By Fran Kritz A tsetse fly — their bite can spread the parasite that causes sleeping sickness. Patrick Robert/Corbis/Sygma/via Getty Images hide caption Sleeping sickness is a notorious disease — immortalized in Joseph Conrad's Heart of Darkness. A single bite from a tsetse fly carrying the parasite is all it takes to infect someone. Without treatment one form of the illness can progress from mild symptoms to death in a matter of weeks. Now, a new drug holds the promise of helping the World Health Organization meet its goal of eliminating the disease by 2030. A committee of the European Medicines Agency has given an important green light to the first single-dose treatment — a medication called acoziborole, which could be in use by early next year.…