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Volume CXXXII, Number 2 |
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Mononucleosis
JEFF BENSON
FACULTY CONTRIBUTOR
Dear Dr. Jeff: "I was recently seen at the Health Center for a sore throat. You thought it might be mono. You did some blood tests, which came back negative, but you said that didn't mean I didn't have mono. I'm confused!" C.L.
Dear C.L.:
Infectious Mononucleosis is a contagious illness characterized by fever, sore throat, swollen lymph nodes, and often severe weakness and fatigue. It is caused by Epstein Barr Virus, a member of the Herpesvirus family, which infects the cells lining your nose and throat as well as B cell lymphocytes (white blood cells). Viral DNA is incorporated into B cell DNA, and these transformed B cells carry the infection to other organs in your body, especially your liver and spleen.
Early childhood infection with Epstein Barr Virus is common (pretty well
the norm in the developing world), and usually results in a barely noticeable
"cold". In the United States, about 30 percent of children have
been infected by the age of 5, and another 25 percent by the end of high
school. About 12 percent of susceptible college-age men and women are
infected each year with the virus, and about half of them develop clinical
mononucleosis. That means that nearly 1 in 50 students come down with
mono every year.
Transmission of Epstein Barr Virus takes place through contact with infected
saliva (hence mono as the "kissing disease"). The incubation
period is about 30 to 45 days, and the illness typically lasts two to
four weeks. The period of communicability, however, is prolonged, and
viral shedding in saliva begins during the incubation period, and may
persist for a year or more after the infection has resolved.
Mono does not usually need to be treated. Sometimes, though, it causes your tonsils to enlarge so much and to become so painful that a brief course of Prednisone is indicated. Generally, 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 during your illness.
When B cells are infected with Epstein Barr Virus, they produce a variety of new antibodies, among them the "heterophile antibody". Most "mono tests" (for instance, the "Monospot" test we use at the Health Center) look for this heterophile antibody in your serum. This may seem straightforward enough, but test results 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 it 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 1 to four weeks, and "too soon" might mean six months or more!
This heterophile antibody is kind of interesting. It is not protective against the Epstein Barr Virus itself. It is produced by infected B cells, under the "orders" of the incorporated viral DNA, and it reacts with the red blood cells of other species (like hamsters and sheep): hence "heterophile". Antibodies directed against Epstein Barr Virus 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 infection. Unfortunately, they can be detected only by laboratory tests, which are less common, and far more expensive.
B cells infected with Epstein Barr Virus have an atypical appearance under the microscope, and the presence of large numbers of "atypical lymphocytes" is another important laboratory sign of Infectious Mononucleosis. It is not, however, terribly specific. In fact, many different viral illnesses also cause an increase in atypical lymphocytes, including those which also cause mono-like illnesses nearly indistinguishable from Epstein Barr Virus infection (like Cytomegalovirus, Human Herpesvirus Type 6, Toxoplasmosis, and Rubella).
So, diagnosis of mono can be a little complicated. Usually, with a little time and repeat lab tests, we can figure it out. Mono may cause a fair amount of short-term misery, but it is, fortunately, almost always short-lived, and rarely causes complications.
Be well!
Jeff Benson, M.D.
Dudley Coe Health Center