Ehrlichiosis

Ehrlichiosis (formerly called human monocytic ehrlichiosis) is most commonly caused by the bacterium Ehrlichia chaffeensis, and less commonly by Ehrlichia ewingii. It is spread to people through the bite of an infected Lone Star Tick (Amblyomma americanum). The bacterium can cause severe illness in some people. Treatment is available; however if it is delayed, or there are underlying medical conditions, symptoms can become more severe. The best way to prevent Ehrlichiosis is to prevent tick bites.

About Ehrlichiosis

Information for Clinicians

Clinical Guidance (CDC)

National Surveillance Case Definition (2024)

Provider Reporting Information

Laboratory Reporting Information

Directory of Clinical Testing Services provided by the State Public Health Laboratory

State Public Health Laboratory Contacts – for additional information

Tick-borne Diseases of the United States – a Reference Manual for Healthcare Providers (2022)

Connecticut Ehrlichiosis Surveillance

In 2008, the Centers for Disease Control and Prevention established a national surveillance case definition for Ehrlichiosis and the Connecticut Department of Public Health (DPH) added the disease to the list of state-wide reportable diseases. In the past 5 years (2019–2023) 28 cases have been reported to DPH. Ehrlichia chaffeensis is the main cause of illness in Connecticut. Other species include Ehrlichia ewingii and Ehlichia muris.

Connecticut Annual Infectious Diseases Statistics

Last updated 1/29/2025