Right out of the CDC or is it Sci-Fi - the Epstein-Barr virus
https://www.cdc.gov/epstein-barr/about-ebv.html
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Epstein-Barr virus (EBV), also known as human herpesvirus 4, is a member of the herpes virus family. It is one of the most common human viruses. EBV is found all over the world. Most people get infected with EBV at some point in their lives. EBV spreads most commonly through bodily fluids, primarily saliva. EBV can cause infectious mononucleosis, also called mono, and other illnesses.
Symptoms
Symptoms of EBV infection can include
Sick child in bed
fatigue
fever
inflamed throat
swollen lymph nodes in the neck
enlarged spleen
swollen liver
rash
Many people become infected with EBV in childhood. EBV infections in children usually do not cause symptoms, or the symptoms are not distinguishable from other mild, brief childhood illnesses. People who get symptoms from EBV infection, usually teenagers or adults, get better in two to four weeks. However, some people may feel fatigued for several weeks or even months.
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We sure are fatigued