Anju Goel, MD, MPH, is a board-certified physician who specializes in public health, communicable disease, diabetes, and health policy.
Infectious mononucleosis (mono) is a condition usually caused by the Epstein-Barr virus (EBV) or, less commonly, cytomegalovirus (CMV).
Mono is sometimes called the "kissing disease" because it is spread through saliva, shared drinking cups and utensils, and close contact.
Symptoms (fever, sore throat, swollen lymph glands, enlarged tonsils, and extreme fatigue) appear approximately four to eight weeks after exposure. Infected persons "shed" the virus in their saliva and can be contagious for about six months. The virus eventually becomes dormant but never fully goes away. It can be potentially activated again if your immune system is weakened.
Mono is treated with rest and symptom management. Prescription drugs are rarely needed.
Infection by the Epstein-Barr virus (EBV) is the most common cause of mononucleosis, but other viruses can cause mono-like illnesses too, such as cytomegalovirus (CMV).
Mononucleosis is primarily spread through bodily fluids, especially saliva, but also through mucus, blood, semen, and vaginal secretions. Sharing a cup, straw, or eating utensil can contribute to the spread of EBV. Blood transfusions and organ transplantations can also spread the virus. One out of 4 teens or young adults who get infected with EBV will develop mono.
The incubation period for mono is four to eight weeks, which means that symptoms set in at least a month after you've been exposed to the virus. Some symptoms may only last for a few days, while others, such as fatigue, may persist for months. Mono symptoms last for two to four weeks in most people.
In most cases, you'll only get mono once, but as the EBV virus stays in your body for the rest of your life, it is possible that mono could make a comeback. This is rare, and generally only likely if your immune system is weakened by another infection such as HIV, an organ transplant, or pregnancy. It's also possible to get mono from a virus other than EBV, even if you already have EBV.
A test analyzing a blood sample for the presence of antibodies, which are produced by the immune system in response to an infection. While the CDC no longer recommends using the monospot antibody test to diagnose mono, many still administer this test alongside a symptom assessment to help confirm a diagnosis. The heterophile antibody test is primarily used for diagnosis.
Unusual looking white blood cells. In mononucleosis, lymphocyte counts may not only be elevated, but the cells are also atypical in appearance. It's often the earliest sign of EBV infection. Under the microscope, a percentage of white blood cells (WBC) will have more cytoplasm, making them larger. The larger cytoplasm may appear to be indented by surrounding red blood cells.
A virus in the herpes family affecting more than 95% of the world's adult population. In most cases, EBV is asymptomatic, but it may lead to mononucleosis, and is linked to autoimmune conditions such as multiple sclerosis and lupus. EBV infection is also linked to an increased risk of certain cancers, like Hodgkin lymphoma, Burkitt lymphoma, and stomach cancer.
An inflammatory liver condition commonly caused by a viral infection. The liver is often mildly affected in cases of EBV/mono, but sometimes this results in acute hepatitis with or without jaundice. This occurs mostly in older adults, but it may rarely occur in younger people.
A metric assessing the number of white blood cells (WBC) present in a blood sample as part of a complete blood count (CBC). If a high number of WBC are present, it may indicate your body is fighting off an infection. A high WBC count is commonly seen when diagnosing mononucleosis, especially an elevated lymphocyte count (known as lymphocytosis).
Centers for Disease Control and Prevention. Epstein-Barr Virus and Infectious Mononucleosis. About Infectious Mononucleosis. Updated September 28, 2020.
Centers for Disease Control and Prevention. Epstein-Barr Laboratory Testing. Updated May 10, 2018.
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