Most people do not realize how common mononucleosis, the "kissing disease" is. In fact, mono is an illness that causes prolonged fatigue and limits regular activities for many people every year. And over 95% of all adults over age 40 have contracted the virus at some point in their lifetimes. But what is mononucleosis? What causes the condition? And who is at risk for developing mono?

What is mono?
Mononucleosis is a viral disease. Viruses are a very common type of infectious disease. Many of the most common human diseases are viral, caused by the smallest life-form existing, not larger than a single cell. In fact, viruses are small strands of DNA-like cell material that consists mostly of RNA and cannot survive without host cells. Therefore, mononucleosis is a type of viral disease that lives off a human host.

A person does not have to have symptoms of mono to spread EBV.  And the EBV virus is not spread through the air. In fact, you can live with a person who has mono and never become infected yourself.  Most people have been infected with EBV before, so they usually don't get mono when exposed to a person who has it. After a person has been infected with EBV, the virus may stay in their body for the rest of their life, but they will not get mono again.

Mono can be spread through:

• contact with saliva (kissing)
• mucus from the nose and throat
• tears

But what causes mono and who is at risk of contracting the virus?  Can you totally avoid getting mono?  How long does mono last?  We answer these questions and more in the next section on causes and risk factors here.