Description. Mononucleosis is a widespread viral illness among young adults. The virus that causes mononucleosis is transmitted via mucus or saliva, either through direct contact (hence, the nickname, the “Kissing Disease”) or via airborne droplets or saliva or mucus.The usual symptoms of mononucleosis are fever, sore throat, swollen lymph nodes in the neck, fatigue, and general discomfort.he virus that causes mononucleosis is transmitted via mucus or saliva, either through direct contact (hence, the nickname, the “Kissing Disease”) or via airborne droplets or saliva or mucus.