TB is a serious illness, but it can be cured.

肺结核虽然是一种严重的疾病，但可治愈。

Laziness is a serious illness and one must cure it immediately; yes, even from early childhood.

懒惰是种可怕的疾病，必须马上治；应该在小的时候就治好。

A very high temperature often denotes a serious illness.

高烧常常说明病得很重。

I am sorry to hear of your serious illness.

得悉病重，甚感难过。

During his serious illness he lost over ten jin.

他害了一场大病，体重掉了十多斤。