Ehrlichiosis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ilan Dock, B.S.

Overview

Three strains of Ehrlichia (E. ewingii, E. chaffeensis, and E. Muris) are responsible for human infection. These resulting infections present themselves with very similar, if not the same, clinical manifestations. Endemic regions are different among the different diseases which may be used to diagnose the organism of infection.

Classification

• Ehrlichiosis is a broadly used medical term for multiple bacterial infections.
• Four species have been identified in Human infections:

1. Ehrlichia Ewingii
2. Ehrlichia Chaffeensis
3. Ehrlichia Muris
4. Anaplasma phagocytophilum

• Infections with the above organism have similar or the same clinical presentation.
• Endemic Regions are different according to specific species.

• There are four types of Ehrlichia infections, human monocytotropic ehrlichiosis (HME), human ehrlichiosis ewingii (HEE), human muris-like (HML) and human granulocytotropic anaplasmosis (HGA), previously referred to as human granulocytotropic ehrlichiosis (HGE).
• HME is primarily transmitted by the Lone Star Tick (Amblyomma Americanum).
• HGA is caused by phagocytophilum.
• HEE and HML are caused by Ehrlichia ewingii and Ehrlichia muris respectively.
• Clinical presentation is similar between HME, HEE, HML, and HGA, with symptoms such as fever, headache, and leukopenia.
• HME however has proven to be more fatal than other Ehrlichia infections, including CNS and neurological disorders inflicting nearly 20% of all infected patients.

Organism	Disease	Vector	Endemic Regions	Common Symptoms
Ehrlichia ewingii	Human ehrlichiosis ewingii (HEE)	Lone Star Tick (Amblyomma americanum)	Southeastern and South Central United States	Similar symptoms to those of HME and HGA. Although not much has been documented due to the minor amount of reported cases.
Ehrlichia chaffeensis	Human Monocytotropic Ehrlichiosis	Lone Star Tick (Amblyomma americanum)	Mississippi, Tennessee, Arkansas, and Maryland. South central and Southeastern United States.	More Severe than HGA and HEE. Clinical manifestations include gastrointestinal symptoms, headaches, myalgias, and arthralgias. It's been documented that 20% of infected patients have neurological manifestations, CNS complications, potential seizures and coma. Potential rash, however the rash may indicate a co-infection between Rocky Mountain Spotted Fever and Ehrlichiosis.
Ehrlichia muris	Ehrlichiosis muris-like (EML)	Not yet established	Minnesota and Wisconsin	Common symptoms include fever, malaise, thrombocytopenia, and lymphopenia.
Anaplasma phagocytophilum	Human Granulocytotropic Anaplasmosis	Black-legged Tick (Ixodes scapularis)	Occurs worldwide (including portions of Europe and Asia.)	Fever, headache, and myalgias. Rash is uncommon, and CNS disorders as well as neurological issues have been reported in less than 1%.