The most well known symptom of “mono“ is extreme fatigue, forcing the infected person to nap frequently. If you experience such extreme fatigue accompanied by other symptoms, such as swollen lymph glands and spleen, sore throat, fever, loss of appetite, and muscle aches, you may want to get tested for mono. The basis for testing whether you have mono is the presence of antibodies produced by white blood cells. Many people infected with mono don’t get sick, or have such mild symptoms they don’t know they have it. EBV is usually in the body 30-50 days before an infected person develops symptoms. Surprisingly, 80-95% of adults in the US have been infected by the time they’re 40, but only about 20% know they’ve had mono.