The Kissing Disease

A sensationalist American newspaper decided to sensationalize infectious mononucleosis (IM) with this headline, which is sure to sell papers.
In a sense, and to the extent that the causative agent—a virus—is easily transmitted through saliva droplets, IF is also transmitted by kissing on the mouth, as can happen with other infectious diseases such as the flu. However, IF is caused by a different virus, the Epstein-Barr virus, although sometimes the symptoms of the two diseases—especially in the early stages—do not allow for an easy differential diagnosis.

While it can occur at any age, IF is most common in children, adolescents, and young adults. It typically begins with a general feeling of malaise and fatigue, followed by fever and pharyngitis (inflammation of the throat)—which can sometimes be very severe and painful—accompanied by enlarged, easily palpable lymph nodes in the neck (cervical lymphadenopathy). These symptoms usually last one to two weeks, although they can persist much longer, especially the fatigue. In half of the cases, there is enlargement of the spleen (splenomegaly) and the liver (hepatomegaly). It is usually a benign condition with no specific treatment and almost always resolves on its own.

In some cases, it may lead to complications or present with moderate to severe symptoms: hepatitis (inflammation of the liver), hemolytic anemia (destruction of red blood cells), bleeding, splenic rupture, meningitis, paralysis, etc. In addition, the disease can also—and quite frequently—present itself solely as unexplained fatigue or as the enlargement of a single lymph node or a cluster of lymph nodes in the neck, without fever. Since this lymph node enlargement also occurs in lymphoma (a malignant tumor of the lymph nodes), it sometimes leads to a biopsy (surgical removal of the lymph node for examination)—a procedure that can be avoided if an accurate differential diagnosis has been made beforehand.

However, the diagnosis of this condition, its complications, or even the most common manifestations of IM can only be made by a clinical pathologist in a laboratory. This involves the microscopic examination of lymphocytes (blood cells) and a test with low sensitivity for the presence of antiviral antibodies—the well-known Monotest—which is negative in 50% of children and 20% of adolescents and adults with the disease. Therefore, the clinical-laboratory diagnosis is made by testing for antibodies specific to various antigens present in the structures of the Epstein-Barr virus (anti-EBV-VCA IgG and IgM antibodies; anti-EAD and anti-EBNA antibodies).
The combination of these results allows us to determine whether the disease is absent, whether we are dealing with an active infection, or whether only antibodies from a past, already resolved infection are present.