Dr. Liu said agencies like the World Health Organization, the Centers for Disease Control and Prevention and other aid groups should become more involved in prevention and surveillance, including tracing the contacts of people who are sick.

“We need more people in the field,” she said.

The virus has bred a larger medical crisis, Dr. Liu said. In Liberia’s capital, Monrovia, the health system collapsed as workers and patients fled hospitals out of fear of Ebola, allowing diseases like malaria, pneumonia and diarrhea to kill children who would otherwise have been saved. She said she learned from her staff about six pregnant women who lost babies because they could not find an open maternity ward.