As viruses go, herpes is a particularly devilish bugger. The ancient Greeks were among the first to record the sores it causes (the virus's name is derived from a Greek word meaning "to creep"), and today the microbe is ubiquitous. As many as 85 percent of us have been infected by it, though experts say as few as 15 percent show symptoms. Worse, once you have it, you have it forever: After the initial infection, the virus lies dormant in your peripheral nervous system, occasionally flaring up during periods of stress, illness, or fatigue. But it never completely disappears.

And it's that fact—herpes as the viral equivalent of The Thing That Wouldn't Leave—that lies at the heart of the herpes-Alzheimer's relationship. Research suggests that as we age, HSV-1 actually spreads to our brains, where in certain people, Itzhaki theorizes, it can cause the buildup of deposits—known as amyloid plaques and neurofibrillary tangles—that attack and destroy the cells responsible for memory, language, and physical functions. In short, those people develop Alzheimer's.

It's a provocative theory, one that would sound preposterous if it weren't for the steadily accumulating evidence. Last January, for instance, Itzhaki and her colleague, Matthew Wozniak, Ph. D., published a study in the Journal of Pathology in which they searched for the presence of the herpes virus in people's brains. They found that it resided in 90 percent of the amyloid plaques.

"The link between herpes and Alzheimer's has been there for a while, but more people are starting to pay attention," says Howard Federoff , M.D., Ph.D., an expert on neurodegenerative diseases and the executive dean of the school of medicine at Georgetown University. "It's no longer just a curiosity."

Unfortunately, while the theory may be on more researchers' radar, it's perhaps becoming a blip in the one area that matters most: the fight for funding. Sure, on the surface, the possible discovery of a cause for Alzheimer's looks like Nobel-caliber news because it suggests a way forward in treating a disease that scientists have struggled—largely unsuccessfully—to understand. What's more, if a new treatment does emerge, it could be just in the nick of time: Thanks to a combination of changing demographics and longer life spans, experts are predicting nothing less than an Alzheimer's epidemic in the decades ahead.

And yet all the promise held in the herpes connection may vanish as quickly and completely as the memories of an Alzheimer's patient. That's because despite Itzhaki's nearly 20-year struggle to get her work noticed, an entrenched Alzheimer's research establishment remains skeptical. Worse, she now finds herself on the brink of having to shut down what may be the most promising avenue of investigation in ages.