Mono The Disease

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What is the cause of Infectious Mononucleosis?

• Infectious Mononucleosis is caused by the Epstein-Barr Virus³. Therefore, Infectious Mononucleosis (IM) is caused by a viral infection. Epstein-Barr virus is the cause of the variety of symptoms, which together are classified as Infectious Mononucleosis. The symptoms of Infectious Mononucleosis (IM) can also be called Glandular Fever². IM received this alternate name because of some of the symptoms involved. Swelling of the lymph nodes in the neck and cervical area as well as a persisting fever are two symptoms which lead to the name “glandular.”² The connection between Epstein-Barr virus (EBV) causing the symptoms known as Infectious Mononucleosis (IM) was made in 1968 by Werner Henle¹. Humans are currently the only known carrier of the EBV1. So far, EBV is not found to be a cross species virus.
• Epstein-Barr virus is very common and infects 90% of all people. In the United States by the time children are five years of age 50% have been infected by (EBV)¹. Out of this large percentage of people infected with EBV, not all of them will show signs or symptoms. People who are healthy and people who are sick can carry and spread EBV.
• People with Infectious Mononucleosis are able to spread the active form of EBV for a number of weeks after they don't have any apparent symptoms¹. Typically if individuals express the symptoms of IM from a number of weeks to two months it will be considered acute EBV¹. If individuals have symptoms for more than six months, it is most often going to be classified as a chronic EBV infection. In the case of chronic EBV, the virus might not be in its fully active form but still present in the cells of the infected individual¹.
• The EBV infects the B lymphocytes located in the oropharynx region². The virus is able to spread to other parts of the body. This viral spread is indicated by the wide range of symptoms of IM. The infected B cells can travel through the liver, spleen and lymph nodes². Swelling is a symptom and is observed in each of these tissues when the individual is infected with the active form of EBV2.

What is Epstein-Barr Virus?

• Each EBV contains a DNA strand with information to make more viruses once the virus has entered into the body cells. There are sequence variations in the genes which have been found to differ depending on the location in the world. The specific gene sequences which differ include; LMP-1, EBNA-1 and B2LF-1⁴. EBV as a structure is a double stranded genome⁴. There are approximately 170 kilo bases. These kilo bases are responsible for encoding more than 85 genes⁴. There are two known strains of EBV; EBV-1 and EBV-2⁴. Both of the viruses can cause symptoms of Infectious Mononucleosis (IM). The symptoms caused by the two strains cause very similar symptoms.
• EBV is part of the human herpes virus classification. Specifically, EBV is classified under human herpes virus category four, classified as a gamma herpes virus⁴.

All of the herpes viruses have features in common. Some of these features include; an ability to establish latency during primary infection⁴. This means that the virus may not affect the individual right away. The virus could remain dormant or latent for weeks, or even months. There are specific triggers in the individuals body or the environment which could cause the virus to become active⁴. Another common feature of the gamma herpes viruses is permanent residency the virus takes in the host organism⁴. The EBV will be in the individual’s body for the rest of their life.EBV remains as a circular episomal DNA segment residing in memory B cells⁴. EBV can also remain in epithelial cells. EBV will undergo episodic lytic replication if there is a reoccurrence of the virus in the host⁴.

• EBV directly targets B lymphocytes, also called B cells⁴. B lymphocytes are a type of white blood cell. B lymphocytes are a type of immune cell⁵. B lymphocytes are responsible for making antibodies, which are specific kinds of proteins. Antibodies have a critical role in fighting infection, therefore attributing a crucial role in fighting infections to the B cells which produce the antibodies⁵.

Infection caused by Epstein-Barr Virus

• EBV is commonly transmitted through the saliva³. This means the virus is able infect the salivary glands producing saliva.
• EBV spreads and replicates into the oropharyngeal lymphoid tissues. When the virus enters the lymph tissues, the circulation of the virus around the body becomes possible³. The other lymph system structures affected by the transmission of EBV in the lymph tissues are the liver, spleen and B lymphocytes in the peripheral blood³.
• Viral infections are able to spread throughout the body by the means of cell lysis³. After the virus has reproduced, it can travel throughout the host organism. It will affect nearby structures. These affected structures allow for further viral replication to take place³. The Epstein-Barr virus becomes a part of the cells located in the oropharyngeal airway³. This is the pathway that the air will take to get into your lungs through your mouth or your nose. Once the virus has established itself, the virus is able to grow and reproduce by using the individuals own body cells. The virus will insert its own DNA into the host cell. This causes the nasopharyngeal epithelial cells to become EBV cells able to produce more EBV cells³. When individuals are in the latent stage of the infection, the epithelial cells are the primary location of the virus³. Due to the location of the latent form of EBV, they are still in prime location to become in contact with the rest of the body. The EBV latent cells are able to infect the B cells as they pass through their circulation in the oropharyn³.

Who does Epstein-Barr Virus infect?

• The effects of EBV causing symptoms of IM most commonly affect adolescents and young adults. The most common age affected is between the ages of 15 and 25 years old⁶. The reason for this age group being affected is a result of more “acceptable host cells” for the virus to infect. Another reason for adolescence being a target age range for the EBV virus could be due to exposure. If an individual in their adolescence was not exposed to EBV as a child, when exposed as a young adult the resulting symptoms of IM will have a more severe effect on the body and immune system⁶.
• If a younger child becomes infected with EBV, the symptoms are usually just passed off as a cold⁶. IM has been reported to be one of the top causes of prolonged illness in adolescents⁶. There are between 5% and 10% of University students who become infected and show symptoms of IM every year⁶.

During the Infection

• It can take from four to six weeks for the symptoms of IM to show up and become apparent AFTER being infected with the EBV⁷. There are different stages of the EBV infection. These include; primary acute, convalescent, latent and reactivation infection⁷.
• People who are infected by the EBV virus and show symptoms for mono are contagious for four to six weeks plus. In addition, people can spread the virus even though it may be latent in the body for up to five months⁷.
• It is important to know the structure of the EBV virus in order to make an accurate diagnosis during testing. The structure of the EBV virus can change throughout the different infection stages. When the individual is in the latent stage of the infection, the genes expressed by the EBV change compared to the active form of the EBV⁷. These changes are expressed through different proteins⁸. A restricted set of genes is expressed in the latent form instead of the full set which would be expressed when the individual is in the infection stage⁷. These protein difference are used to diagnose whether the patient has primary acute, convalescent, latent or reactivation EBV infection⁸. Most often the EBV will be found in the epithelial cells⁸. The mature virus particles are going to be found in the cytoplasm of the epithelial cells.
• All viruses posses similar structural features. If the virus is mature, it will have a nucleoid, capsid and an envelope⁸. Double stranded DNA is going to be found in the nucleoid of the virus⁸. The DNA is specific to each different kind of virus. The specific DNA will be able to infect host cells and cause them to begin to use the viral DNA to create more viral DNA. The envelope is responsible for containing proteins that are specific to the virus. These proteins will also infect the host cell and instruct it to replicate the virus⁸.

Biochemical Interaction between EBV and the Host

• IM can be classified under a grouping of diseases called immunopathological diseases⁶. There has been a correlation developed between IM symptoms, T cell activation and B cells numbers. The level of T cell activation relates to the number of B cells that are infected with the EBV⁶. The B cells are circulating in the blood, therefore the infected B cells are also circulating in the blood. The number of infected B cells determines what is called the virus load⁶. The heavier or greater the viral load, the greater or more severe the symptoms are. If the individual is exposed to a large dose of the EBV, they would have a higher viral load early in the infection period. This would lead to a high number of T cells becoming activated⁶.
• EBV attaches to the host via a glycoprotein (gp350/220)9. This glycoprotein is located on the outer envelope. The B lymphocyte (which is the target for the EBV virus) has a receptor called CD21 which is specific for the EBV. The virus is then able to enter the host cell. Fusion occurs between the viral envelope and the host B cell vesicle membrane. The nucleocapsid is responsible for carrying the DNA of the virus⁹. This is able to now enter and travel into the nucleus of the host cell or host B cell. The DNA genome is released into the host cell. The DNA is able to form a circular shape which is known as an episome⁹. After the formation of the episome, the virus can choose a pathway for host cell infection. As demonstrated with the symptoms of IM, the virus can choose to infect with a lytic release of the virus or a latent infection⁹. A lytic infection of EBV can be found in the saliva of a person who has been infected. The infected individual can express the lytic infection of EBV for the first 12-18 months⁹. This is a long time for the virus to be present in the lytic infectious state. This means that the virus is still present in the oral epithelial cells for that duration of time. An individual who has a latent EBV infection can have EBV found in 20-30% of their saliva⁹.
• One speculation for the increase in cases of IM in adolescents compared to children could be related to SAP. SAP is known as SLAM-Activating-Protein; SLAM stands for Signaling Lymphocyte Activation Molecule⁶. SLAM is a Tran membrane protein. Its importance and connection with EBV is because it is located on the membranes of B and T cells⁶. SAP is found to be a defect in individual which can cause X-Linked Lymphoproliferative Syndrome. This is a syndrome which is associated with a higher mortality rate with the infection of EBV and further development of IM⁶. It is suggested that children might express more SAP than adolescents⁶. This would allow children to have a tighter control on the EBV, allowing it to not infect as many cells. If children have a higher expression of a protein able to signal their lymphocytes, this should allow for faster reaction time and elimination of viruses and toxins.
• The Epstein-Barr virus causes a response of antigen driven expansions of specifically CD8 T lymphocytes. These CD8 lymphocytes make up more than half of the circulating types and numbers of lymphocytes⁶. These lymphocytes release cytokines which can be of two different types including TH1 type and interleukin. These two types of cytokines have been identified in creating the symptoms of IM⁶. Therefore the EBV acts to increase cytokines which work throughout the body to create symptoms such as fever through a number of enzymatic pathways and cascades.

B cell lymphocytes

• A study by Seung et al. examined the structure and characteristics of B cells. B cells are the cells that are most effected during the course of the Epstein-Barr virus and through the resulting symptoms of Infectious Mononucleosis¹⁰. In the Seung study there were results to support that the B lymph cells located in the oropharynx cervical region behave differently than the B cells located in other parts of the body¹⁰. The difference found between the B cell lymph nodes in the cervical region compared to the rest of the body was the secretion of immunoglobin. Cervical lymph nodes did not spontaneously secrete immunoglobin¹⁰.
• Immunoglobin is responsible for neutralizing infectious viruses¹⁰. In the case of IM, the B cells would and should secrete immunoglobin in order to try and control and neutralize the EBV. Without the expression of immunoglobin, the cervical lymph nodes did not express certain enzymes which were responsible for controlling B cell differentiation¹⁰. The expression of immunoglobin can also be attributed to effects from the EBV. When the virus enters the body an antigen will bind to a receptor on the B cells. The signal generated from this binding of the EBV to the B cell determines whether the B cells will begin to secrete immunoglobin or not¹⁰.
• The goal of a virus would be to infect host cells and allow for the production and replication of more viral cells. EBV is most commonly found in the oropharyngeal region¹⁰. This would mean that the EBV is able to travel only a short distance to reach the cervical lymph nodes. If the virus has a goal of reproduction, it would not want to allow the cells to secrete immunoglobin which would have a negative effect on viral reproduction. Therefore, through EBV inhibiting immunoglobin in the cervical lymph nodes, this allows for the EBV to be replicated in this region.

During an infection, the cervical lymph nodes experience a high degree of activity¹⁰. These lymph nodes drain a large volume of fluid and waste tissue particles. Due to the location of the cervical lymph nodes, there are many other important structures located including veins and arteries in this area. Due to the constant stimulation from different antigens, it was proposed in this research that perhaps the cervical lymph node cell would be more responsive. This was not the case found in the research. The B cells located in the cervical region behaved with similar responses to other B cells in the body with no enhanced capabilities¹⁰.

Symptoms

Symptoms can start to appear up to four to six weeks after the initial infection of EBV¹¹. Individuals who are infected with EBV could have some or all of these symptoms. It is also possible to have minor symptoms and not become very affected by them. Due to the range of symptoms, it is possible that the collection of symptoms known as IM might be misdiagnosed as another infection; such as strep throat or the flu¹¹.

A) swollen glands (sides and back of neck, under arms, above groin).
B) fever
C) fatigue
D) sore throat
E) loss of appetite
F) abdominal pain
G) enlargement of the spleen
H) liver swelling
I) nausea, vomiting, upset stomach
J) rash

How the EBV works to create these symptoms

• B) Fever - Once the virus has entered a host cell, it creates proteins. These proteins work to create a new capsid for the virus². The proteins become the targets for protein degradation. The body produces and proceeds with a cascade of events in order to try and eliminate and contain the infection. The body increases the cascade of events in affected target areas such as the lymph nodes². A mediator enzyme is produced nearing the end of this cascade called interleukin-1. This continues on to further steps which results in the release of prostaglandin². Prostaglandin is an enzyme which raises the thermoregulatory set point of the body. This means that the temperature set point has been raised and the internal and external temperature of the body is temporarily allowed to be increased². The fever is a result of the cascade of events resulting from the initial attempt to control and contain the virus². When the virus has been eliminated and controlled, the cascade of events will begin to be down-regulated. This will lead to a smaller production of prostaglandins leading to a lowered thermoregulatory body temperature.
• F) Abdominal pain - this type of pain needs to be taken seriously. It could be indicative of having an enlarged spleen. Extra care needs to be taken in order to avoid damaging your spleen or liver.
• G) enlarged spleen - Contact sports need to be avoided as well as any heavy lifting. The spleen is an immune organ¹². The spleen and the lymph nodes and glands are both immune system components. This means that both will enlarge in order to increase their performance¹². The spleen will swell and increase in size in order to try and cleanse the body. In the case of EBV the spleen is swelling in order to try and rid the body of the virus. The spleen is also enlarging to remove the toxins being produced as by products in various reactions throughout the body¹². One of its responsibilities is to break down red blood cells¹². If red blood cells aren’t broken down, anemia can result. When the sympathetic nervous system is activated, it causes an activation of the spleen12. The spleen and the vessels contract when stimulated. The contraction causes the release of stored red blood cells¹². This will allows the body to utilize the red blood cells to increase the carrying capacity of haemoglobin in the blood. This will allows muscles and target tissues to get more oxygen faster. There are some specific types of cells in the spleen called reticuloendothelial cells¹². These cells are responsible for removing debris, bacteria and parasites.
• J) rash - A rash is most commonly associated with reactions to antibiotics⁹. IM is caused by a virus; therefore antibiotics would not target the virus. Antibiotics may have been given to an individual because the symptoms were predicted to be caused by strep throat not IM⁹.

Further Symptoms and Complications

• The symptoms of IM rarely result in fatalities. Occasionally a ruptured spleen could occur as a complication of IM, leading to death¹³.
• Host cells can be infected either lytically or latently. Different cell proteins are expressed during each of these types of infection. Latent infections can come in different types⁹. Type one latency has been shown to be associated with Burkitt's lymphoma⁹. In type one latency, virus encoded RNA's can be found from the EBV virus. Different types of antigens associated with the nucleus can also be assoicated with EBV and linked specifically to Burkitt's lymphoma⁹. Type two latency has been shown to be associated with nasopharyngeal carcinoma⁹. There are a variety of membrane proteins that are specific to type two latency, including; LMP1, LMP2B plus EBER's and EBNA1⁹. Type three latency is the type that is specifically found in healthy individuals⁹.

Burkitt’s Lymphoma and Nasopharyngeal Carcinoma

• Two types of cancer occur in a small number of EBV carriers; Burkitt’s Lymphoma and nasopharyngeal carcinoma¹³. EBV has also been classified as a human tumour virus. These tumours are associated with tumours that can be found in patients that have Burkitt’s lymphoma and nasopharyngeal carcinoma¹³. There a three forms of Burkitt’s lymphoma (BL); endemic (African), sporadic (non-endemic) and the immunodeficiency associated form. In Africa, most of the BL cells also carry the EBV, which is not true in the United States¹³.

Biochemistry of EBV in Burkitt’s Lymphoma

• Below describes the changes that take place at the chemical and molecular level in Burkitt’s Lymphoma (BL) cells. Some of the cells described are BL cells in combination with EBV in the same cell. Some of the cells examined are infected with BL but do not have EBV¹⁴.
• Mutations or over expression of the p53 negative regulator (MDM2) could cause p53 inactivation observed in BL cells. Reactivation of the p53 in these EBV - BL cells can be caused by decreasing the amount of MDM2¹⁴. This has been shown to lead to nutlin-3 inducing apoptosis. Nutlin-3 is an antagonist to MDM2 leading to the reactivation of p53 in all of the BL cells¹⁴. The level of apoptosis caused by nutlin-3 was responsible for the level of activation induced in the p53. The EBV status of the cell dictated the amount of responsiveness to the change in p53¹⁴. Cells which were classified as being a latency III type as well as being positive for EBV were more resistant to the change back to activation of p53¹⁴. Latency I EBV and BL cells were more sensitive due to nutlin-3¹⁴.

Chronic Fatigue Syndrome

• Chronic Fatigue syndrome (CFS) is a condition which can occur as a result of the EBV leading to symptoms of IM¹⁵. Individuals with CFS feel extreme tiredness all of the time. IM and CSF have some similar symptoms and can be misdiagnosed initially¹⁵. CFS is also linked strongly to viral infections, which is the reason behind the symptoms classified occasionally as IM¹⁵. Immunological dysfunctions are a common to be a side effect of CSF chronic IM. In a study by Katz et al., (2009) it was reported that the chance of adults developing Chronic Fatigue Syndome (CFS) after infectious mononucleosis (IM) was nine to twelve percent¹⁵. It was found that IM is a predictor for CFS, but most of the individuals recovered over time from both conditions. The percentages of individuals developing CFS decreased over time. As the number of months increased after having symptoms of IM; the percentage of people developing CFS decreased. Developing CFS after six months of having IM was thirteen percent compared to four percent developing CFS after twelve months of experiencing symptoms of IM¹⁵.

Immunodeficiencies

• For individuals with primary Immunodeficiencies, EBV can be much more serious. X- linked chromosome syndromes have been identified as Immunodeficiencies with serious complications resulting from an EBV infection⁷. In X-linked chromosome syndromes, the genetic code is different from normal. This allows for EBV genes to more strongly influence the behaviour and activity of infected cells⁷. EBV could lead to cases where symptoms of IM become fatal. EBV in X-linked chromosome syndromes could also lead to infected B cells lymphocytes becoming malignant⁷.
• The inherited X-linked lymphoproliferative syndrome increases the risk of fatality resulting from IM6. In this X-linked condition, the individuals are missing a surface lymphocyte activation marker associated protein (SAP)⁶. This protein serves a regulatory purpose and is activated through signals on the cell surface. With a missing SAP, the level of control of immune activation was not present or not as efficient. Therefore individuals with X-linked lymphroproliferative syndrome can not control the EBV infection⁶.

How to test

• The symptoms of Infectious Mononucleosis (IM) can be very similar to a common cold. Therefore, a blood test is needed to confirm that an individual has IM. The blood test is used to check for an elevated white blood cell count and an elevated number of atypical white blood cells¹⁶.
• A Mono Spot Test is used to confirm the diagnosis of IM. An individual who has a positive reaction to this test will be confirmed as having IM¹⁶. A Mono Spot Test could also be known as; infectious mononucleosis slide test, heterophil antibody test, heterphile antibody test or heterphil agglutination tube test¹⁶. During some of these blood testing methods, there is a possibility for a false positive. The chances of the results being false positive are greater earlier in the course of IM. The number of antibodies have not accumulated to their peak levels at early in the infection. The best time to get tested in order to yield the most correct diagnosis would be between weeks two and five weeks¹⁶. The number of antibodies are normally at their peak around this stage of the EBV infection.
• A primary infection from EBV can be identified for specifically if the Immunoglobin M (IgM) antidoby is present¹⁶. IgM is the antibody for the viral capsid antigen associated with the antibody for the EBV nuclear antigen. A rise in IgM might be indicative of a primary infection of EBV¹⁶One of the most specific and accurate tests for IM are the tests specifically designed to identify antibodies of the Epstein-Barr virus. These tests identify specifically if the Epstein-Barr viral capsid antigen or Epstein-Barr nuclear antigen are present¹⁶. The negative aspect of this is it is more expensive than the other slightly tests for IM, however it is much more accurate. Tests which are used to identify the heterophile antibodies are not as accurate. The tests for the specific Epstein-Barr viral capsid antigen and nuclear antigen are more accurate for the diagnosis of IM in the earlier stages in children and adults compared to the heterophile antibody test¹⁶.

What does a blood test show?

• Blood tests help the doctors determine if there are any levels of substances that might fall outside of the normal range. The normal range is dictated by your age, gender, race, sex and other factors¹⁶. Blood cell count is one element of the blood work tests. This element is specifically important in IM because the diagnosis is based on identifying an increased number or abnormal white blood cells. A blood test will also look at red blood cells, platelets, hemoglobin, hemotocrit and mean corpuscular volume. Blood glucose levels are also indicated which could be a predictor for diabetes. Cholesterol can be broken down into total cholesterol, LDL and HDL cholesterol¹⁶.
• The chemical component of the blood work is also important. Sodium, potassium and chloride are important electrolytes in the body. Albumin is one of the proteins in the blood, as well as globulins which are a mixture of proteins and immunoglobulin or antibodies. Iron is also monitored and can be a cause of anemia. Anemia can also be a result of problems in spleen function¹⁶. Therefore iron levels should be examined closely in order to look for links of associated symptoms.

Epidemiology

EBV is said to be “ubiquitous,” which means to be or seems to be everywhere at once, constantly encountered⁴. EBV is said to be etiologically linked to nasopharyngeal carcinoma. Nasopharyngeal carcinoma is an endemic which has affected Southern China most heavily⁴. EBV has also been found to be etiologically linked to Burkitt’s lymphoma, which is an endemic to regions of equatorial Africa⁴.

Ubiquitous - seems to be everywhere at once, constantly encountered
Etiology - the study of causes or origins
Endemic - is a disease that is always present to some degree in a certain class of people, who are living in a particular location⁴.