When I was in college, several of my friends developed infectious mononucleosis, commonly known as mono. They were sick for months. They were always exhausted, and several of them lost a lot of weight (and they weren’t overweight before getting sick). I contracted it as well, but I must have had a mild form, as I only felt bad for a week or two.

This illness commonly affects high school and college athletes, so it’s worthwhile to answer some of the common questions about infectious mononucleosis and participation in sports.

Who develops infectious mononucleosis?

This illness most commonly occurs in people between the ages of 15 and 24. Rarely do older athletes develop it.

How do you contract infectious mononucleosis?

The Epstein-Barr virus is transmitted through saliva. This fact accounts for the illness being commonly known as the “kissing disease.” Since transmission occurs through saliva, an athlete with infectious mononucleosis does not need to be isolated from other people. Teammates should wash their hands and use their own water bottles.

What are the common symptoms of mono?

For the first few days, an athlete with infectious mononucleosis might experience fatigue, a lack of appetite, and a general sense of not feeling good. Then the classic symptoms of mono develop, including a sore throat, fever and swollen lymph nodes, especially in the neck. Fatigue can range from a mild lack of energy to total exhaustion. Jaundice and a rash are much less common symptoms.

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Why is the spleen enlarged in infectious mononucleosis?

The virus targets a certain type of blood cell – the lymphocyte – and causes them to proliferate. The spleen tries to filter the lymphocytes and enlarges. The spleen often enlarges beyond the rib cage, making it susceptible to rupture in contact and collision sports.

How can a physician determine the spleen size?

Physical exam often does not detect splenic enlargement. Ultrasound of the spleen is felt to be the best radiology study. Even with ultrasound, since spleen size can vary between different people, determining when the spleen is enlarged and at risk for rupture in sports is challenging.

How is infectious mononucleosis treated?

There’s no antibiotic or antiviral medication indicated for treatment. Management is based on treating symptoms. Hydration, anti-inflammatory medications and rest are generally the main recommendations. Light exercise is even allowed a few weeks into the illness. Infectious mononucleosis does resolve on its own, but some patients can have symptoms for 2 to 3 months or more.

When can an athlete return to sports with mono?

Generally an athlete must overcome the fever, fatigue and pharyngitis. Most athletes don’t feel well enough to play in the first few weeks, so playing sports in the first 21 days, when the risk of spleen rupture is highest, is rarely an issue.

An athlete usually can start light exercise as he (or she) starts to feel better. He can gradually increase activity as tolerated.

When he can play contact or collision sports is more controversial due to the risk of splenic rupture. Since it can be difficult to determine when the spleen has returned to its normal size, many physicians recommended avoiding these sports for at least the first three months after contracting infectious mononucleosis.

Reference:
Becker JA, Smith JA. Return to play after infectious mononucleosis. Sports Health. 2014 May;6(3):232-8.