AssessmentsEpstein-Barr virus (Infectious mononucleosis)
Epstein-Barr virus (Infectious mononucleosis)
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 38-year-old woman is brought to the emergency department after developing confusion and lethargy. The patient’s friend reports that she complained of right-sided weakness several days ago. The patient has a history of HIV and is inconsistent with her antiretroviral medication regimen. Temperature is 37.5°C (99.5°F), pulse is 90/min, respirations are 16/min, and blood pressure is 124/82 mm Hg. The patient is arousable to voice. On physical examination, there is evidence of right-sided weakness and sensory loss. CD4 count is undetectable. MRI of the brain with contrast reveals a solitary, periventricular ring-enhancing lesion. Which of the following is the most likely etiology of this patient’s condition?
The Epstein-Barr virus, or EBV, also known as human herpesvirus-4, or HHV-4, is an enveloped virus of the Herpesviridae family, which contains linear, double-stranded DNA.
EBV infection begins when saliva or respiratory secretions that contain the virus from one person make their way into someone else’s mouth.
Often, this happens by sharing food or drinks, or by kissing, which is why mono is sometimes called the “kissing disease” and why it is most common in adolescents and young adults, aged 15-24, because young people are often doing the smooching.
When EBV reaches the new person’s mouth, it infects two types of cells in the oropharynx: epithelial cells, which line the surfaces of the oropharynx, and B cells, which are lymphocytes, or lymphoid cells, that create antibodies to fight off infections.
In the epithelial cells, the virus undergoes the lytic cycle, whereby its DNA gets transcribed and translated by cellular enzymes, which help to form viral proteins, which are packaged into new viruses, which can leave the host cell destroyed, or lysed, and subsequently infect neighboring epithelial cells.
The viruses that reach the lymphoid tissue of the oropharynx, the tonsils, infect their main target, B cells, by attaching to their CD21 receptor, also known as the CR2 receptor.
The infected B cells then enter the latent phase, in which the virus just sort of hangs out in the host cell instead of killing it.
The body’s immune system reacts to the infection by mounting a humoral response, whereby the B cells create antibodies to fight off the virus, and a cellular response, in which cytotoxic (or CD8+) T cells, which are lymphocytes that mature in the thymus, work to kill the infected B cells.
This limits their ability to continue to spread the virus throughout the lymphoid tissues, thus stopping the infection from spreading.
Now, in most EBV-infected individuals, the infection is controlled, and, as a result, most people do not develop symptoms.
When someone infected with EBV does develop symptoms, that’s called infectious mononucleosis or mono.
The inflammation of the throat makes sense since the epithelial cells are infected, and swollen lymph nodes makes sense since infected B cells spread throughout the lymph tissue of the body, causing it to swell up.
The lymph nodes that are most commonly swollen as a result of an EBV infection are the posterior cervical lymph nodes in the back of the neck, because those lymph nodes drain the tonsils where the B cells are initially infected.
Another very common symptom of mono is fatigue, or extreme tiredness, which can be particularly severe in mono and can last for several months.
Other possible symptoms include tonsillitis, or inflammation of the tonsils, palatal petechiae, or red spots on the palate, hepatomegaly, or an enlarged liver, and splenomegaly, or an enlarged spleen.
The tonsillitis may be exudative or non-exudative, meaning there may or may not be white-ish or gray-ish fluid oozing out of the tonsils.
The palatal petechiae is a result of damage done to the infected epithelial cells on the palate, and the hepatomegaly and splenomegaly are a result of the liver and spleen being lymph tissues through which infected B cells flow as cytotoxic T cells try to kill them, causing those organs to swell up.
The splenomegaly, though rare, is of particular importance because an enlarged spleen is more susceptible to rupture, and splenic rupture can result in excessive bleeding and even death.
Another rare symptom of mono is a rash with faint, non-itchy, pink macules or patches that show up on the trunk and arms.