WASHINGTON (Reuters) - A virus that causes ulcers that appear next to the mouth or so-called "fever pills" may be responsible for at least half of the cases of Alzheimer's disease, scientists said.

Data from a leading Alzheimer's disease expert who spent more than 25 years at the University of Manchester investigating possible links showed that virus-causing viruses increase the risk of Alzheimer's disease, while clinical trials will help some cases and prevent their appearance by using anti-viral drugs when they appear.

The review concluded that treating people suffering from fever pills with antiviral drugs significantly reduces the risk of developing Alzheimer's disease.

However, charities are calling for more research, so it is not an issue for people who suffer from fever pills on an ongoing basis, while patients are urged to follow up with doctors if they recur.

"The causes of dementia are incredibly complex, and in most cases, one factor can not be identified," said Dr. James Pickett, head of research at the Alzheimer's Society.