请教一道题的中文意思

alex

Although schistosomiasis is not often fatal, [U]it is so deliberating that it has become an economic[/U] drain on many developing countries.

这道题的答案就是A，可是看了几遍都觉得有逻辑问题，不知大家如何理解题意？

alex

啊！这里有个拼写错误，应该是‘STRAIN’不是‘DRAIN’。