What Causes Mono? Mononucleosis is caused by the EBV. According to the Centers for Disease Control and Prevention (CDC), EBV is a member of the herpes virus family and is one of the most common viruses to infect humans around the world. The virus is spread through direct contact with saliva from the mouth of an infected person and cannot be spread through blood contact. You can be exposed to the virus by a cough or sneeze, by kissing, or by sharing food or drinks with someone who has mono.