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(huì)導(dǎo)致動(dòng)物癌癥的傳染病毒與慢性疲勞綜合癥聯(lián)系起來，這對(duì)于慢性疲勞綜合癥患者來說是一個(gè)重大發(fā)現(xiàn)，同時(shí)科學(xué)家們也擔(dān)憂其潛在的公共衛(wèi)生問題。

    預(yù)計(jì)全世界有1,700萬人患有慢性疲勞綜合癥，美國(guó)疾病控制與預(yù)防中心（Centers for Disease Control and Prevention）預(yù)計(jì)美國(guó)患此癥的人數(shù)為100萬-400萬。慢性疲勞綜合癥的特點(diǎn)是感覺衰弱疲勞并伴有長(zhǎng)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(yī)學(xué)界對(duì)于慢性疲勞綜合癥是否為一種確定的疾病尚存爭(zhēng)論。一項(xiàng)研究表明慢性疲勞綜合癥與一種強(qiáng)有力的病毒有關(guān)，這可能改變爭(zhēng)論的形勢(shì)。

    周四在《科學(xué)》（Science）雜志上發(fā)布的這項(xiàng)研究結(jié)果意義重大，遠(yuǎn)遠(yuǎn)超出了患慢性疲勞綜合癥的人群。研究結(jié)果發(fā)現(xiàn)，研究中作為對(duì)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(duì)此擔(dān)心不已。如果更大規(guī)模的研究證實(shí)了這些數(shù)據(jù)，那可能意味著美國(guó)最多有1,000萬人感染了這種病毒，全球感染人數(shù)可能達(dá)數(shù)億。這種病毒已經(jīng)與至少兩種疾病存在強(qiáng)烈關(guān)聯(lián)。

    這項(xiàng)研究由內(nèi)華達(dá)州里諾市的Whittemore Peterson神經(jīng)免疫疾病研究院、美國(guó)國(guó)立癌癥研究院（National Cancer Institute）以及克利夫蘭門診醫(yī)院（Cleveland Clinic）的研究人員進(jìn)行。這是首次在人類身上發(fā)現(xiàn)活體XMRV病毒。

    9月，猶他大學(xué)（University of Utah）和哥倫比亞大學(xué)醫(yī)學(xué)院（Columbia University Medical Center）的研究人員發(fā)現(xiàn)，他們所檢測(cè)的前列腺癌樣本有27%含有XMRV病毒。該研究還發(fā)現(xiàn)，良性前列腺樣本中有6%含有XMRV病毒。

    上述兩項(xiàng)研究都未能決定性地顯示XMRV導(dǎo)致了慢性疲勞綜合癥或前列腺癌。但美國(guó)國(guó)立癌癥研究院十分擔(dān)憂，于7月召開了一個(gè)非公開的討論會(huì)，討論XMRV感染對(duì)公共衛(wèi)生的影響。美國(guó)國(guó)立癌癥研究院艾滋病和腫瘤病毒研究中心負(fù)責(zé)人格萊斯（Stuart Le Grice）說，美國(guó)國(guó)立癌癥研究院對(duì)此采取了與艾滋病毒（HIV）發(fā)現(xiàn)之初一樣的反應(yīng)。格萊斯也是7月討論會(huì)的組織者之一。

    與艾滋病毒一樣，XMRV也是一種反轉(zhuǎn)錄病毒，這意味著一旦感染，病毒就永久留在感染者體內(nèi)；要么人體免疫系統(tǒng)對(duì)其進(jìn)行控制，要么需要進(jìn)行藥物治療。Whittemore Peterson研究院的米柯維茨（Judy Mikovits）說，這種病毒會(huì)導(dǎo)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(guān)病毒（Xenotropic murine leukemia virus-related virus）的XMRV病毒的復(fù)制速度似乎不像艾滋病毒那么快。科學(xué)家們也不知道XMRV通過何種途徑傳播，但患者的血液樣本發(fā)現(xiàn)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(fā)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(shù)據(jù)看，這種可能性很高。米柯維茨說，通過另外的檢測(cè)，科學(xué)家們確定研究中逾95%的患者受到活體病毒感染，或是產(chǎn)生了抗體，這表明他們的免疫系統(tǒng)向XMRV發(fā)起過攻擊，現(xiàn)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(huì)患艾滋病一樣，我認(rèn)為不可能找到?jīng)]有感染XMRV而罹患慢性疲勞綜合癥的病例。

    在7月的討論會(huì)上，米柯維茨還提交了初步數(shù)據(jù)，顯示101個(gè)研究對(duì)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(guān)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(guān)的可能性。美國(guó)國(guó)立癌癥研究院的格萊斯說，將進(jìn)行相關(guān)研究，確定XMRV是否與其他疾病相關(guān)。Whittemore Peterson研究院的米柯維茨說，他們還發(fā)現(xiàn)患孤獨(dú)癥、不典型多發(fā)性硬化和纖維肌痛的人體內(nèi)也有XMRV病毒。