“We’re really hoping this will blow the lid off,” said Mary Schweitzer, a historian who has written and spoken about having the illness. “Patients are hopeful that now the disease itself might be treated seriously, that they’ll be treated seriously, and that there might be some solution.”

The senior author of the new paper, Dr. Harvey J. Alter, an infectious-disease expert at the National Institutes of Health, said he was well aware of the intense interest in his findings but had been unable to respond publicly.

“I was sympathetic to the desire of people to know, and it was difficult because we didn’t feel we could communicate with the patient community directly until the paper was published,” he said.

Retroviruses, including H.I.V., store their genetic code as RNA, convert it to DNA and integrate themselves into the host cell’s genome to replicate. At least three antiretroviral drugs used against H.I.V. have been shown in laboratory studies to inhibit XMRV, which has also been associated with prostate cancer.

Some chronic fatigue patients are already trying H.I.V. medications prescribed “off label.” One patient, Dr. Jamie Deckoff-Jones, a physician in Santa Fe, N.M., has been keeping a popular blog about her improving health while taking antiretrovirals prescribed by her doctor. “I think the sickest patients have the right to try the drugs,” she commented in an e-mail.

Dr. Alter was quick to note that “it’s not at all proven” that a retrovirus causes chronic fatigue syndrome. Instead, such an infection could result from underlying problems with the immune system.

Moreover, it remains unclear why only two research teams found evidence of retroviruses. One reason could be that different groups used varying testing and detecting methods; federal health officials have organized an effort to standardize the process.