disease, illness, sickness 三者都可表示“疾病”，区别如下：
1. disease 表示“疾病”，通常指具体的“疾病”(可数)。
如：
Most diseases could be wiped out. 多数疾病是可以消灭的。
I caught the disease from you. 我这病是从你那传染来的。
It was a horrible disease. 这是一种可怕的疾病。
Arthritis is a chronic disease. 关节炎是一种慢性病。
Measles, mumps and influenza are common diseases. 麻疹、腮腺炎和流感是常见病。
注：有时指疾病的总称(不可数)，即通称的“疾病”。如：
Rats spread disease. 老鼠传染疾病。
Cleanliness helps prevent disease. 清洁有助于预防疾病。
Disease is usually caused by germs. 疾病多由病菌引起。
Many antibiotic drugs ore used to combat disease. 许多抗生素药品用来和疾病作斗争。
2. illness 和 sickness 常可通用，它们主要用于表示生病的时间或因病(disease)导致的不健康状态等。
如：
He can’t come because of illness. 他因病不能来。
He died after a long illness. 他死之前病了很久。
She is cheerful in spite of her illness. 她尽管有病，但还是快乐。
He was weak from a long illness. 由于长期生病他身体很虚弱。
Tell me a little about your illness. 给我谈谈你的病。
Chicken pox is a common childhood sickness. 水痘是儿童时期的常见病。
Do you know what his sickness is? 你知道他患什么病吗?
另外，sickness还可表示“呕吐”“恶心”。如：
He’s suffering from sickness and diarrhoea. 他上吐下泻。
He felt a wave of sickness come over him. 他感到一阵恶心。
3. 用于医学上表示各种病称时，通常用 disease。
如：
contagious diseases 传染病
English disease 气管炎
heart disease 心脏病
lung disease 肺病
a nervous disease 神经病
skin disease 皮肤病
注：有个别搭配也用 illness。如：
mental illness [sickness] 精神病
