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Seeking New Blood-Supply Test

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Scientists are racing to develop tests for a retrovirus called XMRV, which could be used to determine if the blood supply is tainted and to assess how many people may be infected.

The impetus behind the drive is a paper published in the journal Science last year that reported a link between XMRV and chronic fatigue syndrome. Public health officials were alarmed that close to 4% of healthy people used as controls in the study were infected with XMRV. That could mean as many as 10 million Americans are infected.

XMRV has gotten a lot of attention because, like HIV, it is a retrovirus. This means the virus cannot be eradicated from the body, only controlled. There is some preliminary evidence that XMRV may be transmitted sexually or through transfusions. While the retrovirus has been linked to certain diseases, scientists don't yet know if it actually causes any disease.

The virus doesn't appear to replicate as frequently as HIV, making it challenging to detect. How labs handle blood samples before they test for XMRV may have an impact on results, some researchers believe. Some labs haven't been able to find it in people with chronic fatigue syndrome or prostate cancer, which have both been linked to the retrovirus. There has also been debate over the criteria used to define patients with chronic fatigue syndrome. These issues have made it challenging to come to a consensus on how many people are actually infected and whether or not XMRV poses a health risk.

Tests are in the works at a number of labs, including the Centers for Disease Control and Prevention and the National Cancer Institute as well as Abbott Diagnostics, a division of Abbott Laboratories, and Gen-Probe Inc. Roche Diagnostics says it expects to have a test for research purposes ready in months. Michael Busch, director of the Blood Systems Research Institute in San Francisco and a member of a federally funded blood-working group studying the potential impact on the blood supply, says the group pushed for companies to get involved early on in developing XMRV tests because they have technology that allows them to screen thousands of samples quickly. This kind of capacity "is critical to support our research studies and resolve the questions about XMRV," Dr. Busch says.

Various labs have their own tests but not everyone has been able to find XMRV in patients. If it turns out that XMRV is associated with diseases, there will be a need to screen large numbers of people and fast, reliable methods to test for it.

A key challenge is that these are still early days in understanding XMRV. Researchers usually calibrate tests against clinical samples that everyone agrees are positive and negative for the virus. A successful test would correctly determine which samples are infected. In the case of XMRV, there isn't yet scientific consensus. Some labs have said they cannot find XMRV in blood samples from patients that other labs have deemed positive.
 
 

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