Infectious Mononucleosis

What is mononucleosis?

Mononucleosis, also called “mono,” is a common viral illness that can leave you feeling tired and weak for weeks or months. Mono goes away on its own, but lots of rest and good self-care can help you feel better.

What causes mono?

Mono is caused by the Epstein-Barr virus (EBV). It is most often seen in adolescents and young adults. Children can get the virus, but it often goes unnoticed because their symptoms are mild. Adults usually do not get mono, because they have immunity to the virus.

Mono can be spread through contact with saliva, mucus from the nose and throat, and sometimes tears. Because the virus can be spread through kissing, it has earned the nickname the “kissing disease.” If you have mono, you can avoid passing the virus to others by not kissing anyone and by not sharing things like glasses, eating utensils, or toothbrushes.

As soon as you get over mono, your symptoms will go away for good, but you will always carry the virus that caused it. The virus may become active from time to time without causing any symptoms. When the virus is active, it can be spread to others.

What are the symptoms?

The most common symptoms of mono are a high fever, a severe sore throat, swollen glands and tonsils, and weakness and fatigue. Symptoms usually start 4 to 6 weeks after you are exposed to the virus.

Mono can cause the spleen to swell. Severe pain in the upper left part of your belly may mean that your spleen has burst. This is an emergency.

How is mono diagnosed?

Your doctor will ask you questions about your symptoms and examine you. You may also need blood tests to check for signs of mono (monospot test) and the Epstein-Barr virus. Blood tests can also help rule out other causes of your symptoms.

How is it treated?

Usually only self-care is needed for mono.

• Get plenty of rest. You may need bed rest, which could keep you away from school or work for a little while.
• Gargle with salt water or use throat lozenges to soothe your sore throat.
• Take acetaminophen (such as Tylenol) or ibuprofen (such as Advil) to reduce fever and relieve a sore throat and headaches.
• Avoid contact sports and heavy lifting. Your spleen may be enlarged, and impact or straining could cause it to burst.

In severe cases, medicines called corticosteroids may be used to reduce swelling of the throat, tonsils, or spleen.

Frequently Asked Questions

Mono is caused by the Epstein-Barr virus (EBV).

Cytomegalovirus (CMV) causes some cases of a mono-like illness. Much less commonly, a mono-like illness is caused by different viruses, such as hepatitis B, rubella, and HIV. Toxoplasma gondii, a single-celled parasite, can also cause a mono-like illness.

How mono is spread

Epstein-Barr virus (EBV) can be found in saliva and mucus (and sometimes tears). EBV is not spread by casual contact. You can live in the same house with a person who has mono and never become infected with the virus. But a person who has a weakened immune system may be at higher risk for infectious mono. It's possible that people who have had mono can spread the virus even though they no longer have symptoms.

• EBV lives and grows in the nose and throat. Any fluid that comes from these parts of the body, including saliva, tears, or mucus, can be infected with the virus. The virus (EBV) is spread when people come in contact with infected fluids.
• EBV can be spread through intimate contact or sharing of saliva. (A brief kiss on the lips is not likely to spread EBV. It is spread when saliva from an infected person gets into another person's mouth.)
• You can get EBV if you share a drinking glass or eating utensils with an infected person (through sharing saliva).
• In rare cases, someone can get an infection after receiving blood from a person who is infected with EBV.
• Most people get infected with EBV at some point in their lives but never get mono symptoms. EBV "sleeps" (is dormant) in the body. It can become active from time to time and spread to others. When it reactivates, most people do not have symptoms. Many healthy people carry the virus and spread it every now and then throughout their lives. Lifetime carriers of EBV are the most common source of EBV infection.

Contagious and incubation period

• You can pass the Epstein-Barr virus (EBV) to others for several weeks or months during and after the time you are first infected with EBV. The virus can also become active and spread to others from time to time throughout your life.
• There is a small risk of spreading EBV through blood products. If you know you have mono, you should not donate blood.
• It takes 4 to 6 weeks for symptoms to develop after you come in contact with EBV. This is called the incubation period.

Not everyone infected with the virus that causes mono (Epstein-Barr virus, or EBV) has symptoms. This is especially true in young children, who may have a fever but no other symptoms. People between the ages of 10 and 24 are most likely to have obvious symptoms.^{1, 2}

The most common symptoms of mono are:

• Fever, which may range from 101°F (38.3°C) to 104°F (40°C), and chills.
• Sore throat, often with white patches on the tonsils (which may look like strep throat).
• Swollen lymph nodes all over the body, especially the lymph nodes in the neck.
• Swollen tonsils.
• Headache or body aches.
• A lack of energy and fatigue.
• Loss of appetite.
• Pain in the upper left part of the abdomen, which may indicate that the spleen has become enlarged.

These symptoms usually get better within one or two months.

Mono can cause a rash if you take antibiotics such as penicillin, ampicillin, or amoxicillin. These antibiotics are often prescribed for other causes of sore throat, such as strep throat, and might be prescribed for you before the doctor knows you have mono. The rash is not an allergic reaction.³

Mono may cause your spleen to swell to 2 or 3 times its normal size. An enlarged spleen occurs in up to half of those with mono.⁴ A blow to the abdomen can cause an enlarged spleen to rupture. To reduce this risk, avoid heavy lifting and contact sports for 3 to 4 weeks after you become ill with mono or until your doctor says it is safe. In very rare cases, the spleen may rupture on its own.

Symptoms of mono can be more severe and last longer in people who have an impaired immune system or a rare genetic condition called X-linked lymphoproliferative syndrome.

The symptoms of infectious mononucleosis, such as a sore throat and fever, are found in many other conditions as well.

Usually, mono is a mild illness that goes away without treatment after several weeks. When you have mono, your symptoms may come and go, and your symptoms may change with time.¹

• A sore throat is worst during the first 3 to 5 days and gradually improves over the next 7 to 10 days.
• Fever may last 10 to 14 days. Usually it is mild during the last 5 to 7 days. If you have a fever, you should stay home from work or school until the fever goes away. You can then go back to your normal activities if you feel up to it.
• Swollen glands may last up to 4 weeks.
• It may take several weeks (even months) for your energy level to return to normal. Don't try to rush this process. Pushing yourself too hard could make you feel worse. Give your body the rest it needs.

Mono can cause your spleen to enlarge, making it prone to injury. To reduce the risk of injuring your spleen, avoid heavy lifting and contact sports for 3 to 4 weeks after you become ill with mono (or until a doctor tells you it is okay).

If you know you have mono, you should not donate blood. Epstein-Barr virus (EBV) can be spread through blood products, although this is not common.

Complications of mono are rare but are most likely to develop in very young children, older adults who are in poor health, and people with impaired immune systems.

In the past infectious mononucleosis and chronic fatigue syndrome were thought to be caused by the Epstein-Barr virus. But it is now believed that even though both conditions have some similar symptoms, they are different diseases and chronic fatigue syndrome is not caused by the Epstein-Barr virus.

Mono is caused by the Epstein-Barr virus (EBV). You are at increased risk of getting mono if you:

• Are between the ages of 10 and 24, especially if you are in close contact with many people. In the United States, college students, nurses, and people in the military are most likely to get mono.
• Have intimate contact with a person who has mono or an active EBV infection. (A brief kiss on the lips is not likely to spread EBV. It is spread when saliva from an infected person gets into another person's mouth.)
• Share drinking glasses, eating utensils, dishes, or a toothbrush with an infected person. A person does not have to have symptoms of mono to spread EBV.

After you have been infected with EBV, the virus may stay in your body for the rest of your life, but you will not get mono again.

EBV is not spread through the air. You can live with a person who has mono and never become infected with the virus.

Most people have been infected with EBV before, so they usually don't get mono when exposed to a person who has it.

If you have been diagnosed with mono, seek care immediately if:

• You have severe pain in the upper left part of your abdomen. This may indicate that your spleen has ruptured. Rupture of an enlarged spleen caused by mono is rare. It is most likely to happen because of a blow to the abdomen, but it may sometimes happen even without such an injury.⁵
• Your tonsils become so swollen that you find it difficult to breathe or swallow.

If you have not been diagnosed with mono and you have a severe sore throat that has lasted longer than 2 to 3 days after trying home treatment, call your health professional within 1 to 2 days.

If you have not been diagnosed with mono and have tried home treatment for 7 to 10 days, contact your doctor if you have:

• A lack of energy.
• Body aches.
• Swollen glands.

Watchful Waiting

Most cases of mono do not require treatment, but you still need to take care of yourself until the illness goes away. You should see your doctor to make sure your symptoms are not caused by a treatable infection, such as strep throat. If it is certain you have mono:

• Get plenty of rest.
• Gargle with salt water or use throat lozenges to soothe your throat.
• Take nonprescription pain relievers to reduce fever and relieve a sore throat and headaches.
• Avoid contact sports and heavy lifting for 3 to 4 weeks after you become ill with mono (or until a doctor tells you it is okay). Mono can cause your spleen to enlarge, and these activities can increase your risk for injuring your spleen.

Who To See

The following health professionals can diagnose and treat mono:

• Family medicine doctor
• Pediatrician
• Internist
• Physician assistant
• Nurse practitioner

To prepare for your appointment, see the topic Making the Most of Your Appointment

A medical history and physical exam are the most important ways a doctor can diagnose mono. During the medical history and physical exam, your doctor will ask questions about your symptoms and possible exposure to the disease. Your doctor will also examine you for signs of the infection. This may include looking at your throat, checking your skin, and pressing on your abdomen.

Blood tests to help confirm the diagnosis include:

• Mononucleosis tests (including the monospot test and EBV antibody test). It is possible for the monospot test to come back negative early in the course of the infection (false negative).
• Complete blood count (CBC). A CBC may be done to rule out other infections or complications of mono.

Other tests may be done if complications of mono occur or if the mononucleosis tests are negative.

• Liver tests may be done to find out whether the virus has affected your liver.
• If the mononucleosis test is negative, your doctor may test you for an infection with cytomegalovirus (CMV) or other organisms. CMV can cause a mono-like illness.

Usually no treatment for mono is needed other than:

• Getting plenty of rest.
• Gargling with salt water or using throat lozenges to soothe your sore throat.
• Taking acetaminophen (such as Tylenol) or ibuprofen (such as Advil) to reduce fever and relieve a sore throat and headaches. Do not give aspirin to anyone under the age of 20, because its use has been linked with Reye's syndrome.
• Avoiding contact sports and heavy lifting to reduce the risk of injuring your spleen.

Without other treatment, most people recover from mono after several weeks. But for some, it may take several months before they regain their normal energy levels. This extended period of fatigue is not the same as having chronic fatigue syndrome.

In severe cases, corticosteroids may be used to reduce swelling of the throat, tonsils, or spleen. This type of steroid use may also decrease the overall length and severity of illness from infectious mono.

The virus that causes mono (Epstein-Barr virus) is not spread as easily as most people think. If you follow these tips, you can reduce the chance of spreading or catching mono.

• Don't kiss or share dishes or eating utensils with someone who has mono. (A brief kiss on the lips is not likely to spread Epstein-Barr virus. It is spread when saliva from an infected person gets into another person's mouth.)
• Don't donate blood if you have mono. Although it is unusual for the Epstein-Barr virus to be spread through blood, it is possible.

Self-care is usually all that is needed if you have mono. Unless you have a serious complication of mono (which rarely occurs), no medicine or treatment will speed your recovery. More than 95% of people with mono recover without problems.⁶ There are many steps you can take to ease the symptoms until you are back to normal.

• Listen to your body. Don't push yourself when you have mono. If you feel tired, it is important to rest and give your body a chance to heal.
• Rest in bed. You probably won't feel like working or going to school anyway, and rest is very important.
• Avoid contact sports and heavy lifting for 3 to 4 weeks after you become ill with mono (or until a doctor tells you it is okay) to reduce the risk of injuring your spleen.
• Take acetaminophen (such as Tylenol) or ibuprofen (such as Advil) to reduce fever and to relieve a headache and sore throat. Do not give aspirin to anyone under the age of 20, because its use has been linked with Reye's syndrome.
• Soothe your sore throat with cool liquids and saltwater gargles [1 tsp (5 g) of salt in 8 fl oz (237 mL) of water]. Hard candies or throat lozenges might help too.
• Drink plenty of fluids, especially if you have a fever. This will help prevent dehydration.

Your symptoms will gradually improve over 2 to 3 weeks. You should be able to return to your normal activities within about a month. Let your symptoms be your guide. You may need to adjust your school and work schedule to take advantage of times when you feel more energetic. If you feel better, try to get back to your routine sooner, but remember not to push yourself.

There are no specific medicines used to treat mono. Over-the-counter medicines may be used to help treat the symptoms of mono.

Medication Choices

Over-the-counter pain relievers, including acetaminophen (such as Tylenol) and ibuprofen (such as Advil), may be used to relieve headaches and a sore throat. Do not give aspirin to anyone under the age of 20, because its use has been linked with Reye's syndrome.

In severe cases, corticosteroids may be used to reduce swelling of the throat, tonsils, or spleen.

Some people get strep throat while they have mono (although mono does not cause strep throat). Strep throat is caused by a bacterial infection and can be treated with antibiotics, such as penicillin or erythromycin. Taking antibiotics such as ampicillin or amoxicillin to treat strep throat may cause a rash in many people who have mono.¹ A rash caused by antibiotics can often be a first sign that the person has mono. The rash is not an allergic reaction.

Antiviral drugs do not improve the symptoms of mono or shorten the length of the illness.⁵

What To Think About

Nonprescription medicines are commonly used to relieve symptoms, but they do not shorten the duration of the illness. Aspirin should not be used to treat symptoms of mono in people under the age of 20, because it is linked to a serious disease known as Reye's syndrome.

There is no surgical treatment for mono. Emergency surgery may be needed to remove a ruptured spleen if this complication occurs.

There is no other treatment for mono.

Online Resources

Organization

• Chronic Fatigue Syndrome
• Fever, Age 4 and Older
• Sore Throat
• Swollen Glands and Other Lumps Under the Skin
• Weakness and Fatigue

Citations

1. Johannsen EC, et al. (2005). Epstein-Barr virus (infectious mononucleosis). In GL Mandell et al., eds., Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 6th ed., vol. 2, pp. 1801–1820. Philadelphia: Elsevier.

2. Hirsch MS (2007). Herpesvirus infections. In DC Dale, DD Federman, eds., ACP Medicine, section 7, chap. 26. New York: WebMD.

3. American Academy of Pediatrics (2006). Epstein-Barr virus infections (infectious mononucleosis). In LK Pickering et al., eds., Red Book: 2006 Report of the Committee on Infectious Diseases, 27th ed., pp. 286–288. Elk Grove Village, IL: American Academy of Pediatrics.

4. American Public Health Association (2004). Mononucleosis, infectious. In DL Heymann, ed., Control of Communicable Diseases Manual, 18th ed., pp. 373–375. Washington, DC: American Public Health Association.

5. Jenson HB (2000). Acute complications of Epstein-Barr virus infectious mononucleosis. Current Opinion in Pediatrics, 12(3): 263–268.

6. Epstein-Barr virus (2001). In WR Wilson et al., eds., Lange's Current Diagnosis and Treatment in Infectious Diseases, pp. 408–412. New York: McGraw-Hill.

Other Works Consulted

• Cohen JI (2003). Epstein-Barr virus infections. In IM Freedberg et al., eds., Fitzpatrick's Dermatology in General Medicine, 6th ed., vol. 2, pp. 2094–2099. New York: McGraw-Hill.