Scientists say they have discovered a promising treatment for sleeping sickness, a killer disease that infects(感染) about 60,000 people in Africa a year. British and Canadian experts say drugs could attack the parasite（寄生虫） causing the illness needs to survive. They say the drug could be ready for human medical test in about 18 months. The disease, spread by the bite of a fly, is caused by a parasite attacking the central nervous system. It has similar symptoms（症状） to malaria（疟疾）, making it difficult to diagnose. Left untreated, it moves to the brain, resulting i