By Matt McGrath, BBC World Service

媒体英语会带大家一起学习 BBC 撰稿人在报道世界大事时常用到的单词和短语。

Background: 科学家首次揭示了欧洲黑死病鼠疫病源的遗传密码。

黑死病或人们常说的欧洲大瘟疫，曾于14世纪夺走了成千上万欧洲人的生命。

Humans have rarely encountered an enemy as devastating as the bacterium Yersinia pestis. Between 1347 and 1351 it sparked the Black Death, an infection carried by fleas that spread rapidly across Europe, killing around 50 million people.

Now scientists have uncovered some of the genetic secrets of the plague, thanks to DNA fragments drilled from the teeth of victims buried in a graveyard in East London.

The researchers say that all current strains circulating in the world are directly related to the medieval bacterium. And while the infection still kills 2,000 people globally every year, it's much less of a threat because our immune systems have adapted to it.

The scientists say the techniques used to rebuild the genome of the Black Death could now be used to reconstruct other ancient pathogens.