False-Positive Monospot in a Returning Traveler with Dengue Fever

Area of Science:

• Infectious Diseases
• Virology
• Immunology

Background:

• The heterophile antibody (Monospot) test is commonly used for diagnosing Epstein-Barr virus (EBV)-associated infectious mononucleosis.
• While sensitive and specific, false positive Monospot tests can occur in various conditions, including other viral infections.
• Dengue virus, an RNA flavivirus, is known to cross-react with antibodies to other flaviviruses.

Purpose of the Study:

• To report a unique case of a potential false positive heterophile antibody test in a patient with dengue fever.
• To investigate the cross-reactivity between dengue virus infection and Epstein-Barr virus heterophile antibody testing.

Main Methods:

• Case presentation of a 46-year-old male traveler returning from the Philippines with fever and symptoms.
• Initial laboratory evaluation including a positive heterophile antibody test.
• Subsequent diagnostic workup for fever in a returning traveler, including dengue virus testing (IgM and IgG) and EBV-specific tests (EBV DNA PCR, IgM by viral capsid antigen).

Main Results:

• The patient presented with fever, thrombocytopenia, and a positive heterophile antibody test.
• Dengue virus infection was confirmed by positive IgM and IgG.
• EBV-specific tests, including EBV DNA PCR and IgM by viral capsid antigen, were negative, ruling out acute EBV infection.

Conclusions:

• This case suggests a potential cross-reactivity between dengue virus infection and the heterophile antibody test.
• The findings indicate that dengue fever should be considered in the differential diagnosis of a positive Monospot test, especially in endemic areas or travelers.
• Further research may be needed to elucidate the mechanisms of this observed cross-reactivity between a flavivirus and a herpesvirus antibody test.