Infectious disease caused by the Epstein-Barr herpes virus, transmitted in saliva by direct contact (hence the old name ‘kissing disease’) or by coughing in the faces of other people. One to six weeks can pass between infection and outbreak of the disease. Later stages vary from person to person. There is often a general feeling of malaise, associated with sore throat; swelling of the lymph nodes of the neck, armpits and groin; and gradually increasing fever. The spleen may be enlarged and the liver may be affected, possibly causing jaundice. Other symptoms are headache, stiff neck, inflammation of the eyes, nausea, vomiting, and sometimes a red skin eruption. The disease can last for several weeks or months; fever and swelling usually disappear after a few weeks, but the patient may feel tired and listless for a longer period. In extreme cases depression can occur because the patient has been feeling unwell for so long. Other possible complications are anaemia, meningitis and inflammation of the heart or kidneys. Diagnosis is by extensive physical examination to find the above symptoms. Laboratory blood tests show large quantities of special white blood cells known as monocytes; such tests can also detect the Epstein-Barr virus, possible disturbances in liver function, anaemia, and so on. There is no specific treatment because it is a virus infection; in general bed rest is advisable and possibly a special diet if there are liver problems. The patient becomes immune for life after having suffered from the disease once.