What do you think, was it passed on by human or rat fleas?

你怎么看， 它是由人类还是老鼠跳蚤传播的？

Now, some scientists suggest that it was human fleas and lice that were the true culprits behind Europe’s version of the disease.

现在，一些科学家认为人类跳蚤和虱子才是欧洲版这种疾病的真正罪魁祸首。