By Hillary Johnson, New York Times

Earlier this month, a study published in the journal Science answered a question that medical scientists had been asking since 2006, when they learned of a novel virus found in prostate tumors called xenotropic murine leukemia virus-related virus, or XMRV: Was it a human infection?

XMRV is a gammaretrovirus, one of a family of viruses long-studied in animals but not known to infect people. In animals, these retroviruses can cause horrendous neurological problems, immune deficiency, lymphoma and leukemia. The new study provided overwhelming evidence that XMRV is a human gammaretrovirus — the third human retrovirus (after H.I.V. and human lymphotropic viruses, which cause leukemia and lymphoma). Infection is permanent and, yes, it can spread from person to person (though it is not yet known how the virus is transmitted).

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