Chronic fatigue syndrome (CFS) : Sudden debilitating fatigue of unknown cause.

慢性疲劳症候群：不明原因的突然虚弱疲劳。

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Doctors don't know what causes chronic fatigue syndrome, characterized by debilitating fatigue and chronic pain with symptoms that can wax and wane over time.

医生们不知道慢性疲劳综合症的致病原因。该病的特征是使人虚弱无力的疲倦、慢性疼痛，症状的轻重则可能随时间变化。

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CFS is characterized by debilitating fatigue and chronic pain, but there are no specific treatments, and the diagnosis is often made by ruling out other diseases.

慢性疲劳综合症的特点是感觉衰弱疲劳并伴有长期疼痛，但没有有效的治疗方法，其确诊通常也是通过排除其他疾病。

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The symptoms of CFS include debilitating fatigue, neurological problems, general pain, gastro-intestinal problems and a variety of flu-like symptoms.

BBC: News | Health | Immune system blamed for Chronic Fatigue Syndrome

The researchers reported they found the retrovirus XMRV in a majority of 101 patients with chronic fatigue syndrome, a debilitating condition that involves cognitive dysfunction and severe pain.

WSJ: Chronic-Fatigue Paper Called Into Question