This MEA summary is intended to be a factual and balanced account of the current situation. It follows the story of retroviral infection (ie XMRV and MLVs) in ME/CFS over the past year and tries to answer all the common questions that are being raised.
The summary is very cautious when it comes to drawing any firm conclusions about the role of retroviral infection in ME/CFS – as either a diagnostic marker, causative agent, or abnormality that requires treatment with antiviral medication.
We will continue to update this summary on the MEA website as new research information becomes available.
On Friday 9 October 2009, the front page of The Independent newspaper in the UK carried a major news item under the heading ‘Has science found the cause of ME?’ The story referred to research findings from America which suggested that a recently discovered retrovirus, known as XMRV (xenotropic murine leukaemia virus-related virus), could be playing a role in causing or maintaining ME/CFS.
The Independent story was soon followed up by the rest of the UK media. Most reports gave a reasonably balanced and accurate account of the research. However, some journalists incorrectly inferred that the cause of ME/CFS had now been discovered and that an effective antiviral treatment would soon be available. This created high expectations in the ME community.
THE SCIENCE PAPER
The American research was published in Science , along with a perspective  written by two highly respected retrovirologists: Dr John Coffin (Department of Molecular Microbiology, Tufts University, Boston, USA) and Dr Jonathan Stoye (National Institute for Medical Research, London). The most recent (and rather sceptical) review of the current situation comes from Professor Robin Weiss at University College London .
The key findings from the Science paper are summarised here:
* A research group from the Whittemore Peterson Institute (http://www.wpinstitute.org), in collaboration with the National Cancer Institute and the Cleveland Clinic, reported evidence of a human retrovirus known as XMRV in blood samples taken from people with ME/CFS.
* Using peripheral blood mononuclear cells, DNA (=viral genetic material) from the XMRV virus was found in 67% of patients (68/101) compared to 3.7% in healthy controls (8/218).
* The XMRV virus was shown to grow in cell culture in the laboratory.
* Further studies carried out by the group found that 95% of people with ME/CFS have antibodies to XMRV – indicating an immune response to a recent or past infection.
* Blood samples were collected from people with ME/CFS who met with both Fukuda research criteria and Canadian clinical criteria for CFS.
FOLLOW-UP STUDIES: THE IMPORTANCE OF REPLICATION AND VALIDATION
Since publication of these findings, there has been a great deal of interest from researchers in countries where ME/CFS is recognised and a number of research groups have attempted (or are still attempting) to confirm the positive findings. This is a vital part of the scientific evaluation process.
In relation to XMRV, a true replication study should involve exactly the same laboratory methods/assays and same type of patients that were used in the original study. A validation study is more flexible in that it allows other research groups to try and repeat the findings using what they feel are the most sensitive and accurate laboratory methods they have access to for testing for XMRV.
In the case of XMRV almost all of the first wave of research has involved validation studies. Firstly, because there is no international agreement about the most accurate and sensitive way of detecting XMRV in blood samples. Secondly, other research groups wanted to move quickly and the easiest way to do so was to use stored blood samples from people who had already been diagnosed with CFS according to Fukuda research criteria. Stored blood samples from people who meet both Fukuda and Canadian criteria for CFS are not readily available.
Results from five XMRV validation studies – three from Europe, one from the Centers for Disease Control (CDC) in America, and one from China – have now been published in scientific journals [4,5,6,7,8]. Results from a further study, carried out by Professor Brigette Huber, were presented at the Invest in ME conference in May 2010 (report available on MEA website and in the July 2010 issue of our quarterly magazine ME Essential).
Results from other studies, including some positive results from the UK and Italy, were also reported at an international XMRV conference in America in September but these studies have not yet been published.
None of these six research groups to report negative findings – which in the case of the UK included Professor John Gow, Dr Jonathan Kerr and Dr Jonathan Stoye and used patient samples from physicians including Dr Abhijit Chaudhuri and Professor Peter Behan – have been able to find XMRV in blood samples from ME/CFS patients, or in the healthy controls.
Although a number of valid criticisms have been made about these XMRV negative studies, in particular the one from the CDC in America, a number of distinguished virologists who work with retroviruses and XMRV have been involved – so the XMRV negative results have to be taken seriously.
A further study, from Dr Shyh-Ching Lo et al in America, involving 37 patients with Fukuda or Holmes defined CFS and 44 healthy controls, was published on 23 August 2010 . This is the first follow-up study to be published in a peer-reviewed journal to support (but not replicate) the original positive findings. Lo et al found segments of genetic material from what they term a genetically diverse group of MLV-related viruses. Along with XMRV, these viruses all belong to a closely related group of retroviruses. A detailed summary and statement on this study can be found on the MEA website (September 2010 news item).
RESEARCH IN PROGRESS OR AS YET UNREPORTED
A number of other XMRV replication and validation studies have been completed, or are in progress, and are not yet reported.
In America, a study has been set up to try and establish ‘gold standard’ testing methods that can be used consistently across XMRV studies. To pursue this objective, CDC, the Food and Drug Administration (FDA), the National Institutes of Health, and several non-federal laboratories are participating in an XMRV assay comparability study, which is being co-ordinated by a working group of the U.S. Department of Health and Human Services.
When completed, the results of this process should help researchers to more precisely replicate past studies and further study a potential link between XMRV and adverse health outcomes, including ME/CFS. This initiative should also help to clarify whether there is a true link between ME/CFS and retroviral infection.
In the UK, The MEA has been involved in helping to set up a small study that will retest people who have a positive XMRV blood test result from the USA in order to see if UK testing methods produce the same result. UK researchers are also investigating the possible role of XMRV in human disease.
XMRV AND OTHER CONDITIONS
XMRV has also been linked to a number of other conditions including autism, fibromyalgia and prostate cancer – where an American study reported finding the virus in men who have an aggressive form of prostate cancer. This was partly why the ME/CFS study was carried out.
However, other studies on XMRV in prostate cancer have queried any such a link and suggested that possible explanations could involve a geographically restricted incidence of XMRV.
Additional explanations for the differing results involve the type of sensitive laboratory testing for XMRV used in different studies. So the precise role of XMRV in prostate cancer remains uncertain – as it does in ME/CFS, autism and fibromyalgia.
PRESENCE OF XMRV and MLVs IN THE HEALTHY POPULATION
If these retroviruses (or viral particles) are also present in up to 7% of the normal healthy population here in the UK, as may be the case in America, and they do play a significant role in diseases such as ME/CFS and prostate cancer, there will be widespread and very serious implications for public health, blood donation etc. This could also include vaccination against the virus and treating people who are XMRV positive. These are complex decisions which can only be made in the light of further research studies.
The discovery of XMRV and MLVs in people with ME/CFS is clearly a very important finding that could help with both the diagnosis and management of ME/CFS. However, the repeated failure of other virologists to find XMRV in other groups of ME/CFS patients means that much of the scientific community remains uncertain or even sceptical about any such link.
The reason why some researchers are finding retroviruses in ME/CFS and others are not remain uncertain. Possible explanations include differences in patient selection, differences in the laboratory assays being used to detect XMRV and the presence of a laboratory artefact. Some retrovirologist believe that XMRV could even turn out to be what they call a ‘rumour virus’ in relation to disease causation – as happened when a new retrovirus named HRV5 was wrongly linked to rheumatoid arthritis a few years ago .
Given the current uncertainty, and conflicting research findings, it is therefore impossible to conclude that XMRV or MLVs are playing a significant role in either the cause, transmission, clinical assessment or management of ME/CFS.
What is now needed is international scientific agreement on which XMRV or MLV ‘gold standard’ test, or a battery of properly validated tests, should be consistently used in further research studies to see if there is indeed a correlation between ME/CFS and retroviral infection.
If a correlation cannot be accurately established there is little point in pushing on with further research into XMRV and MLVs in ME/CFS.
But, if a definite link can be established, the research community will then have to examine whether these viruses are disease/symptom causing, or are just a harmless passengers. In the latter case this could be as a result of immune dysfunction making people more susceptible to these type of infections – as may be the case with HHV-6.
If a retroviral infection is shown to be definitely present in ME/CFS, or just in a sub-group of ME/CFS patients, and it is a disease-causing virus (like HIV/AIDS) then clinical trials will have to take place into possible forms of treatment, including antiviral medication.
Researchers will also need to investigate:
* the prevalence of XMRV and MLVs in other chronic conditions, especially those such as multiple sclerosis and lymphoma where viral infections or immune dysfunction have been implicated as a causative factor and in other inflammatory conditions such as rheumatoid arthritis.
* whether XMRV and MLVs in healthy people act as a predisposing factor in the development of ME/CFS (possibly when another infective trigger appears) and/or prostate cancer – rather than being involved in the actual disease process.
* what other effect, if any, XMRV and MLVs have in healthy people who carry the infection over a period of time.
TESTING FOR XMRV and MLVs IN THE UK, EUROPE AND USA
Laboratory testing methods for XMRV include polymerase chain reaction (PCR) to detect the viral genome in tissue or peripheral blood mononuclear cells; RT-PCR and culture to detect viraemia in plasma; immunoflourescence to demonstrate viral antigen; and serology to detect a host response to infection. Each of these methods has potential shortcomings and may result in false positive and false negative reactions.
Until the research findings have been properly replicated, and we know for certain the most reliable way of testing for these viruses, there is no point in asking your doctor to be tested for XMRV or MLVs. This is because the NHS does not currently have the facilities to do so and XMRV testing procedures are only being used in a research capacity at present here in the UK.
But if it does eventually turn out that there is a consistent and strong retroviral association with ME/CFS then testing for XMRV and/or MLVs will have to be made available on the NHS.
We are not aware of any private pathology laboratories here in the UK that are able to test for XMRV or MLVs, or intend to offer such testing but tests are available in Belgium. It should be noted that concerns have been expressed about the reliability of some of the commercial tests that are now being promoted to the public.
So people do need to carefully consider the value of spending several hundred pounds on individual testing for the presence of XMRV or MLVs in the current situation. This because XMRV and/or MLVs have not yet been established as either diagnostic markers, disease causing viruses, or an infection that needs treating with antiviral medication. People also need to consider the possible implications, especially in relation to insurance, of having a positive result placed in their medical records.
Dr Vincent Lombardi, primary investigator and lead author of the Science
paper is Director of Operations for XMRV testing at Viral Immune Pathology Diagnostics (VIPDx) – a commercial laboratory in America. Website: http://www.vipdx.com
. This company is offering XMRV tests but the testing facility is not easily available to people living outside the US.
Contact details for anyone in Europe who does want to pursue XMRV testing:
TRANSMISSION OF XMRV and MLVs
We know that some people with ME/CFS are now very concerned about the possibility of transmission of XMRV and MLVs through what are termed body fluids (ie blood, breast milk, saliva, semen). However, until we know more about what these viruses do in the body, and how they are transmitted, it would be premature to start arriving at firm conclusions and recommending all kinds of restrictions to normal daily living.
And if these retroviruses were behaving as an ‘ME virus’ in the way that HIV, another retrovirus, causes and transmits HIV infection, often leading to AIDS, there would be a significant number of sexual partners of people with ME/CFS developing ME/CFS. But this is clearly not the case.
One simple way of obtaining some clues about viral transmission of XMRV and MLVs would be to test for their presence in healthy sexual partners and offspring of people who have the infection and comparing the findings to a control group of people that have no such link.
BLOOD DONATION AND XMRV
In relation to blood donation in the UK, current advice is that people with ME/CFS who have symptoms, or are receiving treatment, should not donate blood. Several overseas countries – Australia, Canada, New Zealand – have now followed the UK lead on blood donation and ME/CFS.
The MEA believed it would seem sensible in the short term, until we know more about transmission and pathogenicity of XMRV, to extend this restriction to people who have recovered from ME/CFS.
The MEA therefore wrote to Sir Liam Donaldson, former Chief Medical Officer at the Department of Health, in late 2009 regarding the possibility of XMRV being transmitted via human blood products and the implications that this has for blood donation.
A reply from the former CMO outlined the various expert bodies to whom attention had been drawn and advice was being sought. We wrote again to the new CM
O in 2010 asking for further clarification regarding people who have recovered from ME/CFS. We have now been informed that following this initiative it has been decided to extend the UK blood donation ban to people who have recovered from ME/CFS as from November 2010.
The CFIDS Association of America has been issued with guidance from the National Cancer Institute regarding blood donation in the US. The guidance can be read on the CFIDS website at: http://www.cfids.org
WHAT CAN WE LEARN ABOUT THE ROLE OF INFECTION FROM OUTBREAKS OF ME/CFS?
Unlike the retroviral infection HIV, ME/CFS is an illness that occurs both sporadically and in highly localised acute geographical outbreaks, often involving closed communities such as schools and hospitals, where there is no obvious evidence of bodily fluid transmission. This fact obviously questions the role of XMRV and MLVs as precipitating infections in the onset of the illness.
In the pivotal Royal Free Hospital outbreak of ME back in 1955, more than 7% of a previously healthy population of doctors and nurses contracted an unknown infection at roughly the same time (the hospital had to close due to lack of staff). This fact would question the role of retroviral infection as a key predisposing factor if it only occurs in 7% of the population.
POSSIBLE TREATMENT OF XMRV and MLVs: ANTIRETROVIRAL DRUGS AND VACCINES
Until we know more about the possible role of XMRV and MLVs in ME/CFS there is no point in asking your doctor for antiviral drug treatment. If it turns out that a retrovirus does play a role in causing or maintaining ME/CFS then antiviral drug treatment will need to be investigated. But this will first involve clinical trials to test possible drug treatments for both safety and efficacy – a process that normally takes a considerable amount of time and money.
However, as was pointed out in the issue July of our quarterly magazine ME Essential, antiretroviral drugs such as AZT can have serious side-effects, including damage to the muscle mitochondria (the powerhouse of the cell), that are very relevant to ME/CFS.
The 2007 NICE Guideline on ME/CFS specifically states that UK doctors should not use antiviral medication to treat ME/CFS. This dogmatic position is unlikely to change without clear evidence of benefit in good quality randomised clinical trials. The NICE guideline is likely to be reviewed in late 2010 or early 2011.
ROLE OF THE MEA RAMSAY RESEARCH FUND
The ME Association is keen to support good quality XMRV and MLV research here in the UK through any way we can help. We are in regular contact with a number of virologists and retrovirologists who are involved with retroviral infection here in the UK and are keen to pursue this work.
Funding from the Ramsay Research Fund (RRF) could be made available very quickly if we receive a good quality research proposal – preferably UK based. However, our contacts and discussions with UK researchers so far indicate that short-term funding is not an immediate problem and that all current research is being covered from existing budgets.
If volunteers are required for any XMRV or MLV research taking place in the UK we will place an announcement on the MEA website.
SELECTING PEOPLE FOR FURTHER RESEARCH STUDIES
There is clearly a need for international agreement and co-operation on the research criteria being used to select well-characterised ME/CFS patients for further research into XMRV and MLVs. Otherwise, we will end up with a collection of conflicting results on prevalence (= number of people currently infected) because different international research groups have been using different patient selection criteria.
In the present situation, many research groups are reluctant or unwilling to use Canadian criteria. This is because these are essentially clinical criteria and in the eyes of many researchers they have not been validated for use in research studies as stand alone criteria. There is also the problem in that most research groups do not having ready access to stored blood samples from ME/CFS patients or large numbers of fresh clinic patients that meet Canadian criteria.
So the best way forward may be for everyone to agree to use either Fukuda defined CFS – which would obviously help to define which sub-groups of patients are XMRV or MLV positive under this CFS umbrella – and, where possible, to use patients that meet both Fukuda CFS and Canadian clinical criteria. It is worth noting that a significant minority of people with Ramsay described ME will not meet Fukuda criteria for CFS – so they are likely to be excluded from research currently taking place.
We do not believe that it is sensible to extend the entry criteria into research studies by using the Oxford research criteria or the 2005 ’empirical’ definition of CFS for patient selection purposes as this will bring in an even more diverse group of patients who have chronic fatigue.
Provided there is careful selection of ME/CFS patients, healthy controls and disease controls, we should be able to draw some meaningful conclusions about which people who come under the wide clinical spectrum of ME/CFS presentations have XMRV or MLV and which do not.
Besides using stored blood samples, research needs to involve fresh clinical cases, as well as other disease groups (particularly inflammatory conditions with immune activation) and properly matched healthy controls.
The bottom line to this interesting research is that it currently raises more questions than answers and it seems likely that this uncertainly will continue till well into 2011. When we have accurate answers to at least some of the key questions about XMRV and MLVs, we can move forward, if necessary, with routine testing and clinical trials involving antiviral treatment.
KEY FACTS ABOUT RETROVIRUSES
* Retroviruses infect a wide range of animal species.
* Human retroviruses consist of HIV (causing AIDS) , HTLV-1 (causing T-cell leukaemias and lymphomas) and HTLV-2 (often asymptomatic and not yet clearly linked to any specific disease).
* They were discovered in the 1980s when it became possible to culture immune system T-cells in vitro.
* They infect CD4 bearing lymphocytes – a special type of immune system cell that is derived from the thymus gland.
* Endogenous retroviruses (ERVs) are also found in humans and usually cause no ill effects. Defective retroviruses which integrate into the host genome are passed down from generation to generation. Around 8% of the human genome is made up of endogenous retroviral sequences.
* Retroviruses are enveloped viruses, with an RNA genome. The name retrovirus is derived from the fact that the virus particle contains an RNA-dependent DNA polymerase – reverse transcriptase. This enzyme converts the RNA genome into DNA, which then integrates into the host chromosomal DNA. The reverse transcriptase enzyme is highly error prone and rapid genetic variation is therefore a feature of this group of viruses.
KEY FACTS ABOUT XMRV and MLV
* XMRV is an exogenous gammaretrovirus that was first described in 2006 in a group of men who had prostate cancer.
* It is the first gammetoretrovirus known to infect humans.
* The tissue tropism of XMRV is very different to the T cell tropism seen with HIV and HTLV.
* XMRV is closely related to a group of retroviruses that can infect mice.
* Xenotropic means the virus came from mice but mice are now immune to its effects.
* Humans probably acquired the virus from mice many years ago – precisely when the crossover occurred remains uncertain..
* This type of virus might be transmitted through body fluids such as blood, semen and breast milk. It is not thought to be transmitted through the air – like a flu virus. But the precise route of transmission remains unknown.
* Testing for evidence of the XMRV virus in blood is currently only available at a few specialised laboratories here in the UK.
* Demonstrating a link between a retrovirus and ME/CFS does not, by itself, immediately resolve the physical vs psychological debate. Research studies have demonstrated links between retroviruses and diseases as diverse as autoimmune disorders (which could be relevant to ME/CFS), immunodeficiency diseases, multiple sclerosis, tumours, anaemias and even psychiatric illnesses such as schizophrenia.
* Murine leukaemia viruses (MLVs) are retroviruses known to cause cancer in certain mice.
* MLVs are similar to XMRV but not the same.
1 Lombardi V et al. Detection of an infectious retrovirus, XMRV, in blood cells of patients with chronic fatigue syndrome. Science 2009, 326, 585-589.
2 Coffin JM and Stoye JP. A new virus for old diseases? Science 2009, 326, 530 – 531.
3 Weiss RA. A cautionary tale of virus and disease. BMC Biology 2010, 8, 124
4 Erlwein O et al. Failure to detect the novel retrovirus XMRV in chronic fatigue syndrome. PLoS ONE 2010, 5, e8519.
5 Groom HCT et al. Absence of XMRV in UK patients with chronic fatigue syndrome. Retrovirology 2010, 7:e10.
6 van Kuppeveld FJ et al. Prevalence of XMRV in patients with chronic fatigue syndrome in the Netherlands: retrospective analysis of samples from an established cohort. British Medical Journal 2010, c1018.
7 Switzer W et al. Absence of XMRV infection in patients with chronic fatigue syndrome and healthy controls in the United States. Retrovirology 2010, 7:57.
8 Hong P et al. Failure to detect xenotropic murine leukaemia virus-related virus in Chinese patients with chronic fatigue syndrome. Virology Journal 2010, 7:224.
9 Lo S-C et al. Detection of MLV-related virus gene sequences in blood of patients with chronic fatigue syndrome and healthy blood donors. Proceedings of the National Academy of Sciences 2010 September 7, 107, 15874 – 15879.
Dr Charles Shepherd
Hon Medical Adviser, The ME Association
5 October 2010