Researchers have linked an infectious virus known to cause cancer in animals to chronic-fatigue syndrome, a major discovery for sufferers of the condition and one that concerned scientists for its potential public-health implications.

    An estimated 17 million people world-wide suffer from chronic-fatigue syndrome, and the Centers for Disease Control and Prevention puts the U.S. figure at between one million and four million. 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. Thus there is disagreement in the medical community as to whether CFS is a distinct disease. A study showing a strong viral association with CFS could change that equation.

    The significance of the finding, published Thursday in Science, extends far beyond the community of people living with CFS. Researchers are just as concerned about the finding that nearly 4% of healthy people used as controls in the study were also infected with the virus, called XMRV. If larger studies confirm these numbers, it could mean that as many as 10 million people in the U.S. and hundreds of millions of people around the world are infected with a virus that is already strongly associated with at least two diseases.

    The study, the first to find live XMRV in humans, was done by researchers at the Whittemore Peterson Institute for Neuro-Immune Disease in Reno, Nev., the National Cancer Institute and the Cleveland Clinic.

    In September, researchers at the University of Utah and Columbia University Medical Center found XMRV in 27% of the prostate-cancer samples they examined. That study also showed that 6% of the benign prostate samples had XMRV.

    Neither study conclusively shows that XMRV causes chronic-fatigue syndrome or prostate cancer. But the National Cancer Institute was sufficiently concerned to convene a closed-door workshop in July to discuss the public-health implications of XMRV infection. 'NCI is responding like it did in the early days of HIV,' says Stuart Le Grice, head of the Center of Excellence in HIV/AIDS and cancer virology at NCI and one of the organizers of the July workshop.

    Like HIV, XMRV is a retrovirus, meaning once someone is infected, the virus permanently remains in the body; either a person's immune system keeps it under control or drugs are needed to treat it. The virus creates an underlying immune deficiency, which might make people vulnerable to a range of diseases, said Judy Mikovits of the Whittemore Peterson Institute and one of the lead authors on the paper.

    So far, XMRV, known fully as xenotropic murine leukemia virus-related virus, doesn't appear to replicate as quickly as HIV does. Scientists also don't know how XMRV is transmitted, but the infection was found in patients' blood samples, raising the possibility that it could be transmitted through blood or bodily fluids.

    While Thursday's paper doesn't demonstrate conclusively that XMRV is a cause of CFS, additional unpublished data make it a very strong possibility. Dr. Mikovits said that using additional tests, the scientists determined that more than 95% of the patients in the study are either infected with live virus or are making antibodies that show their immune systems mounted an attack against XMRV and now had the virus under control. 'Just like you cannot have AIDS without HIV, I believe you won't be able to find a case of chronic-fatigue syndrome without XMRV,' Dr. Mikovits said.

    At the July workshop, Dr. Mikovits also presented preliminary data showing that 20 patients of the 101 in the study have lymphoma, a rare form of cancer. The link between XMRV and lymphoma is still being investigated, but it raised the possibility that XMRV may be associated with other cancers in addition to prostate cancer. NCI's Dr. Le Grice said studies will be launched to determine whether XMRV is associated with other diseases. At the Whittemore Peterson Institute, Dr. Mikovits said they also found XMRV in people with autism, atypical multiple sclerosis and fibromyalgia.

    研究人員將一種已知會導致動物癌癥的傳染病毒與慢性疲勞綜合癥聯系起來，這對于慢性疲勞綜合癥患者來說是一個重大發現，同時科學家們也擔憂其潛在的公共衛生問題。

    預計全世界有1,700萬人患有慢性疲勞綜合癥，美國疾病控制與預防中心（Centers for Disease Control and Prevention）預計美國患此癥的人數為100萬-400萬。慢性疲勞綜合癥的特點是感覺衰弱疲勞并伴有長期疼痛，但沒有有效的治療方法，其確診通常也是通過排除其他疾病。因此醫學界對于慢性疲勞綜合癥是否為一種確定的疾病尚存爭論。一項研究表明慢性疲勞綜合癥與一種強有力的病毒有關，這可能改變爭論的形勢。

    周四在《科學》（Science）雜志上發布的這項研究結果意義重大，遠遠超出了患慢性疲勞綜合癥的人群。研究結果發現，研究中作為對照組的健康人中有近4%也感染了這種名為XMRV的病毒，研究人員對此擔心不已。如果更大規模的研究證實了這些數據，那可能意味著美國最多有1,000萬人感染了這種病毒，全球感染人數可能達數億。這種病毒已經與至少兩種疾病存在強烈關聯。

    這項研究由內華達州里諾市的Whittemore Peterson神經免疫疾病研究院、美國國立癌癥研究院（National Cancer Institute）以及克利夫蘭門診醫院（Cleveland Clinic）的研究人員進行。這是首次在人類身上發現活體XMRV病毒。

    9月，猶他大學（University of Utah）和哥倫比亞大學醫學院（Columbia University Medical Center）的研究人員發現，他們所檢測的前列腺癌樣本有27%含有XMRV病毒。該研究還發現，良性前列腺樣本中有6%含有XMRV病毒。

    上述兩項研究都未能決定性地顯示XMRV導致了慢性疲勞綜合癥或前列腺癌。但美國國立癌癥研究院十分擔憂，于7月召開了一個非公開的討論會，討論XMRV感染對公共衛生的影響。美國國立癌癥研究院艾滋病和腫瘤病毒研究中心負責人格萊斯（Stuart Le Grice）說，美國國立癌癥研究院對此采取了與艾滋病毒（HIV）發現之初一樣的反應。格萊斯也是7月討論會的組織者之一。

    與艾滋病毒一樣，XMRV也是一種反轉錄病毒，這意味著一旦感染，病毒就永久留在感染者體內；要么人體免疫系統對其進行控制，要么需要進行藥物治療。Whittemore Peterson研究院的米柯維茨（Judy Mikovits）說，這種病毒會導致潛在的免疫缺乏，這可能令人容易罹患多種疾病。米柯維茨是該論文的主要作者之一。

    迄今為止，全稱異嗜性小鼠白血病病毒相關病毒（Xenotropic murine leukemia virus-related virus）的XMRV病毒的復制速度似乎不像艾滋病毒那么快。科學家們也不知道XMRV通過何種途徑傳播，但患者的血液樣本發現感染，令這種病毒通過血液或體液傳染的可能性增加。

    雖然周四發表的論文并未決定性地顯示出XMRV病毒是慢性疲勞綜合癥的起因，但從未公布的其他數據看，這種可能性很高。米柯維茨說，通過另外的檢測，科學家們確定研究中逾95%的患者受到活體病毒感染，或是產生了抗體，這表明他們的免疫系統向XMRV發起過攻擊，現在已控制住這種病毒。米柯維茨說，就跟沒感染艾滋病毒就不會患艾滋病一樣，我認為不可能找到沒有感染XMRV而罹患慢性疲勞綜合癥的病例。

    在7月的討論會上，米柯維茨還提交了初步數據，顯示101個研究對象中有20名患者有淋巴瘤，這是一種罕見的腫瘤。XMRV和淋巴瘤之間的關系仍在研究，但這增加了XMRV與前列腺癌之外的其他癌癥相關的可能性。美國國立癌癥研究院的格萊斯說，將進行相關研究，確定XMRV是否與其他疾病相關。Whittemore Peterson研究院的米柯維茨說，他們還發現患孤獨癥、不典型多發性硬化和纖維肌痛的人體內也有XMRV病毒。