The first step was to find out exactly what the disease was doing. The team had set up operations in a village called Ler, which was several days' walk from Duar. Seaman and a handful of Nuer staff members began to scout on foot toward Duar. What they found was chilling. In some villages, cows wandered unattended; the entire human population had died. Many of the survivors looked like walking skeletons. Sick children carried starving babies after their parents had died on the road. The level of infection in blood tests from villagers in the region was so high that one lab questioned its own interpretation of the readings.

With the infection rate increasing, Seaman asked for an entomologist to pin down the vector, or carrier, of the disease and its habitat. MSF sent Canadian Judith Schorscher from her base in Paris. She spent six months using fans to suck insects into traps, where they could be dissected and analyzed.

It soon became apparent that the carrier was the female Phlebotomus orientalis sand fly, which passes the deadly protozoan to humans in an unusual manner (see box). The tiny insect, which cannot fly very high or far, inhabits the vast, red acacia forests, where it bites its victims in order to get protein-rich blood to develop its eggs. When female sand flies bit people driven by war or famine into the forests from areas where kala-azar was already endemic, the flies picked up the disease themselves, ready to be passed on.

Armed with the results of these early surveys, Seaman was determined to set up central operations in Duar. Hesselink, as MSF's country manager, disapproved. He claimed he would never be able to get a plane in to evacuate the staff if local trouble broke out between Sudan's warring factions. Seaman went over Hesselink's head, appealing to MSF's managers in Holland. Hesselink was furious, but he eventually admitted that setting up camp in Duar was sensible. Still he warned Seaman that if she ran into trouble, she might have to walk out on foot.

The flights into Duar were often spaced as much as six weeks apart, and cargo on the planes was so limited that although there were food shortages in the area, the staff frequently had to decide between food and medicine. "We saw patients' relatives losing weight because they were giving their food to sick family members," says Sjoukje De Wit, a Dutch nurse who became Seaman's sidekick. The doctors decided that they could eat less as long as the Nuer were starving.