A mysterious illness confined him to bed for months.

他因一种说不清、道不明的怪病卧床好几个月。

In 1959, a man residing in Africa died of a mysterious illness.

1959年，一个居住在非洲的男人死于一种诡秘的疾病。

That was when I first heard about an outbreak of mysterious illness that was happening in the Amazon rainforest of Peru.

那是我第一次听到秘鲁亚马逊雨林正在上演一场神秘疾病的大爆发。