Black-legged (Deer) Tick


Babesiosis is mostly caused by a microscopic parasite, Babesia microti. The main way people get babesiosis is through the bite of an infected Black-legged (“deer”) tick (Ixodes scapularis). Although very rare, it is possible for the bacteria to be transmitted through a blood transfusion or from an infected mother to her baby during pregnancy or delivery. Many people who are infected experience no symptoms. When people do get sick from the infection treatment is available; however if it is delayed, or there are underlying medical conditions, symptoms can become more severe. The best way to prevent babesiosis is to prevent tick bites.


About Babesiosis


Information for Clinicians


Clinical Guidance (CDC)

National Surveillance Case Definition


Connecticut Provider Reporting Information

Reportable Disease Confidential Case Report, PD-23 

Connecticut Laboratory Reporting Information

Reportable Laboratory Findings form, OL-15C


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


Connecticut Babesiosis Surveillance

The Connecticut Department of Public Health (DPH) added babesiosis to the list of state-wide reportable diseases in 1990. The Centers for Disease Control and Prevention established a surveillance case definition in 2011.  Since 2011, an average of 216 cases (range 52 to 311) have been reported to the DPH annually. Babesiosis is the second most commonly reported tick-borne disease in Connecticut. Due to the delay in follow-up, current case counts do not represent all cases of babesiosis.

Cases of Babesiosis reported to the DPH from January 1 – December 31, 2019.


236 Confirmed


Connecticut Annual Infectious Diseases Statistics




This page last updated 1/14/2020.