Which of the following are viral infections: Epstein-Barr virus (EBV) and cytomegalovirus (CMV), Rocky Mountain spotted fever (RMSF) and Q fever, malaria and toxoplasmosis, or histoplasmosis and cryptococcosis?

Viral Infections: Epstein-Barr Virus and Cytomegalovirus

Epstein-Barr virus (EBV) and cytomegalovirus (CMV) are the only viral infections among the listed options.

Classification of Infectious Agents

Viral Infections

• Epstein-Barr virus (EBV) and cytomegalovirus (CMV): Both are members of the herpesvirus family and cause viral infections 1
  • EBV is specifically identified as a viral infection in the IDSA/ASM guidelines 1
  • CMV is also explicitly classified as a viral infection 1

Non-Viral Infections

1. Bacterial Infections:

   • Rocky Mountain spotted fever and Q fever: Both are rickettsial diseases (bacterial infections)
     • Rocky Mountain spotted fever is caused by Rickettsia rickettsii 1
     • Q fever is caused by Coxiella burnetii, a bacterium formerly classified as Rickettsia 1

2. Parasitic Infections:

   • Malaria and toxoplasmosis: Both are parasitic infections
     • Malaria is caused by Plasmodium parasites 1
     • Toxoplasmosis is caused by the parasite Toxoplasma gondii 1

3. Fungal Infections:

   • Histoplasmosis and cryptococcosis: Both are fungal infections
     • Histoplasmosis is caused by the fungus Histoplasma capsulatum 1
     • Cryptococcosis is caused by the fungus Cryptococcus species 1

Characteristics of EBV and CMV as Viral Infections

Epstein-Barr Virus (EBV)

• Causes infectious mononucleosis (IM) 2
• Diagnosed through serological testing patterns:
  • Acute infection: VCA IgM (+), VCA IgG (+), EBNA IgG (-) 2
  • Past infection: VCA IgM (-), VCA IgG (+), EBNA IgG (+) 2
• Can cause liver manifestations ranging from asymptomatic hepatitis to acute liver failure 3
• Associated with lymphoproliferative disorders, especially in immunocompromised patients 2, 4

Cytomegalovirus (CMV)

• Second most common cause of mononucleosis syndrome 5
• Leading cause of congenital infection in developed countries 5
• Can cause severe disease in immunocompromised patients 6
• Treatment includes antivirals such as ganciclovir and valganciclovir 5
• Clinical presentation differs from EBV mononucleosis:
  • Typically affects older adults (median age 34 vs. 20 for EBV) 7
  • Longer duration of fever (median 14 days vs. 5 days for EBV) 7
  • Less likely to present with sore throat, cervical lymphadenopathy, and tonsil enlargement 7

Key Distinctions Between Categories

The classification of infectious agents is based on the type of microorganism:

• Viruses (like EBV and CMV): Non-cellular infectious agents that require host cells to replicate
• Bacteria (like those causing RMSF and Q fever): Single-celled microorganisms
• Parasites (like those causing malaria and toxoplasmosis): Complex organisms that live on or in a host
• Fungi (like those causing histoplasmosis and cryptococcosis): Eukaryotic organisms with cell walls

Clinical Implications

Understanding the correct classification of infectious agents is crucial for:

• Selecting appropriate diagnostic tests
• Choosing effective antimicrobial therapy (antivirals for viral infections, antibiotics for bacterial infections, etc.)
• Predicting disease course and potential complications
• Implementing appropriate infection control measures

Remember that while all these agents can cause fever in returning travelers 1, their management differs significantly based on their biological classification.