What are the symptoms of Infectious Mononucleosis (Mono)?

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Last updated: April 20, 2025View editorial policy

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From the Guidelines

Mono symptoms are typically caused by the Epstein-Barr virus (EBV) and can be diagnosed through a combination of physical examination, laboratory tests, and medical history, with a focus on relieving symptoms and preventing complications. The symptoms of mono usually appear 4-6 weeks after infection with EBV and can include extreme fatigue, sore throat, fever, swollen lymph nodes in the neck and armpits, swollen tonsils, headache, skin rash, and soft, swollen spleen 1.

Diagnosis and Treatment

To diagnose mono, a physical examination and medical history are essential, and laboratory tests such as a complete blood count (CBC) and heterophile antibody test (Monospot test) can be used to confirm the diagnosis 1. If the Monospot test is negative, additional laboratory testing, including EBV antibody testing for IgG and IgM to viral capsid antigen (VCA) and Epstein-Barr nuclear antigen (EBNA), may be considered to differentiate EBV infection from other causes of mononucleosis-like illness 1.

Management of Symptoms

Treatment for mono focuses on relieving symptoms while the body fights the infection, and may include:

  • Taking acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) for fever and pain
  • Gargling with salt water for sore throat
  • Getting plenty of rest
  • Avoiding strenuous activity and contact sports for at least 3-4 weeks to prevent splenic rupture
  • Staying hydrated and consuming soft foods if swallowing is difficult
  • Avoiding sharing drinks, food, or personal items while sick to prevent the spread of the virus

Complications and Prognosis

Most symptoms of mono improve within 2-4 weeks, though fatigue may persist for several months 1. However, complications can occur, and if symptoms are severe or include difficulty breathing, severe abdominal pain, or extreme weakness, immediate medical attention is necessary. EBV is also associated with lymphoproliferative disease in patients with congenital or acquired immunodeficiency, and increases in EBV viral load detected by nucleic acid amplification testing (NAAT) in peripheral blood may be present in patients before the development of EBV-associated lymphoproliferative disease 1.

From the Research

Mono Symptoms

The symptoms of mono, also known as infectious mononucleosis, can vary from person to person. Some common symptoms include:

  • Fever
  • Tonsillar pharyngitis
  • Lymphadenopathy
  • Fatigue, which can be profound but tends to resolve within three months 2
  • Periorbital and/or palpebral edema, typically bilateral, occurs in one-third of patients 2
  • Splenomegaly and hepatomegaly occur in approximately 50% and 10% of cases, respectively 2
  • A skin rash, which is usually widely scattered, erythematous, and maculopapular, occurs in approximately 10 to 45% of cases 2

Diagnosis and Clinical Interpretation

Diagnosing mono can be challenging, especially in atypical cases. The classic triad of symptoms includes fever, pharyngitis, and lymphadenopathy 3. Laboratory tests, such as the monospot test, can help confirm the diagnosis 2. It is essential to distinguish viral from bacterial infection to prevent unnecessary administration of antibiotics and other expensive exploratory tests 3.

Complications and Treatment

In some cases, mono can lead to complications such as spontaneous splenic rupture, which occurs in 0.1 to 0.5% of patients 2. Treatment is mainly supportive, and patients are advised to avoid contact sports or strenuous exercise for 8 weeks or while splenomegaly is still present 2. Prompt diagnosis is essential to avoid unnecessary investigations and treatments and to minimize complications 2.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Infectious Mononucleosis: An Updated Review.

Current pediatric reviews, 2024

Research

Infectious Mononucleosis: diagnosis and clinical interpretation.

British journal of biomedical science, 2021

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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