Which viral illness can manifest with symptoms such as mononucleosis?

The Epstein-Barr virus is recognized as a primary cause of infectious mononucleosis, commonly known as mono. This condition is characterized by symptoms such as fever, sore throat, swollen lymph nodes, and fatigue. The virus is part of the herpesvirus family and is typically transmitted through saliva, often highlighted by its association with teenagers and young adults.

Infectious mononucleosis occurs due to the virus's affinity for B lymphocytes, leading to their proliferation and the subsequent immune response that results in the classic symptoms. Laboratory findings often support the diagnosis of Epstein-Barr virus infection through the presence of atypical lymphocytes and positive heterophile antibodies (the Monospot test).

While other viruses like Cytomegalovirus can also cause mononucleosis-like symptoms, Epstein-Barr virus is the most commonly associated agent with this illness, making it the primary answer in this scenario.