英语语法分析

On the other hand, rainfall increased in the interior of western Africa, and the northern limit of the tsetse fly, an insect fatal to cattle, moved south.

另一方面，西非内陆的降雨量增加，采采蝇活动区域的北部边界向南移动——一种对牛致命的昆虫。

Tsetse flies are found just in sub-Saharan Africa though only certain species transmit the disease.

采采蝇仅在南撒哈拉非洲存在，但只有某些种类的采采蝇会传播该病。

The disease, transmitted mainly by tsetse flies, is prevalent in 37 countries among the poorest of the world.

这一疾病主要是通过采采蝇传播，在全世界最贫困的37个国家中流行。