The Epstein-Barr Virus (EBV), also known as human herpesvirus 4, is a common and widespread member of the herpes family of viruses. Most people contract it at some point during their lifetime. EBV establishes a permanent infection in the body, but for the majority of infected individuals, it remains largely unnoticed.
Primary Infection The Acute Phase
The initial stage of infection begins when the virus enters the body, typically through the transfer of saliva. EBV first targets the epithelial cells in the mouth and throat, where it can undergo lytic replication to produce new viral particles. From the epithelial cells, the virus spreads to B-lymphocytes, a type of white blood cell, which then carry the infection throughout the body.
The acute phase often manifests as Infectious Mononucleosis, particularly when infection occurs during adolescence or adulthood. Symptoms include fatigue, fever, a sore throat, and swollen lymph nodes in the neck. The symptomatic period usually lasts two to four weeks, though fatigue can sometimes persist for several months. Young children infected with EBV usually experience mild or no noticeable symptoms, making the infection subclinical.
Establishing Latency
Following the acute phase, the virus transitions into latency, establishing a permanent presence primarily within the memory B-lymphocytes. The virus’s linear DNA genome circularizes to form an episome that resides in the cell nucleus. This episome is copied by the host cell’s machinery as the cell divides.
To evade detection by the immune system, the virus minimizes its gene expression, only expressing a limited subset of viral genes. This minimal expression allows the infected B cells to survive and proliferate without alerting the immune system. This dormant state is characterized by the absence of symptoms and the virus remaining tightly controlled by immune surveillance.
Viral Reactivation
The periodic reawakening of the dormant virus is known as lytic reactivation. While the virus remains latent for life, it can occasionally switch back to its lytic cycle. This switch is often triggered by factors such as physiological stress, a weakened immune system, or co-infection with other pathogens.
During reactivation, the virus replicates in the B cells and epithelial cells of the throat, producing infectious viral particles. These viruses are then shed into the saliva, allowing for transmission to new hosts. A person undergoing viral shedding is frequently asymptomatic, meaning they can spread the virus without being aware they are infectious.
Long Term Health Consequences
Even after latency is established, the virus can have lasting implications. While most individuals remain healthy, the latent virus is associated with an increased risk of developing specific, rare long-term health issues. This connection stems from the virus’s ability to promote the survival and proliferation of the B cells it infects.
EBV is classified as an oncogenic virus and is linked to certain cancers, including Burkitt lymphoma, Hodgkin lymphoma, and Nasopharyngeal carcinoma. The virus has also been implicated in the development of several autoimmune conditions. Studies have shown a connection between past EBV infection and an increased risk of developing Multiple Sclerosis (MS) and Systemic Lupus Erythematosus.