The final in our three-part series about infectious diseases, this one's about the Epstein-Barr virus, the pathogen that causes, among other things, mononucleosis. Enjoy.
The Epstein-Barr Virus (EBV) is endemic to the human population and is prevalent over the entire earth; it has been demonstrated that up to 95% of adults (aged 35-40) have shown serological response to the virus indicating exposure to infection. EBV is a member of the herpes family, and like other herpes viruses, it is an enveloped polyhedral capsid containing a linear double strand of DNA that can encode for up to 200 genes. Glycoproteins on the envelope are responsible for the fusion between the envelope and the host cell membrane.
The virus enters the body through the epithelial cells of the mouth and throat, and it is transmitted through the saliva of infected individuals. This route of infection has earned the virus the nickname “the kissing disease,” especially since infection via the blood or air is not known to occur. Although the virus, while infecting these epithelial cells, multiplies by the lytic cycle, lysis does not occur because active virions leave the host cell via budding, not bursting. From the epithelial cells, the virus infects the B lymph cells of the immune system and causes a latent infection as an episome, employing the lysogenic cycle. Once the disease reaches this stage in healthy individuals, they will have autoimmunity, and the relapse of symptoms is unlikely, however, the reactivation and shedding of new virions without symptoms is possible. It is these otherwise healthy individuals who shed the active virions are the reservoir for this virus and the reason that this virus is impossible to eradicate. There is no vaccine available for this virus.
In immune compromised individual such as AIDS patients or those undergoing immune suppressing chemotherapy, EBV is known to cause very rare and specific forms of cancer. Burkitt lymphoma, a malignancy of the lymphocyte is one such cancer. It was studying this form of cancer in children from tropical Africa that Anthony Epstein and Yvonne Barr discovered this virus. It was Dennis Burkitt who posited that the lymphoma might have an infectious causative agent. Another complication is nasopharygeal carcinoma, a cancer of the epithelial cells in the mouth and throat. AIDS patients specifically see “hairy tongue” leukoplakia, which develops a white plaque on the tongue.
EBV expresses symptoms in a variety of different ways, depending on many factors, including co-infection, immunodeficiency, genetic predisposition, and even socio-economics and age of infection. Many people are infected during their childhood years, and the disease at this age results in non-specific symptoms that are often confused with other childhood diseases such as cold or flu. Infection during adolescence cause a more severe form of the disease called mononucleosis or mono, symptoms of which are extended malaise, sore throat, fever, muscle ache, swollen lymph glands and exudates on the tonsils. These symptoms and the age of the patient are the primary tools for diagnosis, however lab tests must be done to verify EBV infection. The illness caused by EBV usually does not last more than four months. If the illness lasts longer than six months further tests may be needed to diagnose the illness as Chronic Fatigue Syndrome. Studies have shown a correlation between EBV and Chronic Fatigue Syndrome, however, it has not been demonstrated that EBV is the causative agent. It is thought that EBV is probably a co-factor in the onset of CSF and other environmental and genetic factors probably play a role.
The Epstein-Barr Virus (EBV) is endemic to the human population and is prevalent over the entire earth; it has been demonstrated that up to 95% of adults (aged 35-40) have shown serological response to the virus indicating exposure to infection. EBV is a member of the herpes family, and like other herpes viruses, it is an enveloped polyhedral capsid containing a linear double strand of DNA that can encode for up to 200 genes. Glycoproteins on the envelope are responsible for the fusion between the envelope and the host cell membrane.
The virus enters the body through the epithelial cells of the mouth and throat, and it is transmitted through the saliva of infected individuals. This route of infection has earned the virus the nickname “the kissing disease,” especially since infection via the blood or air is not known to occur. Although the virus, while infecting these epithelial cells, multiplies by the lytic cycle, lysis does not occur because active virions leave the host cell via budding, not bursting. From the epithelial cells, the virus infects the B lymph cells of the immune system and causes a latent infection as an episome, employing the lysogenic cycle. Once the disease reaches this stage in healthy individuals, they will have autoimmunity, and the relapse of symptoms is unlikely, however, the reactivation and shedding of new virions without symptoms is possible. It is these otherwise healthy individuals who shed the active virions are the reservoir for this virus and the reason that this virus is impossible to eradicate. There is no vaccine available for this virus.
In immune compromised individual such as AIDS patients or those undergoing immune suppressing chemotherapy, EBV is known to cause very rare and specific forms of cancer. Burkitt lymphoma, a malignancy of the lymphocyte is one such cancer. It was studying this form of cancer in children from tropical Africa that Anthony Epstein and Yvonne Barr discovered this virus. It was Dennis Burkitt who posited that the lymphoma might have an infectious causative agent. Another complication is nasopharygeal carcinoma, a cancer of the epithelial cells in the mouth and throat. AIDS patients specifically see “hairy tongue” leukoplakia, which develops a white plaque on the tongue.
EBV expresses symptoms in a variety of different ways, depending on many factors, including co-infection, immunodeficiency, genetic predisposition, and even socio-economics and age of infection. Many people are infected during their childhood years, and the disease at this age results in non-specific symptoms that are often confused with other childhood diseases such as cold or flu. Infection during adolescence cause a more severe form of the disease called mononucleosis or mono, symptoms of which are extended malaise, sore throat, fever, muscle ache, swollen lymph glands and exudates on the tonsils. These symptoms and the age of the patient are the primary tools for diagnosis, however lab tests must be done to verify EBV infection. The illness caused by EBV usually does not last more than four months. If the illness lasts longer than six months further tests may be needed to diagnose the illness as Chronic Fatigue Syndrome. Studies have shown a correlation between EBV and Chronic Fatigue Syndrome, however, it has not been demonstrated that EBV is the causative agent. It is thought that EBV is probably a co-factor in the onset of CSF and other environmental and genetic factors probably play a role.
