>>African culture itself—still strongly infused with superstition—is playing no small part?
I have little knowledge of Liberian culture, but my guess would be that this is very much a second-order effect. There was a comment on NPR this morning that one floor of the Brigham hospital in Boston has more doctors than all of Liberia. This is a very tough disease to manage absent skilled nursing and effective isolation wards.
I hate to say it, but I could imagine infected people just being left to die without medical help at all.