(HealthDay News) -- Once you contract mononucleosis, the virus behind it stays in your body, the Nemours Foundation says.
In fact, about 95 percent of adults have the virus inside them, Nemours says.
You won't always be contagious, but symptoms of the virus -- usually Epstein-Barr -- can resurface. Common symptoms include fatigue, fever, muscle pain, headache and sore throat.
Once you're infected, it can take four to seven weeks to have symptoms. But you are prone to infecting others well before then, Nemours says. Many people, despite harboring the virus, never develop symptoms.
After you recover, experts aren't sure for how long you're contagious.
They say the best thing you can do to prevent mono -- or most any germ -- is to wash your hands well and frequently.