In the Mali case, however, the girl was visibly sick, WHO said, and an initial investigation has identified 43 people, including 10 health workers, she came into close contact with who are being monitored for symptoms and held in isolation. The child was confirmed to have Ebola on Thursday.
"The child's symptomatic state during the bus journey is especially concerning, as it presented multiple opportunities for exposures — including high-risk exposures — involving many people," the agency said in a statement.
The girl first went to a clinic in Mali on Monday and she was initially treated for typhoid, which she tested positive for. When she did not improve, she was tested for Ebola.
Mali has long been considered highly vulnerable to Ebola's spread since it shares a border with the Ebola-hit countries of Guinea and Senegal, and staff from WHO and the U.S. Centers for Disease Control and Prevention were already there helping to prepare for a case. More WHO staff are being deployed.
The Ebola outbreak began in Guinea and has since spread to five other West African countries. The virus has also been imported to Spain and the United States. On Thursday, Craig Spencer, who had been working with Doctors Without Borders in Guinea and returned home to the U.S. about a week before, reported a fever and is now being treated at a New York hospital.
Some countries have banned travelers from the three main Ebola countries — Guinea, Liberia and Sierra Leone — and the U.S. started health screening of travelers arriving from there. But Doctors Without Borders said having its staffers quarantine themselves after leaving a country with Ebola is going too far if no symptoms are evident. A person infected with Ebola is not contagious until he or she starts showing symptoms.
"As long as a returned staff member does not experience any symptoms, normal life can proceed," Doctors Without Borders said in a statement sent to The Associated Press on Friday. "Self-quarantine is neither warranted nor recommended when a person is not displaying Ebola-like symptoms."
"Extremely strict procedures are in place for staff dispatched to Ebola affected countries before, during, and after their assignments," said Sophie Delaunay, the group's executive director, said in a statement. "Despite the strict protocols, risk cannot be completely eliminated. However, close post-assignment monitoring allows for early detection of cases and for swift isolation and medical management."
The group is investigating how Spencer became infected, it said.
Several spokespeople for the group refused to say where Spencer had been working in Guinea. Doctors Without Borders runs two treatment centers in Guinea: one in Gueckedou, in the southeast where the outbreak began, and the other in Conakry. It also runs a center near Gueckedou where patients are screened for Ebola and then sent for treatment if they have the disease.
Doctors Without Borders tells health workers who are returning home after a tour of duty that they must stay within four hours of a hospital with isolation facilities. It asks them to take their temperature twice a day and to be vigilant for symptoms, which include a fever.
The group said Spencer followed these procedures and immediately notified the New York office when he came down with a fever.
The group discourages staff returning from West Africa from going back to work before the incubation period is up, so they can recover from the grueling work in the field and also so they don't pick up an infection while at work whose symptoms may look like Ebola, causing unnecessary anxiety.