From the Wall Street Journal health blog, 17 February 2011 (story by Amy Dockser Marcus).)
The debate over what XMRV may do to humans continues. But at least in a small group of monkeys, one thing is clear, according to a new study.
“The virus causes chronic, persistent infection,” says Robert Silverman of the Cleveland Clinic, a co-author of the paper, which was published online yesterday in the Journal of Virology. Moreover, the new research suggests that in these monkeys, at least, the virus can be difficult to detect in blood, even though it’s taken root in the body.
This is a tantalizing finding because it raises the prospect that someone could be infected with XMRV but show no clinical symptoms of disease until years, possibly decades, later.
The study involved five macaque monkeys who were infected intravenously with XMRV. Researchers were studying the monkeys for a variety of reasons. Abbott Labs — which helped fund the study and whose scientists were among the researchers — is one of a number of companies developing tests that could potentially be used to screen the blood supply for XMRV. Abbott scientists have used the XMRV-positive monkey blood in their test development process.
Researchers looking at what happens after XMRV infection in people also needed an animal model and monkeys are “about as close as we can get to what happens in humans,” says Eric Klein, a Cleveland Clinic prostate-cancer surgeon who was also involved in the study.
There has been concern about the possible risks XMRV poses to blood supply since a paper published in Science in 2009 reported finding the virus in 68% of chronic-fatigue syndrome patients as well as 4% of the healthy people studied. The discovery raised the possibility that people who show no apparent signs of ill health may be infected with the virus. The Science paper has also generated controversy over whether XMRV is tied to CFS or causes the disease.
The new monkey study illustrated some of the challenges that continue to perplex scientists. The animals showed signs of the virus in their blood right after being infected, but very soon afterward, those signs disappeared, making detection very tough. When monkeys were autopsied, however, organs including the spleen, lungs, and prostate contained XMRV-infected cells.
Klein, who specializes in prostate cancer, tells the Health Blog that the study showed that the gland is a “early target for XMRV,” which sets up a “genuine chronic infection” within a week. He adds that that this finding does not prove that XMRV causes prostate cancer, but it does raise important questions about the long-term consequences of XMRV infection.
Additional primate studies are underway that will explore other routes of infection, among other issues. “We know XMRV likes to live in the prostate,” Klein says. “Now we want to know what it is doing there.”