totally asymptomatic, or may have a mild headache or a stiff neck, if you get Chikungunya you're going to be sick....