Strong evidence that a virus may cause at least some cases of Alzheimer's disease could mean treatment and even prevention some day, but experts cautioned that the finding needs to be substantiated by more research.

"This is an interesting but quite preliminary observation," said Dr. David Drachman, chairman of the medical and scientific advisory board of the Alzheimer's Disease and Related Diseases Association.Dr. Laura Manuelidis said Thursday she and her colleagues at the Yale University School of Medicine in New Haven, Conn., that experiments involving hamsters indicate a virus played a role in the devastating disease.

"It is the strongest evidence yet that there may be a viral cause at least in some cases of Alzheimer's disease," said Manuelidis, an associate professor of neuropathology and neurosciences who published her findings in the Proceedings of the National Academy of Sciences.

Alzheimer's disease, which causes a devastating destruction of brain cells, affects an estimated 2.5 million Americans, killing 120,000 people each year. There is no effective treatment and the cause is unknown.

If additional research confirms a virus is the underlying cause of some forms of Alzheimer's, it could lead to a way to treat or prevent the disease, said Zaven Khachaturian of the National Institute on Aging in Bethesda, Md.

"It gives a clue for science to go on the attack - to look an infectious agent. Once you find it, you can find ways to treat it, to inoculate against it," Khachaturian said.

Some researchers already had suspected a virus may cause the disease, but previous studies had failed to substantiate that hypothesis.