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This article explores the diagnosis and treatment of ehrlichiosis, a tick borne illness. It is part two of a four part series “Four Tickborne Diseases: Lyme Disease, Ehrlichiosis, Anaplasmosis and Babesiosis” .

Diagnosis can be challenging, as the tick bite may not have been noticed, clinical symptoms may be non-specific, and laboratory confirmation of infection can be problematic, especially early in the course of these diseases. At times clinicians may need to treat on clinical suspicion alone.

Written for the Curious (Non-Medical) Reader


ehrlichiosis map of activity

Ehrlichiosis is caused by three bacteria, Ehrlichia chaffeensis, Ehrlichia ewingii, or Ehrlichia muriseauclairensis. The majority of reported cases are due to infection with E. chaffeensis. E. chaffeensis and E. ewingii are carried by the lone star tick, Amblyomma americanum, found primarily in the south-central and eastern United States. E. muris eauclairensis is carried by the blacklegged tick, Ixodes scapularis, but despite this tick’s wide distribution has only been reported in Wisconsin and Minnesota.[26] In 2018, there were 1,799 cases of E. chaffeensis reported to the CDC. The other Ehrlichia infections are much rarer, with only 218 cases of E. ewingiiehrlichiosis reported to CDC from 2008–2018, and about 115 cases of ehrlichiosis caused by E. muris eauclairensis reported since its discovery in 2009.[27]

Ehrlichia are small bacteria, round or ellipsoidal in shape. They preferentially invade white blood cells and form bacterial microcolonies known as morulae.[28]

Ehrlichiosis should be considered in patients in endemic areas with a non-specific febrile illness of unknown origin, particularly during spring and summer months when ticks are most active. Ehrlichiosis can occur alone or as a co-infection with other tickborne illnesses such as Lyme disease.

Read more about:

  • Early Signs and Symptoms of Ehrlichiosis

  • Late Symptoms of Ehrlichiosis

  • Laboratory Findings in Ehrlichiosis

  • Testing for Ehrlichiosis

  • Treatment of Ehrlichiosis


The conclusion to Part 1-4 of this article is available in the FibonacciLIBRARY

The CME version of this article is available for the medical community with an online CME test in the APP.

Not an APP member? Membership info.



Stuart M. Caplen, MD, FACEP, MSM

Dr. Caplen is a retired emergency medicine physician and former emergency department medical director, who also has a Master of Science in Management degree, and green belt certification in Lean/Six Sigma.


[3] Tickborne Diseases of the United States, CDC, last reviewed September 22, 2020. Retrieved from:

[15] Tickborne Diseases of the United States, CDC, 5th edition 2018. Retrieved from:

[15A] Signs and Symptoms of Untreated Lyme Disease, CDC, last reviewed: January 15, 2021. Retrieved from:

[16] Photo credits: Alison Young, Taryn Holman, Yevgeniy Balagula/, Lyme Disease Rashes and Look-alikes, CDC, last reviewed: October 9, 2020. Retrieved from:

[17] Photo Credit: Bernard Cohen/, Lyme Disease Rashes and Look-alikes, CDC, last reviewed: October 9, 2020. Retrieved from:

[18] Moniuszko-Malinowska A, Czupryna P, Dunaj J, et al. Acrodermatitis chronica atrophicans: various faces of the late form of Lyme borreliosis. Postepy Dermatol Alergol. 2018;35(5):490-494. Retrieved from:

[19] Photo credit, Glatz M et al., Clinical Spectrum of Skin Manifestations of Lyme Borreliosis in 204 Children in Austria, Advances in Dermatology and Venereology, Vol 95, Issue 5, Nov 4, 2014. Retrieved from:

[20] Warshafsky S et al., Efficacy of antibiotic prophylaxis for the prevention of Lyme disease: an updated systematic review and meta-analysis, Journal of Antimicrobial Chemotherapy, Volume 65, Issue 6, June 2010, Pages 1137–1144. Retrieved from:

[21] Nadelman R et al., Prophylaxis with Single-Dose Doxycycline for the Prevention of Lyme Disease after an Ixodes scapularis Tick Bite, N Engl J Med 2001; 345:79-84. Retrieved from:

[22] Photo Credit- Ticks Image Gallery, CDC, last reviewed: December 18, 2020. Retrieved from:

[23] Smith G et al., Management of Tick Bites and Lyme Disease During Pregnancy, J Obstet Gynaecol Can 2012;34(11):1087–1091. Retrieved from:

[24] Treatment for erythema migrans, CDC, last reviewed: November 3, 2020. Retrieved from:

[25] Post-Treatment Lyme Disease Syndrome, CDC, last reviewed: November 8, 2019. Retrieved from:

[26] Ehrlichiosis Transmission, CDC,last reviewed: January 17, 2019. Retrieved from:

[27] Ehrlichiosis Epidemiology and Statistics, CDC, last reviewed: March 26, 2020. Retrieved from:

[28] Ehrlichiosis Clinical and Laboratory Diagnosis, CDC, last reviewed: January 17, 2019. Retrieved from:

[29] Ehrlichiosis Signs and Symptoms, CDC, last reviewed: January 17, 2019. Retrieved from:

[30] Ehrlichiosis Treatment, CDC, last reviewed: January 17, 2019.Retrieved from:

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