MONROVIA, Liberia—President Ellen Johnson Sirleaf on Sunday said “the whole world has a stake” in preventing an unfolding catastrophe in Liberia, calling on nations to provide more medical experts and supplies to confront the exploding Ebola epidemic. But illustrating the difficulties of heeding that call, her own son, a physician, has stayed in the U.S., saying he can do more for his country there than at home.

“It is the duty of all of us as global citizens to send a message that we will not leave millions of West Africans to fend for themselves,” Mrs. Sirleaf said. In line with that message, the president in late August fired state officials who refused to come home from abroad to help Liberia battle Ebola.

At that time, however, her son, Dr. James Adama Sirleaf, was returning to his family in Georgia, after deciding to pull his medical training group out of his homeland because of mounting risks to doctors there.

He is hardly alone. Officials and physicians here say far more Liberian doctors are in the U.S. and other countries than in the country of their birth, and that their absence is complicating efforts to curb what has become a global health crisis.

Even before Ebola, there were only about 170 Liberian doctors in the country, and colleagues say many of them weren't actively practicing. At least four of them have since died of the virus. That shortage has prompted repeated pleas from the Liberian government for more foreign doctors to join the fight.