ContentsSynopsisCodesLook ForDiagnostic PearlsDifferential Diagnosis & PitfallsBest TestsManagement PearlsTherapyReferencesView all Images (10)
Human Anaplasmataceae infection
Other Resources UpToDate PubMed

Human Anaplasmataceae infection

Print Images (10)
Contributors: Tara Babu MD, William Bonnez MD, Mukesh Patel MD
Other Resources UpToDate PubMed


Human ehrlichiosis and anaplasmosis refer to infections due to bacteria belonging to the family Anaplasmataceae. Three species of this family are responsible for the majority of human infections: Anaplasma phagocytophilum, which causes human granulocytotropic (or granulocytic) anaplasmosis (HGA), Ehrlichia chaffeensis, which causes human monocytic ehrlichiosis (HME), and Ehrlichia ewingii. Ehrlichia canis is also a very rare cause of human disease.

Sennetsu fever is caused by Neorickettsia sennetsu (formerly Ehrlichia sennetsu); it may be transmitted by trematodes in fish and causes a mono-like illness with fever, lymphadenopathy, myalgia, and headache. Sennetsu fever may pose risk to inhabitants and travelers to Japan and Malaysia but is no longer considered an ehrlichiosis.

Tick vectors and specific mammalian hosts (eg, deer, dogs, mice, and cattle) form the natural zoonotic cycle for the bacteria of human ehrlichiosis and anaplasmosis. Infection follows bites from infected ticks. The vectors for A phagocytophilum include various tick species belonging to the genus Ixodes in the United States and Europe. Ehrlichia chaffeensis is transmitted by the lone-star tick, Amblyomma americanum, which is also responsible for transmission of E ewingii.

The incidence of human infection corresponds with the distribution of the arthropod vectors. In the United States, HGA is most commonly reported in New England and the north-central states as well as localized areas along the western coast. HME and E ewingii infection are most commonly reported in the southeastern, south-central, and mid-Atlantic states. Similar to other tick-borne illnesses, the majority of disease occurs in the warmer months of spring and summer and is more frequently noted to occur in men. HGA has been reported from several European countries.

Symptoms of HGA and HME typically occur 5-21 days after a bite from an infected tick. The most common symptoms are nonspecific and include fever (virtually ubiquitous), headache, malaise, and myalgias. The spectrum of disease ranges from asymptomatic to severe illness and, rarely, death. Immunocompromised individuals are at a higher risk for more severe illness, with an increased risk of mortality. HGA has a lower mortality than HME: < 1% versus 3%.

Other symptoms may include nausea, vomiting, diarrhea, cough, arthralgias, stiff neck, and confusion. In more severe illness, symptoms may also include severe respiratory distress, sepsis-like illness, rhabdomyolysis, hemorrhage, and opportunistic infections (including herpes simplex virus and fungal infections). Aseptic meningitis and meningoencephalitis are the most common neurologic symptoms noted in HME (occurring in up to 20%), and late manifesting cranial nerve palsies can occur. Central nervous system involvement is less common in HGA, although various peripheral nervous system disorders including facial palsy, brachial plexopathy, and demyelinating polyneuropathy have been reported.

Infection with E ewingii appears to produce similar clinical disease to HME and HGA, although perhaps milder in severity.

Transmission of A phagocytophilum has occurred through blood transfusion and perinatally.


A77.40 – Ehrlichiosis
A77.49 – Other ehrlichiosis

427481004 –  Human anaplasmosis
77361002 – Ehrlichiosis

Look For

Subscription Required

Diagnostic Pearls

Subscription Required

Differential Diagnosis & Pitfalls

Best Tests

Subscription Required

Management Pearls

Subscription Required


Subscription Required


Subscription Required

Last Updated: 04/15/2020
Copyright © 2020 VisualDx®. All rights reserved.
Human Anaplasmataceae infection
Print 10 Images
View all Images (10)
(with subscription)
Human Anaplasmataceae infection (Ehrlichiosis (Adult)) : Chills, Fever, Headache, ALT elevated, AST elevated, Leukopenia, Tick bite, Arthralgia, PLT decreased
Clinical image of Human Anaplasmataceae infection
Copyright © 2020 VisualDx®. All rights reserved.