目前一项首要重点是防止病毒在该国人口密集的城市或城郊地区立足。
A top priority at present is to prevent the virus from establishing a foothold in densely populated urban or peri-urban parts of the country.
这里的复杂程度指的是把人们组织成大型的、多样化的群体和人口密集的社区。
The level of complexity here refers to the organization of people into large, diverse groups, and densely populated communities.
如果这种病毒能够通过空气传播，或者如果一名感染者在不知情的情况下进入了人口密集的地区，那么埃博拉可能已经成为一种全球流行病。
If the virus had been capable of spreading through the air, or if one infected person had unknowingly entered a large population center, Ebola might have become a worldwide epidemic.
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