Which of the following are examples of rickettsial infections: Rocky Mountain spotted fever and Q fever, malaria and toxoplasmosis, histoplasmosis and cryptococcosis, or Epstein-Barr virus and cytomegalovirus?

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Rickettsial Infections

Rocky Mountain spotted fever and Q fever are examples of rickettsial infections, while the other options are not rickettsial diseases. 1, 2

Classification of Rickettsial Infections

Rickettsial infections are caused by bacteria in the order Rickettsiales and are primarily transmitted by arthropod vectors, especially ticks. According to CDC guidelines, tickborne rickettsial diseases in the United States include:

  • Spotted Fever Group Rickettsioses:

    • Rocky Mountain spotted fever (RMSF) caused by Rickettsia rickettsii
    • Other spotted fever rickettsioses caused by Rickettsia parkeri and Rickettsia species 364D

  • Ehrlichioses:

    • Human monocytic ehrlichiosis caused by Ehrlichia chaffeensis
    • Other ehrlichioses caused by Ehrlichia ewingii and Ehrlichia muris-like agent

  • Anaplasmosis:

    • Human granulocytic anaplasmosis caused by Anaplasma phagocytophilum

  • Q fever:

    • Caused by Coxiella burnetii 1, 2

Non-Rickettsial Infections in the Question Options

The other disease pairs mentioned in the question are not rickettsial infections:

  • Malaria and toxoplasmosis:

    • Malaria is caused by protozoan parasites of the genus Plasmodium
    • Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii

  • Histoplasmosis and cryptococcosis:

    • Both are fungal infections
    • Histoplasmosis is caused by Histoplasma capsulatum
    • Cryptococcosis is caused by Cryptococcus neoformans or Cryptococcus gattii

  • Epstein-Barr virus and cytomegalovirus:

    • Both are viral infections belonging to the herpesvirus family 2

Key Features of Rickettsial Infections

  • Transmission: Primarily through arthropod vectors (ticks, lice, fleas, or mites)
  • Clinical presentation: Typically include fever, headache, myalgia, and often rash
  • Treatment: Doxycycline is the drug of choice for all rickettsial diseases in patients of all ages 2, 3
  • Seasonal occurrence: Majority of cases occur during spring and summer months, corresponding with tick activity 1

Epidemiology and Distribution

  • RMSF and ehrlichiosis are most commonly reported in the southeastern and south central United States
  • Anaplasmosis is reported predominantly in the northeastern United States, Minnesota, and Wisconsin
  • Q fever has a worldwide distribution 1

Pathophysiology

  • Rocky Mountain spotted fever involves infection of endothelial cells, causing vasculitis that can lead to rash and potentially life-threatening organ damage
  • Ehrlichioses and anaplasmosis are characterized by infection of leukocytes (monocytes or granulocytes)
  • Q fever is unique among rickettsial diseases as it is primarily transmitted through inhalation rather than tick bite 1, 2

Understanding the correct classification of these infections is essential for proper diagnosis and treatment, as rickettsial infections require specific antibiotic therapy (primarily doxycycline) and can be life-threatening if not promptly treated.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Guideline

Rickettsial Infections Guideline

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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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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