MONDAY, Aug. 23 (HealthDay News) -- Another study has found
evidence that a mouse virus may play a role in chronic fatigue
syndrome, a poorly understood disorder that causes incapacitating
exhaustion and malaise.
Using blood samples collected in the mid-1990s from chronic
fatigue sufferers from the New England area, researchers found
evidence of gene sequences for murine leukemia virus (MLV)-related
virus in the blood of 32 of 37 patients, or 86.5 percent.
Evidence of the virus was detected in only three of 44 healthy
controls, or 6.8 percent of people who did not have chronic fatigue
syndrome, the researchers noted.
The team also did genetic testing on fresh blood samples from
eight of the chronic fatigue patients and found evidence of MLV in
seven of them.
The study, published in the Aug. 23-27 online edition of the
Proceedings of the National Academy of Sciences, was conducted by researchers from the U.S. Food and Drug Administration, Brigham and Women's Hospital in Boston, and the U.S. National Institutes of Health.
About one million people in the United States have chronic
fatigue syndrome, according to the Chronic Fatigue and Immune
Dysfunction Syndrome (CFIDS) Association of America. Symptoms
include debilitating exhaustion that lasts for months and is not
alleviated by sleep and often made worse by physical activity.
People with chronic fatigue can also experience joint aches and
muscle pain, headaches, enlarged lymph nodes and sore throat. At
the same time, many have to battle with the disbelief (from some
quarters) that CFS is a "real" disease.
The saga of MLV-related viruses and chronic fatigue syndrome
began last October, when a different team of researchers reported
in the journal
Science that they had found a mouse virus called xenotropic
murine leukemia virus-related virus, or XMRV, in the blood of 68 of
101 patients with chronic fatigue syndrome, but in only eight of
218 healthy patients.
Previously, the same team had reported that they found the virus
in some prostate cancer patients.
After decades of confusion about the illness, finally, it
seemed, researchers were honing in on a biological cause for the
mysterious condition, said Kim McCleary, president and CEO of the
CFIDS Association of America.
Yet four subsequent teams of researchers failed to find a
similar link, leaving patients even more confused. So, the new
findings are an important confirmation that an MLV-related virus
may indeed play a role, McCleary said.
"This study is certainly vindication for the disbelief that has been so pervasive over the past 20 years," McCleary said. "But as so often happens with science, every answer begs more questions."
Experts don't know if the presence of MLV-related virus gene
sequences reflect an underlying immune disorder, if the virus
alters the immune system and allows in other viruses, or if it's
the virus itself that is making people sick, McCleary said.
Also unexplained is why some healthy people have MLV-related
virus in their blood but don't fall ill, said Dr. Celia Witten,
director of the Office of Cellular, Tissue and Gene Therapies at
the U.S. Food and Drug Administration.
And the current findings differ from the previous research in
one important respect. While the findings reported in
Science identified xenotropic murine leukemia virus-related
virus (XMRV) in the blood of those with chronic fatigue, the
current study did not did find XMRV.
Instead, researchers found gene sequences for polytropic mouse
endogenous retroviruses, which are in the same family of
retroviruses but is not identical to XMRV, explained lead study
author Dr. Shyh-Ching Lo, director of the Tissue Safety Laboratory
Program at the U.S. Food and Drug Administration.
A retrovirus is a specific kind of virus that can integrate
itself into the host genome. Researchers don't know how it's
"Our study very much supports the earlier findings that MLV-related viruses are found in the chronic fatigue syndrome patients, although the virus sequence we identified is not the same as XMRV and is a much more heterogenous group," Lo said.
XMRV is a newly identified form of the MLV-related virus that
has been shown to infect human cells but not mouse cells, Witten
said, while polytropic MLV-related virus can infect both human
cells and mouse cells.
"Difference in sequences can cause difference in the virus' function and pathology," Witten said. "But exactly how pathogenic they are in people, how they cause infection or even whether they can all remains to be seen."
U.S. Centers for
Disease Control and Prevention has more on chronic fatigue.
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