Phages break up plaques.

Phages, which are viruses that infect bacteria, cut through plaques in the brains of mice engineered to develop a disease similar to Alzheimer's. That action helped the rodents recover.

"Phages dissolve plaque," says Beka Solomon of Tel Aviv University in Israel. "We saw improvements in memory and smell tests" of the mice.

Solomon worked with a phage that infects Escherichia coli bacteria. It's long and thin and is naturally attracted to the flat proteins that form plaques in the brains of Alzheimer's patients. Scientists generally agree that these plaques cause the disease.

Solomon gave 100 of the mice monthly doses of the phage in a nose spray. The phages slipped into the brain via the olfactory bulb, which is where Alzheimer's-like plaques first appear in both people and mice. One of the first symptoms of the disease, in fact, is a loss of the sense of smell.

The treated mice regained their senses of smell, and their memories improved. When Solomon examined the mice after 1 year of treatment, they had 80 percent fewer plaques than untreated mice did.

Immune cells in the brain cleared the phages along with the plaque fragments, says Solomon. She found no evidence of harmful inflammation in the other organs of the animals, which had been a possibility because the immune system usually reacts strongly to phages.

"The phages are going into the brain, they do their work," and then the body gets rid of them, Solomon says. She delivered the phages through the nose because injecting them elicits a swift and dangerous inflammatory reaction.

Solomon plans to start a company to raise funds for a trial of phages in people.