Mononucleosis
By Dave Penn
Summer Discovery Program: Exploring Careers in Medicine
Instructor: Steve Anisman
Summer, 1998
The Kissing Disease
Mononucleosis is a DNA viral disease that occurs mostly in adolescents and young adults. Nicknamed "mono," or the "kissing disease," it has many symptoms that contribute to making a person very sick. The most common symptoms are fever, sore throat, swollen lymph nodes, and fatigue. It is contracted mainly through the exchange of saliva which is why it has earned its nickname. In the United States, there are about 100,000 cases of mono a year.
The disease was first noticed in the 1880's by the Germans. It occurred mainly in children and then spread throughout the rest of the family. The German doctors called this illness "glandular fever." Today, scientists have realized that the doctors from Germany were describing a disease slightly different from mono, and consider glandular fever a symptom of mononucleosis. The patients described by the Germans were between the ages of five and eight, which was not the usual age group to get mono.
In 1920, Dr. Thomas P. Sprunt and Dr. Frank A. Evans examined blood from patients suspected of having mono. They found that the number of mononuclear lymphocytes was significantly larger than in uninfected individuals, and the lymphocytes looked unusual. The cells themselves and the nucleus of these cells were larger than normal. A mononuclear lymphocyte is a type of disease fighting white blood cell. The increase in mononuclear cells is what gave mononucleosis its name.
Other diseases, such as leukemia, also have mononuclear cells. The beginning of leukemia is very similar to mononucleosis. Doctors were having trouble distinguishing between the two until symptoms became more pronounced. Drs. Sprunt and Evans distinguished between the two by stating that mono has similar mononuclear cells and leukemia has a variety of different looking cells.
In 1932, Rodman Paul and Walls Bunnell, two American scientists, found that human blood with mono forms mono clumps (clumps of red blood cells) when mixed with sheep blood. This allowed scientists to help diagnose mono more accurately, thus ruling out other diseases.
Mononucleosis received the name "kissing disease" from the chief physician at the U.S. Military Academy at West Point. He noticed how cadets became sick over Christmas vacation when they went to see their girlfriends.
It was not until 1967 that the cause of mononucleosis was determined. Ninety percent of the time, mononucleosis is caused by the Epstein-Barr Virus(EBV). This virus is a member of the herpes family. Also in the family are certain cancers, genital herpes, cold sores, chicken pox, and birth defects. Mono can also be caused by cytomegalovirus, another virus in the herpes family. Herpesviruses are always permanent. Once it is in you, it can remain latent for long periods of time.
Mononucleosis is diagnosed through blood tests. A Complete Blood Count (CBC) shows the increase of white blood cells, and an increased percentage of lymphocytes which also look abnormal. The Monospot, or heterophile, antibody test mixes the patient's blood with the red blood cells of sheep. If the cells clump, a positive indication of mono exists. Because mononucleosis can resemble other diseases, these tests can rule out hepatitis, strep throat, leukemia and other cancers, meningitis, appendicitis, measles, and others.
The highest percentage of people who get mono are teenagers and college students, but more males than females get mono. Most people become infected with EBV during childhood, but this doesn't mean they will get mononucleosis. The presence of EBV allows us to build up antibodies to help protect ourselves from mono.
Mono is most common during the spring and fall. Most likely it occurs in the fall because young people are in more contact with other young adults because of the return to school. It can also occur a lot in times of stress, such as during finals or graduation, when the immune system is weakened. Mono doesn't occur in epidemics, but clusters of cases do occur.
Mononucleosis is not a particularly easy disease to contract. It is passed through direct contact with infected saliva. The most common way teens contract mono is through kissing, but this isn't the only way teens can get it. Drinking out of the same glass and sharing silverware or a toothbrush can also give you mono. Another way to get it is through a blood transfusion. Doctors say that the symptoms rarely develop under this condition. Mono can be passed along even six months after a person has lost the symptoms, but those getting over mono are not always the people responsible for passing the disease along. EBV can become active in a person who previously had it and then passed on to another person. A person can only be infected with the virus if he or she has never been exposed to it.
Mononucleosis mainly affects the lymphatic system. The first thing that happens is the virus starts reproducing inside the throat. The new viruses are carried by the lymph system to special tissue with lymphocytes, a type of white blood cell. The EBV then infects lymphocytes called B cells, causing them to change or mutate and reproduce out of control. When other lymphocytes, called T cells, detect the infected B cells they kill them. This is what causes the person to get sick, the body fighting its own cells. As this goes on, the lymph nodes get swollen. The B cells, while infected, let out an antibody that indicates that mono is present.
When the killer T cells have killed enough of the virus to cure the body, they rest and almost call a truce with the virus. However, they still search the body for more infected cells.
People with mono rarely experience a recurrence of the illness. But, since EBV stays in the body for one's lifetime, a person with relapses of the disease generally has a faulty immune system.
Young children and older adults who get mono exhibit few symptoms and the disease often goes undiagnosed. Teenagers develop symptoms two to seven weeks after exposure. Initial symptoms are a general malaise: headache, fatigue, no appetite, chills, puffy eyelids. This is followed by severe sore throat, fever, general aches, and swollen lymph nodes. Excessive sweating and sensitivity to bright lights may occur. These symptoms usually last for one to three weeks.
Since EBV is involved in other, more serious diseases, scientists have been investigating a vaccine. Dr. Michael Epstein, co-discoverer of the virus, is working on a vaccine that would produce sufficient antibodies to cause an immune response. Tests on humans have not started yet.
Scientists agree that a vaccine to prevent EBV cancer related diseases found in poorer nations is a good idea. They are in doubt whether it should be given to everyone in the U.S. to prevent mono because, perhaps, the body's natural antibodies help prevent other diseases. Introducing a vaccine might tamper with other health functions.