In underdeveloped countries, people are exposed in early childhood when they are not likely to develop noticeable symptoms. In developed countries such as the United States, the age of first exposure may be delayed until older childhood and young adulthood when symptoms are more likely to result. For this reason, it is recognized more often in high school and college students. Symptoms include fever, sore throat, swollen glands, and feeling tired. Sometimes, the liver and spleen are affected and enlarged.
Duration is from one to several weeks.
A small proportion of affected people can take months to return to their normal energy level. There is no evidence that this is due to abnormal persistence of the infection in a chronic form. The disease is more severe in older adults, but very rarely is the disease fatal. Symptoms appear from four to six weeks after exposure. The virus is shed in the throat during the illness and for up to a year after infection.