This common and very infectious virus is sometimes nicknamed "the kissing disease" because of the form of transmission. It is also often called simply "mono". Mononucleosis is caused by the Epstein-Barr virus, and it often produces a sore throat, fever, and fatigue. It is estimated that over 90% of adults in the western world have been exposed to the virus.

The virus is spread via saliva and produces symptoms which can last up to three weeks. Plenty of rest and fluids is recommended and the patient should not participate in rigorous activites or a ruptured spleen could result as a complication of Mononucleosis.