Ask the doctor
Q. My teenaged granddaughter was diagnosed with mono. Is that just a kids' virus or can older people get it?
A. We need to distinguish between the illness, mononucleosis (mono), and the virus that most often is the cause of the illness, Epstein-Barr virus (EBV). Most human beings become infected with EBV early in life, typically in their teenage years. Once we are infected, the virus remains in our bodies for the rest of our lives. It lies "asleep" inside some of our cells, periodically "reawakening" to multiply and go on to infect other cells, and then it settles down again.
For the vast majority of us, when we first become infected, the virus causes just sniffles or no symptoms at all, according to research by myself and others. Some people (a minority) develop mono, an illness that typically lasts a few weeks and then goes away. In a very few people, usually years after the initial infection, the virus can trigger several different kinds of cancer.
How can one virus account for such a wide spectrum of illness? We don't have specific answers. The general answer is that we are all genetically programmed to respond to an infection with a particular microbe in a particular way, that the genetic program is different in each of us, and that the way our body responds to the microbe defines the illness. So the virus that likely caused your granddaughter's mono probably already lives within you, and has for most of your life. If, like your granddaughter, you had mono when you were young, that was the moment the virus entered your body. It remains within you, contained.
— by Anthony L. Komaroff, M.D.
Editor in Chief, Harvard Health Letter
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.