Symptoms are mono are...
Fever—this varies from mild to severe, but is seen in nearly all cases.
Tender and enlarged/swollen lymph nodes—particularly the posterior cervical lymph nodes.
Sore throat—White patches on the tonsils and back of the throat are often seen
Muscle weakness and Mental fatigue (sometimes extreme)
Additional symptoms include:
Enlarged spleen (splenomegaly, which may lead to rupture) and/or liver (hepatomegaly)
Abdominal pain - a possible symptom of a potentially fatal rupture of the spleen.
Loss of appetite
Dizziness or disorientation
Uncontrolled shaking at times
Unable to swallow due to enlarged tonsils
Supra-orbital oedema—the eyes become puffy and swollen—may occur in the early stages of infection
After an initial prodrome of 1-2 weeks, the fatigue of infectious mononucleosis often lasts from 1-2 months. The virus can remain dormant in the B cells indefinitely after symptoms have disappeared, and resurface at a later date. Many people exposed to the Epstein-Barr virus do not show symptoms of the disease, but carry the virus. This is especially true in children, in whom infection seldom causes more than a very mild cold which often goes undiagnosed. Children are typically just carriers of the disease. This feature, along with mono's long (4 to 6 week) incubation period, makes epidemiological control of the disease impractical. About 6% of people who have had infectious mononucleosis will relapse.
Mononucleosis can cause the spleen to swell. Rupture may occur without trauma, but impact to the spleen is also a factor. Other complications include hepatitis (inflammation of the liver) causing elevation of serum bilirubin (in approximately 40% of patients), jaundice (approximately 5% of cases), and anemia (a deficiency of red blood cells). In rare cases, death may result from severe hepatitis or splenic rupture.
Although most cases of mononucleosis are caused by the E.B. virus, the condition is defined by the clinical presentation and laboratory findings. Cytomegalovirus can produce a similar illness, usually with less throat pain, and also generate atypical lymphocyte proliferation. In recent years, as precise virological and serological studies are more commonly done to identify the actual causative virus, some clinicians have taken to use "mononucleosis" to refer only to the E.B. virus cases. Symptoms similar to those of mononucleosis can also be caused by adenovirus, acute HIV infection and the protozoan Toxoplasma gondii