Virology Blog: XMRV infection of Rhesus macaques

Cort

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Here was my take on it

Dr. Raccaniello Takes A Look at the Recent Macaque Study Published - among other things he noted the wide variety of tissues effected including spleen, lymph nodes, the lining of the gastrointestinal tract, prostate, testis, cervix, vagina, and pancreas, but not in others including brain, heart, kidney, and bladder and that XMRV showed up in the prostate early. The concentration of XMRV in the reproductive tissues (testis, cervix, vagina) suggests it may be transmitted sexually. He noted that the virus levels plummet after the acute infection but that immunocompromised individuals may show a different pattern (increased levels of virus?). He also noted that the authors stated that if XMRV causes CFS or prostate cancer the link would be a 'temporally distant one" which just seems to suggest that it looks like it would take a substantial amount of time to do its mischief. He stated that in interpreting the results of animal studies, we must keep in mind the adage, ‘Mice lie, monkeys exaggerate‘. We also learned that each monkey costs $50,000!

Question session - the questions were the most interesting part of the blog. In response to a question about looking for XMRV in human tissues he felt that the study should prompt research into that: "this work should stimulate research into understanding where XMRV can be found in humans". One interesting question notes that the investigators were able to 're-activate the virus by stimulating the virus and asks why not do that in humans? Or why not simply have people with CFS exercise and see what happens?

Look in the organs - Dr. Raccaniello clearly felt the study explained why XMRV might be so difficult to detect in humans and thought researchers should start looking in the organs. "You are right, from the results of this study it is clear that we should be looking for XMRV in other organs, rather than blood. As the authors write, if XMRV is involved in CFS and PC, the infection probably occurred some time before disease. And the findings do suggest why the virus is difficult to detect in the blood. Even proviral DNA was not detected, although in at least one monkey it was still present.

No need to kill cells to cause damage - to a question of how XMRV could cause damage if it's not killing cells Dr. Racaniello replied - actually there are a number of ways: "Many viruses are noncytopathic in cell culture, yet cause disease in humans. The tissue/organ damage is believed to be a consequence of immunopathology - the immune response damages cells and tissues. There is experimental support for this mechanism of pathogenesis for a number of human viral diseases. See http://www.virology.ws/2009/01.../.
 

Jemal

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I thought it was a very hopeful article. XMRV seems more like a "real" virus again, not a rumor virus or contamination.
I think it's highly likely that much of the damage is caused by our immune systems and not the virus itself. The question is: does XMRV cause misschief of its own as well? If not, we need ways to put the immune system down. Or we need to eliminate the virus, but that may be even harder.