当前的理论是，由于人类猎杀或食用了感染后的黑猩猩而传染上这种疾病的。
The leading theory is that it was picked up by people who hunted or ate infected chimpanzees.
之所以减少，主要是因为采取协调一致的公共卫生行动后，由传染病引起的视力损害减少了。
This decrease is principally the result of a reduction in visual impairment from infectious diseases through concerted public health action.
马丘·比丘在建成100年后就被废弃了，可能是因为天花的传染。
Machu Picchu was abandoned about 100 years after it was founded, possibly because of a smallpox epidemic.
应用推荐