Mononucleosis aka "mono", caused by Epstein-Barr virus (EBV). Spreads through contact with saliva, mucus from nose/throat, tears, sharing eating utensils or toothbrushes. Treatment: rest, salt water gargle, Tylenol, or corticosteroids in severe cases. Avoid heavy lifting/contact sports as spleen may be enlarged and straining/impact could cause it to burst.
The CDC notes that "Epstein-Barr virus (EBV), also known as human herpesvirus 4, is a member of the herpes virus family. It is one of the most common human viruses. EBV is found all over the world. Most people get infected with EBV at some point in their lives." (See the CDC fact sheet on Mono.) To learn more about EBV and infectious mononucleosis click here: http://novirin.com/EBV.php