WASHINGTON — A U.S. government study has uncovered a family of mouse viruses in some people with chronic fatigue syndrome, raising still more questions about whether an infection may play a role in the complicated illness.

Monday’s study does not prove that having any of these viruses causes harm, stressed co-author Dr. Harvey Alter of the National Institutes of Health.

But it strengthens suspicions, and the government has additional research under way to determine if the link is real or not.

The virus connection first made headlines last fall when Nevada researchers reported finding a specific type, named XMRV, in the blood of two-thirds of the 101 chronic fatigue patients they tested. But several other studies, including one from the Centers for Disease Control and Prevention, failed to find XMRV virus in patients, making researchers wonder if this was a false alarm.

Various viruses have been linked to chronic fatigue over the years only to fall by the wayside as potential culprits in the mysterious illness thought to afflict about 1 million Americans.