Infectious mononucleosis
Infectious mononucleosis, also known as glandular fever, is an infection usually caused by the Epstein–Barr virus. Most people are infected by the virus as children, when the disease produces few or no symptoms. In young adults, the disease often results in fever, sore throat, enlarged lymph nodes in the neck, and fatigue. Most people recover in two to four weeks; however, fatigue may last months. The liver or spleen may also become swollen, and in less than one percent of cases splenic rupture may occur.
While usually caused by the Epstein–Barr virus, also known as human herpesvirus 4, which is a member of the herpesvirus family, a few other viruses and the protozoon Toxoplasma gondii may also cause the disease. It is primarily spread through saliva but can rarely be spread through semen or blood. Spread may occur by objects such as drinking glasses or toothbrushes, or through a cough or sneeze. Those who are infected can spread the disease weeks before symptoms develop. Mono is primarily diagnosed based on the symptoms and can be confirmed with blood tests for specific antibodies. Another typical finding is increased blood lymphocytes of which more than 10% are reactive. The monospot test is not recommended for general use due to poor accuracy.
There is no vaccine for EBV; however, there is ongoing research. Infection can be prevented by not sharing personal items or saliva with an infected person. Mono generally improves without any specific treatment. Symptoms may be reduced by drinking enough fluids, getting sufficient rest, and taking pain medications such as paracetamol and ibuprofen.
Mononucleosis most commonly affects those between the ages of 15 and 24 years in the developed world. In the developing world, people are more often infected in early childhood when there are fewer symptoms. In those between 16 and 20 it is the cause of about 8% of sore throats. About 45 out of 100,000 people develop infectious mono each year in the United States. Nearly 95% of people have had an EBV infection by the time they are adults. The disease occurs equally at all times of the year. Mononucleosis was first described in the 1920s and is colloquially known as "the kissing disease".
Signs and symptoms
The signs and symptoms of infectious mononucleosis vary with age.Children
Before puberty, the disease typically only produces flu-like symptoms, if any at all. When found, symptoms tend to be similar to those of common throat infections.Adolescents and young adults
In adolescence and young adulthood, the disease presents with a characteristic triad:- Fever – usually lasting 14 days; often mild.
- Sore throat – usually severe for 3–5 days, before resolving in the next 7–10 days.
- Swollen glands – mobile; usually located around the back of the neck and sometimes throughout the body.
The most prominent sign of the disease is often pharyngitis, which is frequently accompanied by enlarged tonsils with pus—an exudate similar to that seen in cases of strep throat. In about 50% of cases, small reddish-purple spots called petechiae can be seen on the roof of the mouth. Palatal enanthem can also occur, but is relatively uncommon.
A small minority of people spontaneously present a rash, usually on the arms or trunk, which can be macular or papular. Almost all people given amoxicillin or ampicillin eventually develop a generalized, itchy maculopapular rash, which however does not imply that the person will have adverse reactions to penicillins again in the future. Occasional cases of erythema nodosum and erythema multiforme have been reported. Seizures may also occasionally occur.
Complications
is common in the second and third weeks, although this may not be apparent on physical examination. Rarely, the spleen may rupture. There may also be some enlargement of the liver. Jaundice occurs only occasionally.It generally gets better on its own in people who are otherwise healthy. When caused by EBV, infectious mononucleosis is classified as one of the Epstein–Barr virus–associated lymphoproliferative diseases. Occasionally, the disease may persist and result in a chronic infection. This may develop into systemic EBV-positive T cell lymphoma.
Older adults
Infectious mononucleosis mainly affects younger adults. When older adults do catch the disease, they less often have characteristic signs and symptoms such as the sore throat and lymphadenopathy. Instead, they may primarily experience prolonged fever, fatigue, malaise, and body pains. They are more likely to have liver enlargement and jaundice. People over 40 years of age are more likely to develop serious illness.Incubation period
The exact length of time between infection and symptoms is unclear. A review of the literature made an estimate of 33–49 days. In adolescents and young adults, symptoms are thought to appear around 4–6 weeks after initial infection. Onset is often gradual, though it can be abrupt. The main symptoms may be preceded by 1–2 weeks of fatigue, feeling unwell and body aches.Cause
Epstein–Barr virus
About 90% of cases of infectious mononucleosis are caused by the Epstein–Barr virus, a member of the Herpesviridae family of DNA viruses. It is one of the most commonly found viruses throughout the world. Contrary to common belief, the Epstein–Barr virus is not highly contagious. It can only be contracted through direct contact with an infected person's saliva, such as through kissing or sharing toothbrushes. About 95% of the population has been exposed to this virus by the age of 40, but only 15–20% of teenagers and about 40% of exposed adults develop infectious mononucleosis.Cytomegalovirus
About 5–7% of cases of infectious mononucleosis are caused by human cytomegalovirus, another type of herpes virus. This virus is found in body fluids including saliva, urine, blood, tears, breast milk and genital secretions. A person becomes infected with this virus by direct contact with infected body fluids. Cytomegalovirus is most commonly transmitted through kissing and sexual intercourse. It can also be transferred from an infected mother to her unborn child. This virus is often "silent" because the signs and symptoms cannot be felt by the person infected. However, it can cause life-threatening illness in infants, people with HIV, transplant recipients, and those with weak immune systems. For those with weak immune systems, cytomegalovirus can cause more serious illnesses such as pneumonia and inflammations of the retina, esophagus, liver, large intestine, and brain. Approximately 90% of the human population has been infected with cytomegalovirus by the time they reach adulthood. Most are unaware of the infection. Once a person becomes infected with cytomegalovirus, the virus stays in their body throughout the person's lifetime. During this latent phase, the virus can be detected only in monocytes.Other causes
, a parasitic protozoon, is responsible for less than 1% of the infectious mononucleosis cases. Viral hepatitis, adenovirus, rubella, and herpes simplex viruses have also been reported as rare causes of infectious mononucleosis.Transmission
infection is spread via saliva, and has an incubation period of four to seven weeks. The length of time that an individual remains contagious is unclear. The chances of passing the illness to someone else may be highest during the first six weeks following infection. Some studies indicate that a person can spread the infection for many months, possibly up to a year and a half.Pathophysiology
The virus replicates first within epithelial cells in the pharynx, and later primarily within B cells. The host immune response involves cytotoxic T cells against infected B lymphocytes, resulting in enlarged, reactive lymphocytes.When the infection is acute, heterophile antibodies are produced.
Cytomegalovirus, adenovirus, and Toxoplasma gondii infections can cause symptoms similar to infectious mononucleosis, but a heterophile antibody test will test negative and differentiate those infections from infectious mononucleosis.
Mononucleosis is sometimes accompanied by secondary cold agglutinin disease, an autoimmune disease in which abnormal circulating antibodies directed against red blood cells can lead to a form of autoimmune hemolytic anemia. The cold agglutinin detected is of anti-i specificity.
Diagnosis
The disease is diagnosed based on:Physical examination
The presence of an enlarged spleen, and swollen posterior cervical, axillary, and inguinal lymph nodes are the most useful to suspect a diagnosis of infectious mononucleosis. On the other hand, the absence of swollen cervical lymph nodes and fatigue is the most useful to dismiss the idea of infectious mononucleosis as the correct diagnosis. The insensitivity of the physical examination in detecting an enlarged spleen means it should not be used as evidence against infectious mononucleosis. A physical examination may also show petechiae in the palate.Heterophile antibody test
The heterophile antibody test, also known as the monospot test, works by agglutination of red blood cells from guinea pigs, sheep and horses. This test is specific but not particularly sensitive. Approximately 90% of diagnosed people have heterophile antibodies by week 3, disappearing in under a year. The antibodies involved in the test do not interact with the Epstein–Barr virus or any of its antigens.The monospot test is not recommended for general use by the CDC due to its poor accuracy.