If you were exposed to the virus as a child, you may already have immunity to it. The risk of transmission is present, especially through sharing saliva, so it is wise to avoid doing so with someone who has mononucleosis. The risk of transmission through sexual contact without saliva exchange is minimal. If you do contract the virus, symptoms may not appear for about a month. Some people may not experience any symptoms at all, and if you have had the virus in the past, you may be immune to it.