The results in people taking valaciclovir will be compared with those in people not taking the drug. People whose results show the virus has disappeared from the body will continue to be followed twice a year for 5 years with the blood and gargling tests to continue to look for evidence of virus. Also, people who develop symptoms resembling mononucleosis (e.g., enlarged lymph nodes with fever and sore throat) will be asked to have their blood tested for the virus.