Infectious mononucleosis (called "mono" for short) is caused by the Epstein-Barr virus (EBV), a virus that affects nearly everybody at some point. The disease is sometimes known as glandular fever, because it causes lymph glands to swell up. It's also called the "kissing disease" because kissing is a common method of transmission.
Before 5 years of age, 50% of individuals are infected by EBV. By 40 years of age, 90% of individuals are infected. Once you've caught the virus, it never really goes away. However, it can only cause symptoms in healthy people when it's still new in the body. After that it's kept in check by the immune system, though never completely eradicated.
Of course, nowhere near 90% of the population has suffered from mononucleosis. Half of all people are infected with EBV before age 5, and this age group hardly ever has symptoms beyond occasional mild tonsillitis. Unless their immune system collapses, they will never have mononucleosis. In the 5 to 30 years of age group, most studies have found that about 10% of people with EBV get the symptoms of mononucleosis. The exception is college students, who have rates of around 1 in every 2 cases of infection, which is several times higher than non-college students of the same age.
There are rare cases of mononucleosis occurring in older people, but usually the ones affected have weakened immune systems. Older people will usually have been infected much earlier in their lives. Such cases tend to be severe but not deadly.
In recent years, a link has been postulated between EBV and myalgic encephalomyelitis/chronic fatigue syndrome, but the latest studies seem to refute that. There is, however, a longstanding link with Burkitt's lymphoma, a cancer that occurs mostly in central Africa. EBV is also linked to other cancers such as Hodgkin's disease. EBV is one of very few viruses known to be capable of causing cancer.
There's also a weak link with nose and throat cancer. The small minority of people who don't carry EBV have a lower-than-average chance of developing this cancer.
EBV is a member of the herpes family. It's carried in the salivary glands and is spread by direct intimate contact such as kissing. Sneezes and coughs can also spread the virus but its transmission as an airborne pathogen is poor.
Sharing a house with someone who has mononucleosis is unlikely to result in infection. It's not nearly as contagious as the common cold. However, the virus can persist in the throat of an infected person for a long time. The virus can be found in the saliva in up to 15% to 25% of people who have been previously infected with the virus. Rarely, the virus can be transmitted through blood transfusion.
Symptoms and Complications
There are four symptoms traditionally associated with mononucleosis:
- swollen glands on the sides and back of the neck, under the arms and above the groin
- fever peaking each day in late afternoon or early evening, sometimes up to 40.5°C (105°F)
- sore throat
These symptoms arrive 4 to 8 weeks after infection. They're usually preceded by general unwellness, which may last about a week.
The infection itself lasts from 1 to 3 weeks, though about 2% of people have fatigue that lasts longer. The virus remains infectious in the saliva for several months, and never completely leaves the body.
Not everyone has all of the classic mononucleosis symptoms - some people have no symptoms. Many people just have swollen glands, and some just suffer fatigue. Other people may have a fever, a sore throat, and swollen lymph glands. Infants and young children usually only have a sore throat or tonsillitis, but they may have no symptoms at all.
A small percentage of people may experience jaundice (a yellowing of the skin) caused by the breakdown of red blood cells or liver problems. Some may develop a skin rash. Very rare complications such as encephalitis (brain inflammation) can also occur.
In about half of those who have mononucleosis with symptoms the spleen enlarges, and in about 20% the liver also swells. If you have mononucleosis, you'll be advised to avoid heavy lifting or strenuous sports for 3 months, because the spleen is fragile even if it isn't swollen. The organs slowly return to normal after the infection; however, there's a small but real chance of the spleen rupturing.
The most common, but still rare, complication of mononucleosis is rupture of the spleen. In about half of these ruptures, the person isn't exercising when it happens. Rupture of the spleen can sometimes be painless, but it leads to low blood pressure and shock.
Making the Diagnosis
Your doctor will ask you questions about your symptoms and perform a physical exam. The Epstein-Barr virus (EBV) is reliably detected by blood tests that look for antibodies and other cells that are only found in the presence of this infection.
Some doctor may choose not to test the blood for the virus since there's not much the doctor can do with the information. Blood tests may be done to check for other medical conditions that could cause similar symptoms.
It's important to eliminate the possibility of strep throat, which causes similar symptoms and could be treated with antibiotics. That's more easily done by testing for streptococcal bacteria with a throat swab than by testing the blood for EBV.
Treatment and Prevention
There's really nothing modern medicine can do about viral infections like mononucleosis. Fortunately, most cases are mild. Stay in bed for a few days, and don't hurry back to school or work.
Drink plenty of water and fruit juices to avoid dehydration. You can take various syrups to soothe a sore throat, and acetaminophen to control fever. Children should not be given acetylsalicylic acid* (ASA) when treating mononucleosis because of the possibility of Reye's syndrome, a dangerous brain inflammation.
Rare and severe symptoms, like a massively enlarged spleen or swelling of the airway to the lungs, are treated with corticosteroids to reduce inflammation. Ruptured spleens must be removed in an emergency operation.
There's little you can do to avoid mononucleosis, except not kissing people who've been diagnosed with the disease. Most carriers have no symptoms, and therefore aren't diagnosed. If you're an adult, chances are you've already had it without knowing it and are now largely immune from re-infection.
If you get mononucleosis, the most important thing is to listen to advice about taking it easy for 3 months afterwards. The risk of a ruptured spleen is small, but not so small as to be ignored.
*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.