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Volume CXXXIII, Number 10 |
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Mono not easy to detect
JEFF BENSON, M.D.
DUDLEY COE HEALTH CENTER
Dear Dr. Jeff: I was seen recently at the Health Center for a sore throat. You thought it might be mono, and did some blood tests. They came back negative, and you said that didn't mean I didn't have mono. What's up with all of this?-M.W.
Dear M.W.: Infectious mononucleosis is a contagious illness, usually characterized by fever, sore throat, swollen lymph nodes, weakness, and fatigue. Mono is caused by Epstein Barr Virus (EBV), a member of the Herpesvirus family. EBV infects the cells which line your nose and throat, as well as B cell lymphocytes (one type of white blood cell). Viral DNA is incorporated into B cell DNA, and these transformed B cells carry the infection to other organs, including your liver and spleen.
Some of these infected B cells become "immortalized," forever harboring the viral genome. The full import of this transformation is not yet well understood, but it has been linked to a variety of disorders, including chronic fatigue syndrome and depression in this country and certain childhood malignancies in Africa.
About 12 percent of susceptible college-age men and women are infected each year with EBV, and about half of them develop full-blown mono. That means that nearly one in 40 college students will come down with mono every year.
Transmission of EBV occurs through contact with infected saliva (hence mono is known as the "kissing disease"). The incubation period is about 30-45 days, and the illness typically lasts two to four weeks. The period of communicability, however, can be quite prolonged. Viral shedding in saliva begins during the incubation period, and can persist for a year or more after the infection has apparently resolved.
There is no cure for EBV, but fortunately mono does not usually need to be treated. Sometimes it causes so much painful swelling of the tonsils that a brief course of Prednisone is necessary. Most often, treatment is supportive: rest and plenty of fluids. Mono causes inflammation of your liver, so alcohol and medications which can affect your liver (e.g. Tylenol and Accutane) must be avoided. Inflammation of your liver, in turn, can cause swelling of your spleen, so contact sports should also be avoided.
Diagnosis of mono is not always straightforward. Infection with EBV causes B cells to produce a variety of antibodies, among them the "heterophile antibody." Most "mono tests" look for this heterophile antibody in your serum.
Test results, however, can be difficult to interpret. While the antibody is detectable in about 90 percent of people at some point during their illness, it may appear earlier or later. It usually disappears three or four months after the infection has run its course, but may persist longer. In other words, a monospot test might be falsely negative if done too early, or falsely positive if done too soon after a prior (and resolved) infection-and "too early" might mean anywhere from one to four weeks, and "too soon" might mean six months or more!
Heterophile antibodies are not protective against EBV itself. They are produced "by order" of incorporated viral DNA, and in fact react with the red blood cells of other species, like hamsters and sheep (hence "heterophile"). Antibodies directed against EBV itself are also made soon after infection, but only by uninfected T cells and B cells. These other antibodies are felt to confer long-term immunity, and their presence is also more straightforwardly diagnostic of an acute EBV infection. Unfortunately, they can be detected only by laboratory tests which are less common, and far more expensive.
Diagnosis of mono can be a little tricky. Usually, with a little time and repeated lab tests, we can sort it out. Mono may cause its fair share of misery, but it is fortunately almost always short-lived.
Be well!
Jeff Benson, M.D.
Dudley Coe Health Center
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