Rainer, valacyclovir has been trialled for MS (see Pubmed abstract below) and didn't do too well. My understanding of the research on viruses and MS is that while still inconclusive, reactivation of the virus does not seem to drive actual relapses or progression immediately. Instead, viruses might somehow play more of a triggering role earlier in the process...but I'd wager that no researcher would be willing to make a definitive statement about the role of viruses in MS...
A randomized clinical trial of valacyclovir in multiple sclerosis.
Mult Scler. 2005 Jun;11(3):286-95.
Friedman JE, Zabriskie JB, Plank C, Ablashi D, Whitman J, Shahan B, Edgell R, Shieh M, Rapalino O, Zimmerman R, Sheng D.
Department of Neurology, New York University School of Medicine, NY, NY 10010, USA. firstname.lastname@example.org
OBJECTIVE: The human Herpesvirus type-6 (HHV-6) has been implicated in multiple sclerosis (MS). Valacyclovir is an antiviral agent with an excellent safety profile. A two-year placebo-controlled, double-blind study was conducted to (1) ascertain if high-dose, prolonged treatment with valacyclovir would be safe and (2) observe if valacyclovir would delay the progression of MS clinically or by magnetic resonance imaging (MRI).
DESIGN/METHODS: Fifty-eight patients were stratified as to severity and randomly assigned to receive valacyclovir (3000 mg/day) or placebo for a period of two years. Patients were followed clinically over the two-year period by means of the Expanded Disability Status Scale (EDSS), the Ambulation Index (AI) and brain MRI scans. Patients underwent routine lab studies every three months. Patients continued on the medication for two years unless they had a sustained progression or repeated exacerbations.
RESULTS: No patient discontinued the study due to side effects or toxicity. In Relative Ranking of Progression, time to first attack, attack rate, and time to withdrawal there were trends (but not statistically significant) toward drug effect over placebo in the Severe clinical category. MRI evaluation showed no significant drug effect.
CONCLUSIONS: Although not statistically significant, positive trends were detected for acyclovir by clinical measures, but not by MRI.