Babesiosis
Babesiosis is a tick-borne disease caused primarily by a microscopic parasite, Babesia microti. In the United States, infection most often occurs through the bite of an infected blacklegged (“deer”) tick (Ixodes scapularis).
Although uncommon, babesiosis can also be transmitted through a blood transfusion or from an infected pregnant person to their baby during pregnancy or delivery. Many infected individuals experience no symptoms. When illness does occur, effective treatment is available; however, delayed diagnosis or certain underlying medical conditions can increase the risk of severe disease.
The most effective way to reduce the risk of babesiosis is to prevent tick bites.
About Babesiosis
Information for Clinicians
- Clinical Guidance (CDC)
- National Surveillance Case Definition
- Connecticut Provider Reporting Information
- Connecticut 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 Babesiosis Surveillance
The Connecticut Department of Public Health (DPH) added babesiosis to the list of statewide reportable diseases in 1990. A national surveillance case definition was established by the Centers for Disease Control and Prevention in 2011.
Since 2011, an average of 216 cases of babesiosis (range: 52–311) have been reported to DPH each year. Babesiosis is the second most commonly reported tick-borne disease in Connecticut. Due to delays in case follow-up, current case counts may not represent all cases occurring in a given year.
Connecticut Annual Infectious Diseases Statistics
Last updated 2/11/2026