The evidence for persistent viral infection by herpesviruses and others to be a significant cause of Alzheimer's disease is mixed and contradictory. There are clear and well understood mechanisms by which persistent infection can in principle contribute to neurodegeneration, but only some epidemiological data supports the a role for viral infection in Alzheimer's disease. It may be that the contribution is small, or emerges very slowly over a long time, or it may be that only a subset of patients exhibit the necessary biochemistry for persistent infection to play a major role in neurodegenerative disease. Once clinical trials start to show that no beneficial effect results from antiviral treatment, however, further investigations will likely slow to a minimal level of effort.
Various studies have found connections between herpes infections and Alzheimer's, including an autopsy study that found HSV1 DNA was often associated with amyloid plaques in the brains of people diagnosed with Alzheimer's. Additional studies have found that people treated for herpes infections were less likely to be later diagnosed with Alzheimer's than HSV-positive people who received no antiviral treatment. This raised hopes that herpes treatments could slow progression of Alzheimer's symptoms among patients. But the first clinical trial to test that theory has found that a common antiviral for herpes simplex infections, valacyclovir, does not change the course of the disease for patients in the early stages of Alzheimer's.
The trial included 120 adults, age 71 on average, all diagnosed with early Alzheimer's disease or mild cognitive impairment with imaging or blood tests that indicated Alzheimer's pathology. All participants had antibodies revealing past herpes infections (mostly HSV1, some HSV2). The participants were randomly assigned to take daily pills containing either valacyclovir or a placebo. The researchers measured the patients' memory functions and imaged the brain to look for amyloid and tau deposits associated with Alzheimer's and other structural changes. After 18 months, the researchers found that patients taking the placebo performed slightly better on cognitive tests than the valacyclovir group, but no other measures were significantly different.
"Our trial suggests antivirals that target herpes are not effective in treating early Alzheimer's and cannot be recommended to treat such patients with evidence of prior HSV infection. We do not know if long-term antiviral medication treatment following herpes infection can prevent Alzheimer's because prospective controlled trials have not been conducted."
Link: https://www.cuimc.co...tage-alzheimers
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