Mononucleosis

Infectious mononucleosis is caused by the Epstein-Barr virus (EBV). It is a double stranded DNA virus indistinguishable from other members of the herpes virus group. It get its' name from the mononuclear (single nucleus) cells. It is also known as the "kissing disease", because the most frequent mode of transmission is intimate salivary contact. It can also be transmitted from shared drinking and eating utensils, toothbrushes, etc. Mono is not likely to spread by aerosol (ex. sneezing) or fomites (ex. doorknobs).

Mononucleosis is a clinical syndrome that can be characterized by a multitude of symptoms. They include headache, fever, sore throat, and lymph adenopathy (swollen and tender lymph nodes). Other symptoms include enlargement of the spleen and liver, fatigue, loss of appetite, periorbital edema (swelling of the tissue around the eyes), petechiae (tiny bruising like spots on the roof of mouth), and a fine rash. The white blood cell and liver enzyme counts are elevated. This disease occurs most often in adolescents and young adults.

It is a disease that is grouped into a class known as a viral infection; more specifically it is caused by the Ebstein-Barr virus (EBV). EBV is a herpes virus. EBV only infects human B-lymphocytes. The virus usually remains dormant, but can be activated using certain chemicals or when subjected to certain bodily conditions.

To understand how this virus affects the body, we must first have a brief overview of the body and it's immune system. The body's defense mechanisms can be split into two groups; non-specific and specific defense mechanisms. Non-specific mechanisms basically are the barriers that keep pathogens from penetrating the body. For example the epithelial membranes that cover the body and the strong acidity of the stomach which kills pathogens before they have the opportunity to infect the system. Specific mechanisms help an individual acquire the ability to defend against specific pathogens by prior exposure to these pathogens.

B-lymphocytes are the ones that are affected directly upon when the body is subjected to this type of infection. Their role in the body is vital for immunity. They are grouped into five subclasses, depending upon some of the polypeptides in their makeup. The basic role of B-lymphocytes is to secrete antibodies that they have made due to them coming into contact with an antigen. Each B-lymphocyte has two sites where specific antigens can combine, and this binding is what promotes the body's reaction to the infection. The B-lymphocyte is involved in what is called humoral immunity. This is when the cell secretes the antibodies but doesn't do the job directly.

T-lymphocytes (T-cells) are the cells that actually do the fighting of the infections themselves. There are three classes of T-cells.

The first is called a Cytolytic T cell (killer T-cell). The way that these cells work is that they have an antigen presented to them or they have found a rogue tissue cell. The way they can tell is by the protein vehicle that is left on the outside of the cell from when the virus entered it. This is very important later on with regards to mononucleosis. It then injects a toxin called lymphotoxin and this kills the cells from the inside out. Another way that it can kill is by using another protein called perforin. It diffuses to the infected cell and inserts itself into the membrane and forms a pore, which causes there to be a hole in the membrane and unbalances the sodium and potassium concentration gradient. This kills the cell before the virus can be made completely.

The second and third types of T-cells are ones that are called Helper T-lymphocytes and Suppressor T-lymphocytes. Helper T-cells are ones that stimulate the functions of B and Killer T-lymphocytes. Suppressor T-cells suppress this function as their name suggests.

EBV first infects the epithelium of the mouth normally and then spreads to the sub epithelial circulating B-lymphocytes. The effect on the target B-cells is instead of dying at the end of a normal life span, the infected cells live on to replicate and produce a variety of antibodies, including antibodies to the virus itself, but also nonfunctioning antibodies called heterophils. Changes to the infected B-cells cause them to resemble monocytes: an entirely different type of white blood cell. It is there resemblance to the monocytes that led to the name Mononucleosis. Tonsils, regional and systemic lymph nodes enlarge because of the virus infected B-lymphocytes. Similar changes also occur in the spleen.

The usual mode of transmission for the EBV infection is by direct contact with the saliva of a previously infected person with the saliva of a non-infected person. This virus is fragile outside the human host. Infection during infancy is usually due to contact with the food of an infected