BAMAKO, Mali — Many people in Mali are at high risk of catching Ebola because the toddler who brought the disease to the country was bleeding from her nose as she traveled on a bus from Guinea, the World Health Organization warned Friday. The U.N. agency is treating the situation as an emergency because many people may have had “high-risk exposures” to the 2-year-old girl during her journey through several towns in Mali, including two hours in the capital, Bamako. The toddler died in an isolation tent at a hospital in the western city of Kayes on Friday, according to a nurse.