Alzheimer's 'may be caused by a virus'

Alzheimer's may be triggered by a virus, according to a new study that discovered people with the disease had twice the level of the common herpes bug.

Researchers say their findings suggest that a controversial hypothesis that viruses are involved in dementia may be correct.

The American team found 'unusually high' levels of two strains of human herpes virus 6A (HHV-6A) and human herpes virus 7 (HHV-7) in brains of Alzheimer's sufferers compared to those free of the disease.