INFECTIOUS MONONUCLEOSIS

Mono

Infectious Mononucleosis (Mono) is the kissing disease. It’s a weird condition. It’s usually caused by the Ebstein-Barr virus (EBV), although CMV can sometimes cause Mono. The Kissing disease (transmitted by saliva) typically hits teenagers the hardest. EBV likes to infect the throat (sore throat is the usual presenting complaint) as well as infect individual B-cells, using an apparatus that hooks onto the surface receptor CD21 (Must be 21 to drink a Beer in a Barr). The zombie B-cells will travel to the lymph nodes (where they will cause hyperplasia of the paracortex, because T-cells live here, and they are waging a war against the zombie B’s) and to the spleen (here the T-cells reside in the Periarterial Lymphatic Sheath). Splenomegaly is classic with mono. Mono is pretty special for causing posterior cervical lymphadenopathy (which is pretty rare), although keep in mind that lymphadenopathy does occur in other locations too. 

Mono is characterized by an elevated white blood cell count with a high lymphocyte count. The majority of the white cells are killer T cells with an unusual appearance. These are called “reactive lymphocytes,” “Downy cells” or “atypical lymphocytes” and they appear quite different than regular lymphocytes. They have more cytoplasm and a larger nucleus, which makes them look like monocytes. We all associate Mono with B-cells, but keep in mind that the “atypical lymphocytes” are actually those killer T-cells that are fighting against the infected B cells. 

Mono has a very weird lab finding. If you take the blood of a Mono patient, and inject it into a sheep or horse, then the animal will suffer a transfusion reaction! That’s because infected Mono B cells pump out (useless) antibodies that happen to bind to the antigens on horse and sheep RBCs. This peculiar phenomenon is utilized by labs to detect Mono (since animal blood is cheap). The trade name of the test is Monospot, but trade names aren’t on the boards, so we should familiarize ourselves with the technical name which is the heterophile antibody agglutination test. Hetero- means different and -phile means love. Our antibodies love a different species (ew). 

Complications of Mono

• To prevent rupturing their enlarged spleens, patients should avoid contact sports until the resolution of symptoms. 

• Mono causes a rash when amoxicillin is used to treat it

• Mono can lie dormant in B cells for the rest of your life. Mono symptoms will typically recur 2 or 3 times in the patient’s life. This also increases the likelihood of a future lymphoma (especially if they develop an immunodeficiency down the road)

• Mono can cause IgM Autoimmune Hemolytic Anemia.