“It’s a huge challenge,” said Pierre-Olivier Ngadjole, a doctor with the Swiss humanitarian organization Medair, which runs the Munigi treatment center.At the hospital in South Kivu, Nathalie’s mother, Ms. Binja, said she was aware that she could be infected with mpox because of the close contact with her daughter. But she said, “I don’t want to leave her alone, I don’t want her to die.”