Multiple infectious pathogens have been associated with Alzheimer's. Medication may reduce the risk of dementia by suppressing several types of herpes viruses. Acyclovir 200 mg per day, and/or Amenamevir 100 mg per day may be effective. It is unknown if pathogens slowly eat away at the brain tissue over many years, or very quickly as the immune system senesces in old age. Regardless, cognitive impairment may only appear when very little brain tissue is left in certain areas. As with other body systems, problems may not appear until 80 to 95% of functional tissue is gone, by then it is "too late." To avert brain deterioration reaching "end-stage" disease, taking daily medication beginning at age 60 to 65 is reasonable. Persons at high risk may consider starting earlier. Brain damage and neuron loss is permanent, so the only way to keep the brain working is to prevent initial break down. Research studies support antiviral medication to prevent dementia. Further validation is forthcoming as several clinical trials are in progress to determine effectiveness of this approach. This book is a new edition of Dr. Horne's Prevention and Treatment for Alzheimer's Dementia Based on the Infection Model; a Discussion, with a new chapter on helicase primase inhibitor drugs.