The departure of many Western development workers from Guinea, Liberia and Sierra Leone, the West African countries hit hardest by Ebola, has further weakened the region’s understaffed health systems at the very moment they are facing one of the most volatile public health crises ever. Liberia, population four million, has fewer than 250 doctors left in the entire country, according to the Liberia Medical and Dental Council. Seven doctors there have contracted Ebola, and two of them have died.

“The locals’ seeing this mass exodus of expatriates has contributed to the sense that there’s an apocalypse happening and they’re in it on their own,” said Raphael Frankfurter, executive director of the Wellbody Alliance, which provides clinical services in a diamond-mining district of Sierra Leone bordering Guinea, where the outbreak began.

Mr. Frankfurter, too, sent his four American volunteers home for fear they might fall ill. They left behind 160 Liberian staff members. “It’s certainly not in line with our values, because it’s just such a glaring inequality,” he said. But “it’s a very scary place to get sick right now.”